Erbil Akbudak

University of Missouri - St. Louis, Saint Louis, Michigan, United States

Are you Erbil Akbudak?

Claim your profile

Publications (46)216.58 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Executive function (EF) and cognitive processing speed (CPS) are two cognitive performance domains that decline with advanced age. Reduced EF and CPS are known to correlate with age-related frontal-lobe volume loss. However, it remains unclear whether white matter microstructure in these regions is associated with age-related decline in EF and/or CPS. We utilized quantitative tractography metrics derived from diffusion-tensor MRI to investigate the relationship between the mean fiber bundle lengths (FBLs) projecting to different lobes, and EF/CPS performance in 73 healthy aging adults. We measured aspects of EF and CPS with the Trail Making Test (TMT), Color-Word Interference Test, Letter-Number Sequencing (L-N Seq), and Symbol Coding. Results revealed that parietal and occipital FBLs explained a significant portion of variance in EF. Frontal, temporal, and occipital FBLs explained a significant portion of variance in CPS. Shorter occipital FBLs were associated with poorer performance on the EF tests TMT-B and CWIT 3. Shorter frontal, parietal, and occipital FBLs were associated with poorer performance on L-N Seq and Symbol Coding. Shorter frontal and temporal FBLs were associated with lower performance on CPS tests TMT-A and CWIT 1. Shorter FBLs were also associated with increased age. Results suggest an age-related FBL shortening in specific brain regions related to poorer EF and CPS performance among older adults. Overall, results support both the frontal aging hypothesis and processing speed theory, suggesting that each mechanism is contributing to age-related cognitive decline.
    Brain Imaging and Behavior 11/2014; · 2.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Vascular aging consists of complex and multifaceted processes that may be influenced by genetic polymorphisms of the renin-angiotensin system. A polymorphism in the angiotensin II type 1 receptor gene (AGTR1/rs5186) has been associated with an increased risk for arterial stiffness, hypertension, and ischemic stroke. Despite these identified relationships, the impact of AGTR1 A1166C on white matter integrity and cognition is less clear in a healthy aging population. The present study utilized indices of neuroimaging and neuropsychological assessment to examine the impact of the A1166C polymorphism on subcortical hyperintensities (SH) and cognition in 49 healthy adults between ages 51-85. Using a dominant statistical model (CC + CA (risk) vs. AA), results revealed significantly larger SH volume for individuals with the C1166 variant (p < 0.05, partial eta(2) = 0.117) compared with those with the AA genotype. Post hoc analyses indicated that increased SH volume in C allele carriers could not be explained by vascular factors such as pulse pressure or body mass index. In addition, cognitive performance did not differ significantly between groups and was not significantly associated with SH in this cohort. Results suggest that presence of the C1166 variant may serve as a biomarker of risk for suboptimal brain integrity in otherwise healthy older adults prior to changes in cognition.
    Age (Dordrecht, Netherlands). 08/2014; 36(4):9664.
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the relationship between older age and mean cerebral white matter fiber bundle lengths (FBLs) in specific white matter tracts in the brain using quantified diffusion MRI.METHODS: Sixty-three healthy adults older than 50 years underwent diffusion tensor imaging. Tractography tracings of cerebral white matter fiber bundles were derived from the diffusion tensor imaging data.RESULTS: Results revealed significantly shorter FBLs in the anterior thalamic radiation for every 1-year increase over the age of 50 years.CONCLUSIONS: We investigated the effects of age on FBL in specific white matter tracts in the brains of healthy older individuals utilizing quantified diffusion MRI. The results revealed a significant inverse relationship between age and FBL. Longitudinal studies of FBL across a lifespan are needed to examine the specific changes to the integrity of white matter.
