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Abstract

The involvement of the left temporal lobe in semantics and object naming has been repeatedly demonstrated in the context of language comprehension; however, its role in the mechanisms and time course for the retrieval of an integrated object memory from its constituent features have not been well delineated. In this study, 19 young adults were presented with two features of an object (e.g., "desert" and "humps") and asked to determine whether these two features were congruent to form a retrieval of a specific object ("camel") or incongruent and formed no retrieval while event-related potentials (ERP) were recorded. Beginning around 750 ms the ERP retrieval and nonretrieval waveforms over the left anterior fronto-temporal region show significance differences, indicating distinct processes for retrievals and nonretrievals. In addition to providing further data implicating the left frontal-anterior temporal region in object memory/retrieval, the results provide insight into the time course of semantic processing related to object memory retrieval in this region. The likely semantic process at 750 ms in this task would be coactivation of feature representations common to the same object. The consistency of this finding suggests that the process is stable across individuals. The potential clinical applications are discussed.

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... An ERP study of young adults using SORT showed a left frontotemporal component starting at around 750 ms post-stimulus that was more negative in retrieval than in non-retrieval stimulus pairs (Brier et al., 2008), suggestive of object memory activation. This finding was later replicated in a different group of young adults as well as in a group of normal aging subjects (Chiang et al., 2014), and even in a group of cognitively impaired subjects (Chiang et al., 2015). ...
... First, we used conventional window measured ERP analysis to examine if the current study replicated previous findings (Brier et al., 2008;Chiang et al., 2014Chiang et al., , 2015. We extracted mean amplitude during the time window between 750 and 1000 ms post-2nd stimulus over the left fronto-temporal area (F7) which has been used in prior reports. ...
... p = .042, Cohen's D = 0.56, with retrieval (−2.36 uV) more negative than non-retrieval trials (−1.12 uV), consistent with previous reports (Brier et al., 2008;Chiang et al., 2014Chiang et al., , 2015. Subsequently, by including all tasks and conditions, we found a strong main effect of condition, F(1,45) = 21.9, p < .001, ...
Article
To test the hypothesis that semantic processes are represented in multiple subsystems, we recorded electroencephalogram (EEG) as we elicited object memories using the modified Semantic Object Retrieval Test, during which an object feature, presented as a visual word [VW], an auditory word [AW], or a picture [Pic], was followed by a second feature always presented as a visual word. We performed both hypothesis-driven and data-driven analyses using event-related potentials (ERPs) time locked to the second stimulus. We replicated a previously reported left fronto-temporal ERP effect (750–1000 ms post-stimulus) in the VW task, and also found that this ERP component was only present during object memory retrieval in verbal (VW, AW) as opposed to non-verbal (Pic) stimulus types. We also found a right temporal ERP effect (850–1000 ms post-stimulus) that was present in auditory (AW) but not in visual (VW, Pic) stimulus types. In addition, we found an earlier left temporo-parietal ERP effect between 350 and 700 ms post-stimulus and a later midline parietal ERP effect between 700 and 1100 ms post-stimulus, present in all stimulus types, suggesting common neural mechanisms for object retrieval processes and object activation, respectively. These findings support multiple semantic subsystems that respond to varying stimulus modalities, and argue against an ultimate unitary amodal semantic analysis.
... In that study, subjects were presented with two words that represent features of objects and were asked to indicate whether the words together resulted in retrieval of a specific object from memory. Neural correlates of normal subjects performing this task have been studied using behavioral [9], fMRI [10][11][12], event related potential (ERP) [13], and electroencephalographic time-frequency analysis [14,15] techniques. The task has also been used to probe dysfunction in patients with mild cognitive impairment and/or Alzheimer's Disease [9,16,17], schizophrenia [18], stroke [19,20], and concussion and aging [21]. ...
... In a study of normal controls performing the task during fMRI, significant BOLD signal changes were detected for the correct retrievals in bilateral medial Brodmann Area 6 (pre-SMA region), dorsomedial and pulvinar thalamic nuclei, caudate nuclei, and bilateral temporo-occipital regions [10,11,21]. There is also a an ERP difference between retrievals and nonretrievals at approximately 750 ms with a maximum at the left fronto-temporal region that has been proposed to signify co-activation of common feature representations of the object being retrieved [13]. ...
... The semantic process at 750 ms that has been associated with this task has been attributed to the coactivation of feature representations common to the same object [13]. The timing of the separation between retrievals and nonretrievals was prior to memory retrieval but consistent temporally and spatially with correlating similar features. ...
Article
Gulf War veterans meeting criteria for Haley Syndrome 2 of Gulf War illness endorse a particular constellation of symptoms that include difficulty with processing information, word-finding, and confusion. To explore the neural basis of their word-finding difficulty, we assessed event-related potentials (ERPs) associated with semantic memory retrieval in 22 veterans classified as Syndrome 2 and 28 veterans who served as controls. We recorded EEGs while subjects judged whether pairs of words that represented object features combined to elicit a retrieval of an object memory or no retrieval. Syndrome 2 subjects' responses were significantly slower, and those participants were less accurate than controls on the retrieval trials, but they performed similarly on the nonretrieval trials. Analysis of the ERPs revealed a difference between retrievals and nonretrievals that has previously been detected around 750 ms at the left temporal region was present in both the Syndrome 2 patients and controls. However, the Syndrome 2 patients also showed an ERP difference between retrievals and nonretrievals at the midline parietal region that had a scalp voltage polarity opposite from that recorded at the left temporal area. We hypothesize that the similarities between task performance and ERP patterns in Syndrome 2 veterans and in patients with amnestic mild cognitive impairment reflect disordered thalamic cholinergic neural activity, possibly in the dorsomedial nucleus.
... Our group developed an EEG version of the SORT (EEG SORT) and has studied neural underpinning related to this task in young and older adults. The first study involving young adults found a left frontotemporal component (beginning at 750 ms and lasting over 1500 ms post-stimulus) differentiating retrieval from non-retrieval trials [32]. When we examined the effects of normal aging using this same paradigm employing a data-driven approach, we replicated the findings of Brier et al. study. ...
... Smaller fractionated windows (15 to 30 ms) only added to the multiple-testing burden without measurably improving the signal-to-noise ratio or the temporal resolution of mean amplitude data. We focused on the later time windows based on previous findings showing that SORT ERP effects arise later than 400 ms post-stimulus [30,32]. However, we tested the time window between 0 and 400 ms using the same analysis to examine any potential effects. ...
... Additionally, this thresholding approach reduced the noise fed to the PCA to isolate only the most salient effects [47]. We were also guided to some extent by a priori hypotheses of both timing and spatial location based on knowledge of previous findings using EEG SORT [30,32]. ...
Article
Deficits in semantic memory in individuals with amnestic mild cognitive impairment (aMCI) have been previously reported, but the underlying neurobiological mechanisms remain to be clarified. We examined event-related potentials (ERPs) associated with semantic memory retrieval in 16 individuals with aMCI as compared to 17 normal controls using the Semantic Object Retrieval Task (EEG SORT). In this task, subjects judged whether pairs of words (object features) elicited retrieval of an object (retrieval trials) or not (non-retrieval trials). Behavioral findings revealed that aMCI subjects had lower accuracy scores and marginally longer reaction time compared to controls. We used a multivariate analytical technique (STAT-PCA) to investigate similarities and differences in ERPs between aMCI and control groups. STAT-PCA revealed a left fronto-temporal component starting at around 750 ms post-stimulus in both groups. However, unlike controls, aMCI subjects showed an increase in the frontal-parietal scalp potential that distinguished retrieval from non-retrieval trials between 950 and 1050 ms post-stimulus, which negatively correlated with the performance on the logical memory subtest of the Wechsler Memory Scale- III. Thus, individuals with aMCI were not only impaired in their behavioral performance on SORT relative to controls, but also displayed alteration in the corresponding ERPs. The altered neural activity in aMCI compared to controls suggests a more sustained and effortful search during object memory retrieval, which may be a potential marker indicating disease processes at the pre-dementia stage.
... Both age groups had comparable accuracy although response times were longer in older adults. In both groups a left fronto-temporal negative potential occurred at around 750 msec during object retrieval, consistent with previous findings (Brier et al., 2008). Only in older adults a later positive frontal potential was found peaking between 800 and 1000 msec during no retrieval. ...
... An ERP study of young adults using the SORT showed a left fronto-temporal component starting at around 750 msec post-stimulus that was more negative in retrieval than nonretrieval stimulus pairs (Brier, Maguire, Tillman, Hart, & Kraut, 2008). A power analysis of the EEG changes during the SORT showed earlier alpha desynchronization (8~12 HZ)/delta synchronization (~1 Hz) as well as later frontal beta synchronization (20-35 Hz, after one second post-stimulus), which were posited to represent semantic search and object retrieval, respectively (Ferree et al., 2009;. ...
... Therefore, in view of the word stimuli used in the SORT, we hypothesized that older adults would present differences between retrieval and non-retrieval stimulus pairs around 750 msec similar to young adults in Brier et al.'s study (2008). In order to test this hypothesis, we undertook conventional windowed analyses between 750 and 1000 msec post-stimulus as in Brier et al. (2008) to replicate the results in younger adults and to examine similarities between younger and older adults in the current study. To further examine qualitative differences in ERPs between younger and older adults that might not be easily detected by visual inspection and thus windowed ERP measures, we performed data-driven exploratory analyses that prove to be a useful tool for high-density ERPs (Dien & Frishkoff, 2005;Dien, Michelson, & Franklin, 2010;Spence, Brier, Hart, & Ferree, 2013). ...