    Neurology 06/2014; · 8.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The epsilon 4 (e4) isoform of apolipoprotein E (ApoE) is a known genetic risk factor for suboptimal brain health. Morphometry studies of brains with Alzheimer's disease have reported significant alterations in temporal lobe brain structure of e4 carriers, yet it remains unclear if the presence of an e4 allele is associated with alterations in the microstructure of white matter fiber bundles in healthy populations. The present study used quantitative tractography based on diffusion tensor imaging (qtDTI) to examine the influence of the e4 allele on temporal lobe fiber bundle lengths (FBLs) in 64 healthy older adults with at least one e4 allele (carriers, N = 23) versus no e4 allele (non-carriers, N = 41). Subtests from the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) were also analyzed to examine memory performance between groups. Analyses revealed shorter FBLs in the left uncinate fasciculus (UF) (p = .038) of e4 carriers compared to non-carriers. By contrast, neither FBLs specific to the temporal lobe nor memory performances differed significantly between groups. Increased age correlated significantly with shorter FBL in the temporal lobe and UF, and with decreased performance on tests of memory. This is the first study to utilize qtDTI to examine relationships between FBL and ApoE genotype. Results suggest that FBL in the UF is influenced by the presence of an ApoE e4 allele (ApoE4) in healthy older adults. Temporal lobe FBLs, however, are more vulnerable to aging than the presence of an e4 allele.
    Brain Imaging and Behavior 03/2013; · 2.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Montreal Cognitive Assessment (MoCA) screen was developed as a brief instrument to identify mild cognitive impairment and dementia among older individuals. To date, limited information is available regarding the neuroimaging signatures associated with performance on the scale, or the relationship between the MoCA and more comprehensive cognitive screening measures. The present study examined performances on the MoCA among 111 non-clinical older adults (ages 51-85) enrolled in a prospective study of cognitive aging. Participants were administered the MoCA, Mini-Mental State Exam (MMSE), and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). A subset of participants (N = 69) underwent structural 3 T magnetic resonance imaging (MRI) to define the volumes of total frontal gray matter, total hippocampus, T2-weighted subcortical hyperintensities (SH), and total brain volume. The results revealed significant correlations between the total score on the MoCA and total score on the RBANS and MMSE, though the strength of the correlations was more robust between the MoCA and the RBANS. Modest correlations between individual subscales of the MoCA and neuroimaging variables were evident, but no patterns of shared variance emerged between the MoCA total score and neuroimaging indices. In contrast, total brain volume correlated significantly with total score on the RBANS. These results suggest that additional studies are needed to define the significance of MoCA scores relative to brain integrity among an older population.
    Archives of Clinical Neuropsychology 06/2011; 26(5):454-60. · 2.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The anterior limb of the internal capsule (ALIC) is a white matter structure, the medial portion of which includes the anterior thalamic radiation (ATR) carrying nerve fibers between thalamus and prefrontal cortex. ATR abnormalities have a possible link with cognitive abnormalities and negative symptoms in schizophrenia. We aimed to study the fiber integrity of the ATR more selectively by isolating the medial portion of the ALIC using region-of-interest based methodology. Diffusion-tensor imaging was used to measure the anisotropy of total ALIC (tALIC) and medial ALIC (mALIC) in 39 schizophrenia and 33 control participants, matched for age/gender/handedness. Relationships between anisotropy, psychopathology, and cognitive performance were analyzed. Compared with controls, schizophrenia participants had 4.55% lower anisotropy in right tALIC, and 5.38% lower anisotropy in right mALIC. There were no significant group anisotropy differences on the left. Significant correlations were observed between right ALIC integrity and relevant domains of cognitive function (e.g., executive function, working memory). Our study suggests an asymmetric microstructural change in ALIC in schizophrenia involving the right side, which is only minimally stronger in mALIC, and which correlates with cognitive impairment. Microstructural changes in the ALIC may be linked to cognitive dysfunction in schizophrenia.
    Psychiatry Research 08/2010; 183(2):144-50. · 2.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Recognition of faces/face emotions is commonly impaired in adults/children with autism. Given the importance of face processing in autism, the ability to measure face-processing pathways with DTT (Smith et.al., 2009, JMRI), and the potential of pathway abnormalities to produce strong behavioral effects, we tested for abnormalities in face-processing pathways in autism. In an initial study (Conturo et.al., 2008, JINS), the right hippocampo-fusiform (HF) pathway involved in face recognition had reduced minimum-diffusivity (D-min, intrinsic across-fiber diffusivity; Smith et.al., 2009). Objectives: Characterize/interpret DTT abnormalities in face-processing pathways by comparison to sensitive neuropsychological tests (NPTs). Methods: Custom diffusion-tensor MRI data were acquired in 17 participants with high-functioning autism meeting ADOS/ADI criteria (age 16-53) and 17 individually-matched controls from 2002-2006. For comparison, we acquired sensitive custom NPTs of: face-memory (Best et.al., IMFAR2009); face-gender identification (Wilkinson et.al., IMFAR2009); and face-emotion recognition (Rump et.al., 2009) in the autism participants. We also examined the relationship to symptom severity during development as measured by the ADI. Results: Autism participants were separated into lower/higher face-recognition subgroups using face-memory and Benton NPTs. The lower-performance subgroup had significantly slower D-min in both right HF (p = 0.019) and right amygdalo-fusiform (AF) pathway (p = 0.011). Gender/emotion NPTs showed a strong relation to DTT for both right HF/AFpathways. The DTT-NPT correlation was very high (e.g., r = 0.995/0.463 without/with one outlier; AF vs. face-gender NPT). All NPTs showed the same relation of slower D-min with lower performance for both pathways, indicating that the D-min reduction in autism-vs-controls described in (Conturo, et al., 2008) is functionally significant. The unusual reversal of the expected DTT-NPT relation supports a mechanism of small-diameter axons in right AF/HF. This interpretation parsimoniously accounts for the reversed DTT-NPT relation because small-diameter axons have slower transmission speed. This biologic mechanism is also consistent with: small cell bodies in hippocampus (Bauman et.al., 2005) and minicolumns (Casanova et.al., 2002); reduced fMRI correlations (Just et.al., 2004; Kleinhans et.al., 2008); lengthened reaction times (Townsend et.al., 1996); slowed electrophysiology (McPartland et.al., 2004); and symptom abatement with fever (Curran et.al., 2007). A correlation between ADI, Section A (reciprocal social interactions) and right HF D-min (r = -0.413; p = 0.047; slower D-min associated with childhood social impairment) suggests an early-developmental process, consistent with known impairments in face processing in young children. The D-min reduction is unlikely to be due to intervening variables (e.g., behavioral therapy) since participants do not report any consistent therapy. Any therapy effects would thus average out (and would oppose the reversed DTT-NPT relation). Finally, the high DTT-NPT correlation suggests that axonal diameter is a strong determinant of function, despite intervening variables. [More subtle secondary changes can occur in left AF/HF (Conturo et.al, 2008), consistent with relative sparing of object processing in autism (Humphreys et.al., 2008).] Conclusions: A strong association between decreased D-min and decreased function (as measured by behavioral NPTs) occurred in right AF/HF in autism, supporting a mechanism of small-diameter axons. A similar DTT-ADI relation was found, suggesting that this mechanism occurs in childhood, and persists into adulthood.