Article
Abstract To investigate neural mechanisms that support semantic functions in aging, we recorded scalp EEG during an object retrieval task in 22 younger and 22 older adults. The task required determining if a particular object could be retrieved when two visual words representing object features were presented. Both age groups had comparable accuracy although response times were longer in older adults. In both groups a left fronto-temporal negative potential occurred at around 750 msec during object retrieval, consistent with previous findings (Brier, Maguire, Tillman, Hart, & Kraut, 2008).Only in older adults a later positive frontal potential was found peakingbetween800 and 1000 msec during no retrieval.These findings suggest younger and older adults employ comparable neural mechanisms when features clearly facilitate retrieval of an object memory, but when features yield no retrieval, older adults use additional neural resources to engage in a more effortful and exhaustive search prior to making a decision.
... ERP derive from averaging of EEG epochs to capture consistent changes in phase-locked neural activity as reflected in the timing and shape of ERP waveforms (Luck, 2005). To date, several neurophysiological studies using either technique have been performed to examine semantic object memory retrieval during SORT (Ferree et al., 2009;Brier et al., 2008;Chiang et al., 2014Chiang et al., , 2015. ...
... Behaviorally, nonretrieval trials had longer RT and better accuracy compared to retrieval trials. These effects have been consistently shown in all previous SORT studies using only visual words as stimuli (Brier et al., 2008;Chiang et al., 2014Chiang et al., , 2015. As proposed before, this difference between conditions may indicate a longer and more exhaustive search in non-retrieval compared to retrieval trials that is required before making a decision (Chiang et al., 2014); this search seems to last even longer in the verbal domain (VW and AW) compared to the nonverbal domain (Pic) when non-retrieval RT was considered. ...
Article
(free download: http://authors.elsevier.com/a/1THEecAwkKMHN) Abstract How the brain combines the neural representations of features that comprise an object in order to activate a coherent object memory is poorly understood, especially when the features are presented in different modalities (visual vs. auditory) and domains (verbal vs. nonverbal). We examined this question using three versions of a modified Semantic Object Retrieval Test, where object memory was probed by a feature presented as a written word, a spoken word, or a picture, followed by a second feature always presented as a visual word. Participants indicated whether each feature pair elicited retrieval of the memory of a particular object. Sixteen subjects completed one of the three versions (N = 48 in total) while their EEG were recorded simultaneously. We analyzed EEG data in four separate frequency bands (delta: 1-4 Hz, theta: 4-7 Hz; alpha: 8-12 Hz; beta: 13-19 Hz) using a multivariate data-driven approach. We found that alpha power time-locked to response was modulated by both cross-modality (visual vs. auditory) and cross-domain (verbal vs. nonverbal) probing of semantic object memory. In addition, retrieval trials showed greater changes in all frequency bands compared to non-retrieval trials across all stimulus types in both response-locked and stimulus-locked analyses, suggesting dissociable neural subcomponents involved in binding object features to retrieve a memory. We conclude that these findings support both modality/domain-dependent and modality/domain-independent mechanisms during semantic object memory retrieval. (free download: http://authors.elsevier.com/a/1THEecAwkKMHN)
... Subjects were instructed that the target needed to be a specific object, not merely an association between the two words. Fifty trials comprised stimulus pairs that have been shown in previous work (Assaf et al., 2006;Brier et al., 2008) to elicit retrieval of a specific object, and 50 were non-retrieval trials. The same feature words used in the object retrieval pairs were used in the non-retrieval pairs, but were re-paired with a semantically unrelated word. ...
... First, this frequency band was found in this same task using intra-cranial electrodes (Slotnick et al., 2002). Second, electrode F5 was found previously by applying PCA-ANOVA to ERP analysis of the same data set (Brier et al., 2008). Third, the time duration (0.75-1.5 s) is the same as that of the ERP. ...
Article
A new method is developed for analyzing the time-varying spectral content of EEG data collected in cognitive tasks. The goal is to extract and summarize the most salient features of numerical results, which span space, time, frequency, task conditions, and multiple subjects. Direct generalization of an established approach for analyzing event-related potentials, which uses sequential PCA followed by ANOVA to test for differences between conditions across subjects, gave unacceptable results. The new method, termed STAT-PCA, advocates statistical testing for differences between conditions within single subjects, followed by sequential PCA across subjects. In contrast to PCA-ANOVA, it is demonstrated that STAT-PCA gives results which: 1) isolate task-related spectral changes, 2) are insensitive to the precise definition of baseline power, 3) are stable under deletion of a random subject, and 4) are interpretable in terms of the group-averaged power. Furthermore, STAT-PCA permits the detection of activity that is not only different between conditions, but also common to both conditions, providing a complete yet parsimonious view of the data. It is concluded that STAT-PCA is well suited for analyzing the time-varying spectral content of EEG during cognitive tasks.
... A difference of ERP activity between these retrieval and nonretrieval conditions was found in fronto-central electrodes at approximately 750 ms after the presentation of the word pair. This difference was considered to be caused by the retrieval of the word associated to the first pair (Brier et al., 2008;Tillman et al., 2017). ...
Article
Full-text available
Associative memory refers to a type of memory in which a perceived stimulus evokes specific information associated to it. Event related potential (ERP) studies of memory retrieval have focused mainly on episodic recognition memory and recently, on semantic memory retrieval as well. Even though previous investigations have proven very useful to catch a glimpse on the ERP activity underlying memory processes, they traditionally analyze ERP activity present between a stimulus presentation and a motor response, and not between one stimulus and the memory representation of another stimulus associated to it. Therefore, specific ERP activity related to associative memory retrieval has not been fully characterized. The present work represents an exploratory attempt to study the ERP activity supporting associative memory retrieval processes. To that extent, we compared two tasks which differed in the memory retrieval component, and focused our analysis on the differences in ERP activity occurring between a cue and a target presentations in both tasks. We found main differences in three time windows possibly implicated in associative memory retrieval processes. The first one takes place between 230 and 350 ms and involves fronto-central electrodes, the second one takes place at 420–560 ms in centro-posterior electrodes and the third one occurs between 830 and 940 ms mainly in posterior electrodes. Based on previous literature on ERP and memory retrieval, some hypotheses are proposed regarding the implications of those activities in associative memory retrieval. Together, the present work, although exploratory, represents an original approach to the study of associative memory through ERP.
... In healthy adults, this left frontotemporal difference has been found between 750-1000 msec. 15,16,24 We found this same distinction in our HC subjects. ...
Article
Full-text available
Individuals who have suffered a traumatic brain injury (TBI) often have word retrieval deficits; however, the underlying neural mechanisms of such deficits are yet to be clarified. Previous studies in normal subjects have shown that during a word retrieval task, there is a 750 ms event-related potential (ERP) divergence detected at the left fronto-temporal region when subjects evaluate word pairs that facilitate retrieval compared to responses elicited by word pairs that do not facilitate retrieval. In this study, we investigated the neurophysiological correlates of word retrieval networks in 19 retired professional athletes with TBI and 19 healthy controls (HC). We recorded electroencephalography (EEG) in the participants during a semantic object retrieval task (SORT). In this task, participants indicated whether presented word pairs did (retrieval) or did not (non-retrieval) facilitate the retrieval of an object name.There were no significant differences in accuracy or reaction time between the two groups. The EEG showed a significant group by condition interaction over the left-fronto-temporal region. The HC group mean amplitudes were significantly different between conditions, but the TBI group data did not show this difference, suggesting neurophysiological effects of injury. These findings provide evidence that ERP amplitudes may be used as a marker of disrupted semantic retrieval circuits in individuals with TBI even when those people perform normally.
... This may be due to aspects of the functional neuroanatomy of word-finding; word-finding and semantic processing is a complex ability often mediated by several neuroanatomical correlates including lateral temporal, temporoparietal, and anterior temporal regions (Chiang et al., 2014;Grossman et al., 2004). The anterior temporal lobes may serve as storehouses of general semantic knowledge (Brier, Maguire, Tillman, Hart, & Kraut, 2008), or knowledge of more specific concepts such as social conceptual processing (Simmons & Martin, 2009). Although some studies have linked picture-naming performance to anterior temporal lobe volume (Balthazar et al., 2010), other studies (Hamberger, Goodman, Perrine, & Tamny, 2001;Malow et al., 1996) suggest that picture naming is more closely associated with temporo-parietal brain regions, while anterior temporal regions may be more related to word-finding in response to verbal definitional prompts. ...
Article
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Naming or word-finding tasks are a mainstay of the typical neuropsychological evaluation, particularly with older adults. However, many older adults have significant visual impairment and there are currently no such word-finding tasks developed for use with older visually impaired populations. This study presents a verbal, non-visual measure of word-finding for use in the evaluation of older adults with possible dysnomia. Stimuli were chosen based on their frequency of usage in everyday spoken language. A 60-item scale was created and given to 131 older Veterans. Rasch analyses were conducted and differential item functioning assessed to eliminate poorly-performing items. The final 55-item scale had a coefficient alpha of 0.84 and correlated with the Neuropsychological Assessment Battery Naming test, r=0.84, p<.01, Delis-Kaplan Executive Function System (D-KEFS) Category Fluency, r=0.45, p<.01, and the D-KEFS Letter Fluency, r=0.40, p<.01. ROC analyses found the measure to have sensitivity of 79% and specificity of 85% for detecting dysnomia. Patients with dysnomia performed worse on the measure than patients with intact word-finding, t(84)=8.2, p<.001. Patients with no cognitive impairment performed significantly better than patients with mild cognitive impairment, who performed significantly better than patients with dementia. This new measure shows promise in the neuropsychological evaluation of word-finding ability in older adults with or without visual impairment. Future directions include the development of a shorter version and the generation of additional normative data. (JINS, 2015, 21, 1-10).
... A significant difference in the ERP between the retrieval and nonretrieval waveforms (with nonretrievals more negative than retrievals) was detected over the left anterior frontotemporal regions at about 750 ms, indicating a divergence in processing between object retrievals and nonretrievals. We propose that this ERP divergence occurs when the activated feature representations of the stimuli are correlated with each other in the trials during which an object memory is retrieved (Brier, Maguire, Tillman, Hart, & Kraut, 2008). It should be kept in mind that this rather long 750 ms interval subsumes reading the two words that represent the feature stimuli and determining what each of them means, both of which have to take place before further processing can occur. ...
Article
We propose that pre-supplementary motor area (pre-SMA)-thalamic interactions govern processes fundamental to semantic retrieval of an integrated object memory. At the onset of semantic retrieval, pre-SMA initiates electrical interactions between multiple cortical regions associated with semantic memory subsystems encodings as indexed by an increase in theta-band EEG power. This starts between 100-150ms after stimulus presentation and is sustained throughout the task. We posit that this activity represents initiation of the object memory search, which continues in searching for an object memory. When the correct memory is retrieved, there is a high beta-band EEG power increase, which reflects communication between pre-SMA and thalamus, designates the end of the search process and resultant in object retrieval from multiple semantic memory subsystems. This high beta signal is also detected in cortical regions. This circuit is modulated by the caudate nuclei to facilitate correct and suppress incorrect target memories.
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Wernicke (1900, as cited in G. H. Eggert, 1977) suggested that semantic knowledge arises from the interaction of perceptual representations of objects and words. The authors present a parallel distributed processing implementation of this theory, in which semantic representations emerge from mechanisms that acquire the mappings between visual representations of objects and their verbal descriptions. To test the theory, they trained the model to associate names, verbal descriptions, and visual representations of objects. When its inputs and outputs are constructed to capture aspects of structure apparent in attribute-norming experiments, the model provides an intuitive account of semantic task performance. The authors then used the model to understand the structure of impaired performance in patients with selective and progressive impairments of conceptual knowledge. Data from 4 well-known semantic tasks revealed consistent patterns that find a ready explanation in the model. The relationship between the model and related theories of semantic representation is discussed.
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Extracellular microelectrode recordings were obtained from lateral temporal cortex that was subsequently resected in patients undergoing craniotomies under local anaesthesia for treatment of medically intractable epilepsy. During these recordings patients performed visually presented measures of overt and silent naming and word reading, short-term verbal memory and a control task requiring matching of angles. These measures were designed so that the same visual stimuli elicited language, short-term memory or spatial responses. Statistically significant changes within and between these various measures were identified. Technically satisfactory recordings were obtained from 17 populations reflecting activity predominantly from 1 neuron, in 13 patients. Two populations demonstrated no significant changes in any measured functions. Only 1 population showed changes suggesting a relation to visual perception. Four populations in or adjacent to the superior temporal gyrus altered activity with overt speech. Four other populations in the anterior temporal lobe altered activity during silent, but not overt speech. Some relation to language or memory was established for 13 of the 17 populations: 1 altered activity during reading alone, 6 during memory alone, and 6 to both. Most of the recording sites showing these language and memory changes were not essential for those functions based on surface electrical stimulation mapping. Thus the area of temporal lobe that participates in language and memory, as indicated by changes in neuronal activity, is substantially larger than the areas essential for those functions as determined by stimulation mapping. Within that participatory area, changes related to language were most often an increase in activity sustained throughout the task, a pattern suggestive of mechanisms of selective attention. Changes related to memory most often included a sustained increase in activity at the time of entry of information into memory, and again at retrieval, with decreased activity during the time the memory was stored. A few neuronal populations demonstrated relative inhibition of activity during the memory task, compared with control measures.
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The neuroelectric activity of the human brain that accompanies linguistic processing can be studied through recordings of event-related potentials (e.r.p. components) from the scalp. The e.r.ps triggered by verbal stimuli have been related to several different aspects of language processing. For example, the N400 component, peaking around 400 ms post-stimulus, appears to be a sensitive indicator of the semantic relationship between a word and the context in which it occurs. Words that complete sentences in a nonsensical fashion elicit much larger N400 waves than do semantically appropriate words or non-semantic irregularities in a text. In the present study, e.r.ps were recorded in response to words that completed meaningful sentences. The amplitude of the N400 component of the e.r.p. was found to be an inverse function of the subject's expectancy for the terminal word as measured by its 'Cloze probability'. In addition, unexpected words that were semantically related to highly expected words elicited lower N400 amplitudes. These findings suggest N400 may reflect processes of semantic priming or activation.
Article
To evaluate the determinants of postoperative change in visual confrontation naming ability and the differential sensitivity of two common tests of confrontation naming. In a group of 99 patients undergoing lobectomy of the left, language-dominant anterior temporal lobe, we examined naming ability using two measures: the 60 item Boston Naming Test (BNT), and the Visual Naming (VN) subtest of the Multilingual Aphasia Examination (MAE). ATL entailed resection of lateral temporal lobe followed by microsurgical complete removal of hippocampus. Language mapping was not performed. The status of the resected hippocampus was graded on a scale 0-4 of hippocampal sclerosis (HS). A dichotomous grouping HS- (grades 0 and 1, n = 34) and HS+ (grades 3 and 4, n = 61) was effected. Age at surgery, age of epilepsy onset, sex, extent of lateral temporal resection, Full-Scale IQ (FSIQ), and preoperative naming scores were also examined as potential predictors of pre- versus postoperative naming change. Preoperative BNT and VN scores were significantly worse for HS+ than for HS- (BNT, p < 0.05; VN, p = 0.001). Postoperatively, BNT and VN scores significantly declined for HS- as compared with HS+ patients (p < 0.001). For individual risk, the 90th centile of reliable change index (RCI) was used. By this criterion, of the total sample, 39% evidenced decline on the BNT and 17% evidenced decline on the VN. Logistic regression analysis with backward elimination showed HS to be the only predictor of decline in BNT and HS and sex to be the only predictors of VN decline. Males were more at risk than females. Age, age at onset, extent of lateral resection, preoperative scores, and FSIQ were not predictors. Using age at onset as a proxy for HS+/HS- we calculated probabilities for naming decline for given onset age. Both preoperative and postoperative change in naming ability are associated with the pathological status of the hippocampus. The potential interpretations and implications of these findings are discussed.
Article
Semantic dementia, characterized by loss of word meaning and impaired face and object recognition, is one of the clinical manifestations of frontotemporal lobar degeneration and is associated with atrophy of the inferior and middle temporal gyri. Patients may present predominantly with problems in naming and understanding words, or in face and object recognition, the verbal or nonverbal predominance reflecting the accent of atrophy on the left or right temporal lobe. Behavioural changes may occur, although these have a more obsessional quality than is typically seen in frontotemporal dementia (FTD). However, overlap in clinical symptomatology of semantic dementia and FTD may occur with disease progression reinforcing the link between these clinical syndromes. Semantic dysfunction is poorly recognized and may be mistaken for the amnesia of Alzheimer's disease, yet may be important in explaining some of the behavioural characteristics seen in focal cerebral degeneration.
Article
Words representing concrete concepts are processed more quickly and efficiently than words representing abstract concepts. Concreteness effects have also been observed in studies using event-related brain potentials (ERPs). The aim of this study was to examine concrete and abstract words using both reaction time (RT) and ERP measurements to determine (1) at what point in the stream of cognitive processing concreteness effects emerge and (2) how different types of cognitive operations influence these concreteness effects. Three groups of subjects performed a sentence verification task in which the final word of each sentence was concrete or abstract. For each group the truthfulness judgment required either (1) image generation, (2) semantic decision, or (3) evaluation of surface characteristics. Concrete and abstract words produced similar RTs and ERPs in the surface task, suggesting that postlexical semantic processing is necessary to elicit concreteness effects. In both the semantic and imagery tasks, RTs were shorter for concrete than for abstract words. This difference was greatest in the imagery task. Also, in both of these tasks concrete words elicited more negative ERPs than abstract words between 300 and 550 msec (N400). This effect was widespread across the scalp and may reflect activation in a linguistic semantic system common to both concrete and abstract words. ERPs were also more negative for concrete than abstract words between 550 and 800 msec. This effect was more frontally distributed and was most evident in the imagery task. We propose that this later anterior effect represents a distinct ERP component (N700) that is sensitive to the use of mental imagery. The N700 may reflect the a access of specific characteristics of the imaged item or activation in a working memory system specific to mental imagery. These results also support the extended dual-coding hypothesis that superior associative connections and the use of mental imagery both contribute to processing advantages for concrete words over abstract words.
Article
How is conceptual knowledge organized and represented? Are domains (such as living things) and categories (such as tools, fruit) represented explicitly or can domain and category structure emerge out of a distributed system? Taken at face value, evidence from brain-damaged patients and neuroimaging studies suggests that conceptual knowledge is explicitly structured in independent content-based stores. However, recent analyses of the fine-grained details of semantic impairments, combined with research using connectionist modelling, suggest a different picture - one in which concepts are represented as patterns of activation over multiple semantic properties within a unitary distributed system. Within this context, category-specific deficits emerge as a result of differences in the structure and content of concepts rather than from explicit divisions of conceptual knowledge in separate stores.
Article
Recent research indicates that novel stimuli elicit at least two distinct components, the Novelty P3 and the P300. The P300 is thought to be elicited when a context updating mechanism is activated by a wide class of deviant events. The functional significance of the Novelty P3 is uncertain. Identification of the generator sources of the two components could provide additional information about their functional significance. Previous localization efforts have yielded conflicting results. The present report demonstrates that the use of principal components analysis (PCA) results in better convergence with knowledge about functional neuroanatomy than did previous localization efforts. The results are also more convincing than that obtained by two alternative methods, MUSIC-RAP and the Minimum Norm. Source modeling on 129-channel data with BESA and BrainVoyager suggests the P300 has sources in the temporal-parietal junction whereas the Novelty P3 has sources in the anterior cingulate.
Article
Using both the lesion method and functional imaging (positron emission tomography) in large cohorts of subjects investigated with the same experimental tasks, we tested the following hypotheses: (A) that the retrieval of words which denote concrete entities belonging to distinct conceptual categories depends upon partially segregated regions in higher-order cortices of the left temporal lobe; and (B) that the retrieval of conceptual knowledge pertaining to the same concrete entities also depends on partially segregated regions; however, those regions will be different from those postulated in hypothesis A, and located predominantly in the right hemisphere (the second hypothesis tested only with the lesion method). The analyses provide support for hypothesis A in that several regions outside the classical Broca and Wernicke language areas are involved in name retrieval of concrete entities, and that there is a partial segregation in the temporal lobe with respect to the conceptual category to which the entities belong, and partial support for hypothesis B in that retrieval of conceptual knowledge is partially segregated from name retrieval in the lesion study. Those regions identified here are seen as parts of flexible, multi-component systems serving concept and word retrieval for concrete entities belonging to different conceptual categories. By comparing different approaches the article also addresses a number of method issues that have surfaced in recent studies in this field.
Article
Despite decades of research, it remains controversial whether semantic knowledge is anatomically segregated in the human brain. To address this question, we recorded event-related potentials (ERPs) while participants viewed pictures of animals and tools. Within the 200-600-ms epoch after stimulus presentation, animals (relative to tools) elicited an increased anterior negativity that, based on previous ERP studies, we interpret as associated with semantic processing of visual object attributes. In contrast, tools (relative to animals) evoked an enhanced posterior left-lateralized negativity that, according to prior research, might reflect accessing knowledge of characteristic motion and/or more general functional properties of objects. These results support the hypothesis of the neuroanatomical knowledge organization at the level of object features: the observed neurophysiological activity was modulated by the features that were most salient for object recognition. The high temporal resolution of ERPs allowed us to demonstrate that differences in processing animals and tools occurred specifically within the time-window encompassing semantic analysis.
Article
The neural basis of formal thought disorder (FTD) is unknown. An influential theory is that FTD results from impaired semantic memory processing. We explored the neural correlates of semantic memory retrieval in schizophrenia using an imaging task assessing semantic object recall. Sixteen healthy control subjects and sixteen schizophrenia patients whose FTD symptoms were measured with the Thought Disorder Index completed a verbal object-recall task during functional magnetic resonance imaging. Participants viewed two words describing object features that either evoked (object recall) or did not evoke a semantic concept. Schizophrenia patients tended to overrecall objects for feature pairs that did not describe the same object. Functionally, rostral anterior cingulate cortex (ACC) activation in patients positively correlated with FTD severity during both correct recalled and overrecalled trials. Compared with control subjects, during object recalling, patients overactivated bilateral ACC, temporooccipital junctions, temporal poles and parahippocampi, right inferior frontal gyrus, and dorsolateral prefrontal cortex, but underactivated inferior parietal lobules. Our results support impaired semantic memory retrieval as underlying FTD pathophysiology. Schizophrenia patients showed abnormal activations of brain areas involved in semantic memory, verbal working memory, and initiation and suppression of conflicting responses, which were associated with semantic overrecall and FTD.
Article
The recall of an object from features is a specific operation in semantic memory in which the thalamus and pre-supplementary motor area (pre-SMA) are integrally involved. Other higher-order semantic cortices are also likely to be involved. We used the object-recall-from-features paradigm, with more sensitive scanning techniques and larger sample size, to replicate and extend our previous results. Eighteen right-handed healthy participants performed an object-recall task and an association semantic task, while undergoing functional magnetic resonance imaging. During object-recall, subjects determined whether words pairs describing object features combined to recall an object; during the association task they decided if two words were related. Of brain areas specifically involved in object recall, in addition to the thalamus and pre-SMA, other regions included the left dorsolateral prefrontal cortex, inferior parietal lobule, and middle temporal gyrus, and bilateral rostral anterior cingulate and inferior frontal gyri. These regions are involved in semantic processing, verbal working memory and response-conflict detection and monitoring. The thalamus likely helps to coordinate activity of these different brain areas. Understanding the circuit that normally mediates this process is relevant for schizophrenia, where many regions in this circuit are functionally abnormal and semantic memory is impaired.
Article
To characterize performance on a test of semantic object retrieval (Semantic Object Retrieval Test-SORT) in healthy, elderly subjects and patients with Alzheimer disease (AD). Although the initial presentation of patients with AD often reflects impairment in delayed recall for verbally encoded memory, common complaints of patients with early AD are actually related to semantic memory impairment. Thirty-eight AD patients and 121 healthy aging controls enrolled in an Alzheimer's Disease Center received a battery of standard neuropsychologic tests including the SORT. Compared with normal controls, AD patients had SORT memory impairments with significantly more false positive memory errors, fewer correctly produced names, and more substitutions in the name production aspect of the test. SORT had robust test-retest reliability in normals. The SORT task provides a direct, specific assessment of semantic memory, and has now been administered to 121 healthy, aging controls for normative ranges of performance, and to AD patients. The task detected semantic memory deficits in approximately half of patients with mild-moderate AD, which is comparable to other studies assessing semantic deficits in AD with less specific measures.
Article
Between 10% and 15% of patients with the amnestic variety of Mild Cognitive Impairment (MCI) convert to Alzheimer disease (AD) per year. Characterize cognitive markers that may herald conversion from MCI to AD and directly assess semantic memory in patients meeting criteria for amnestic MCI. Thirty-five amnestic MCI patients and 121 healthy aging controls enrolled at an Alzheimer Disease Center received a battery of standard neuropsychologic tests, and the Semantic Object Retrieval Test (SORT), a test that we have developed for the assessment of semantic memory and subsequent name production, and that has been shown to be able to differentiate between normals and patients with AD. On the basis of normative data from the SORT, the MCI subjects could be divided into 2 groups: 10 patients (29%) with a significant semantic impairment (SI+) and 25 without a semantic memory deficit (SI-). There was a significant correlation between all SORT variables and performance on the Boston Naming Test. In this MCI population, significantly impaired SORT performance was associated with a relative decrease in performance on tests of frontal lobe functions, although disruption of thalamic-related processes cannot be excluded as an etiology for semantic memory impairment. The SORT is a specific test of semantic memory, and is a sensitive measure of semantic memory deficits in patients who otherwise meet criteria for amnestic MCI. Using this specific assessment tool, a significant number of MCI patients were found to have semantic memory deficits. As these patients may be early in the course of possible progression toward dementia, the SORT or other tests of semantic memory may provide important diagnostic or prognostic information in patients with MCI.
Article
We describe a 59-year-old woman, M.T., with a progressive language impairment and neuroimaging findings of decreased perfusion (SPECT) and focal atrophy (MRI) in the left temporal region. The most prominent feature of her cognitive profile was a profound and progressive impairment in naming. In spite of this, she performed normally on tests of semantic processing and phonological output. Her spontaneous speech was fluent with preserved syntax and articulation but with notable word-finding problems. All other cognitive abilities were relatively stable and intact. These features are not typical of either fluent or non-fluent forms of neurodegenerative language disturbance. The cognitive mechanisms that may underlie this case are discussed.
Article
Semantic memory is described as the storage of knowledge, concepts, and information that is common and relatively consistent across individuals (e.g., memory of what is a cup). These memories are stored in multiple sensorimotor modalities and cognitive systems throughout the brain (e.g., how a cup is held and manipulated, the texture of a cup's surface, its shape, its function, that is related to beverages such as coffee, and so on). Our ability to engage in purposeful interactions with our environment is dependent on the ability to understand the meaning and significance of the objects and actions around us that are stored in semantic memory. Theories of the neural basis of the semantic memory of objects have produced sophisticated models that have incorporated to varying degrees the results of cognitive and neural investigations. The models are grouped into those that are (1) cognitive models, where the neural data are used to reveal dissociations in semantic memory after a brain lesion occurs; (2) models that incorporate both cognitive and neuroanatomical information; and (3) models that use cognitive, neuroanatomic, and neurophysiological data. This review highlights the advances and issues that have emerged from these models and points to future directions that provide opportunities to extend these models. The models of object memory generally describe how category and/or feature representations encode for object memory, and the semantic operations engaged in object processing. The incorporation of data derived from multiple modalities of investigation can lead to detailed neural specifications of semantic memory organization. The addition of neurophysiological data can potentially provide further elaboration of models to include semantic neural mechanisms. Future directions should incorporate available and newly developed techniques to better inform the neural underpinning of semantic memory models.