    International Meeting for Autism Research 2010; 05/2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Despite several attempts to define retinotopic maps in the macaque lateral intraparietal area (LIP) using histological, electrophysiological, and neuroimaging methods, the degree to which this area is topographically organized remains controversial. We recorded blood oxygenation level-dependent signals with functional MRI from two macaques performing a difficult visual search task on stimuli presented at the fovea or in the periphery of the visual field. The results revealed the presence of a single topographic representation of the contralateral hemifield in the ventral subdivision of the LIP (LIPv) in both hemispheres of both monkeys. Also, a foveal representation was localized in rostral LIPv rather than in dorsal LIP (LIPd) as previous experiments had suggested. Finally, both LIPd and LIPv responded only to contralateral stimuli. In contrast, human studies have reported multiple topographic maps in intraparietal cortex and robust responses to ipsilateral stimuli. These blood oxygenation level-dependent functional MRI results provide clear evidence for the topographic organization of macaque LIP that complements the results of previous electrophysiology studies, and also reveal some unexpected characteristics of this organization that have eluded these previous studies. The results also delineate organizational differences between LIPv and LIPd, providing support for these two histologically defined areas may subserve different visuospatial functions. Finally, these findings point to potential evolutionary differences in functional organization with human posterior parietal cortex.
    Proceedings of the National Academy of Sciences 02/2010; 107(10):4728-33. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To use MRI diffusion-tensor tracking (DTT) to test for the presence of unknown neuronal fiber pathways interconnecting the mid-fusiform cortex and anteromedial temporal lobe in humans. Such pathways are hypothesized to exist because these regions coactivate in functional MRI (fMRI) studies of emotion-valued faces and words, suggesting a functional link that could be mediated by neuronal connections. A total of 15 normal human subjects were studied using unbiased DTT approaches designed for probing unknown pathways, including whole-brain seeding and large pathway-selection volumes. Several quality-control steps verified the results. Parallel amygdalo-fusiform and hippocampo-fusiform pathways were found in all subjects. The pathways begin/end at the mid-fusiform gyrus above the lateral occipitotemporal sulcus bilaterally. The superior pathway ends/begins at the superolateral amygdala. The inferior pathway crosses medially and ends/begins at the hippocampal head. The pathways are left-lateralized, with consistently larger cross-sectional area, higher anisotropy, and lower minimum eigenvalue (D-min) on the left, where D-min assesses intrinsic cross-fiber diffusivity independent of curvature. A previously-undescribed pathway system interconnecting the mid-fusiform region with the amygdala/hippocampus has been revealed. This pathway system may be important for recognition, memory consolidation, and emotional modulation of face, object, and lexical information, which may be disrupted in conditions such as Alzheimer's disease.
    Journal of Magnetic Resonance Imaging 06/2009; 29(6):1248-61. · 2.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: MRI diffusion-tensor tracking (DTT) was performed in 17 high-functioning adolescents/adults with autism and 17 pairwise-matched controls. White matter pathways involved in face processing were examined due to the relevance of face perception to the social symptoms of autism, and due to known behavioral and functional imaging findings in autism. The hippocampo-fusiform (HF) and amygdalo-fusiform (AF) pathways had normal size and shape but abnormal microstructure in the autism group. The right HF had reduced across-fiber diffusivity (D-min) compared with controls, opposite to the whole-brain effect of increased D-min. In contrast, left HF, right AF, and left AF had increased D-min and increased along-fiber diffusivity (D-max), more consistent with the whole-brain effect. There was a general loss of lateralization compared with controls. The right HF D-min was markedly low in the autism subgroup with lower Benton face recognition scores, compared with the lower-Benton control subgroup, and compared with the higher-Benton autism subgroup. Similar behavioral relationships were found for performance IQ. Such results suggest an early functionally-significant pathological process in right HF consistent with small-diameter axons (with correspondingly slower neural transmission) and/or higher packing density. In left AF and HF, changes were interpreted as secondary, possibly reflecting axonal loss and/or decreased myelination.
    Journal of the International Neuropsychological Society 12/2008; 14(6):933-46. · 2.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To determine optimal conditions for precise measurement of arterial input function (AIFs) in dynamic susceptibility contrast (DSC) perfusion MRI. Magnitude-based (DeltaR(2)*) and phase-based (Deltaphi) AIFs were numerically simulated for several doses and baseline MRI noise levels [SNR(I(0))]. Random noise (1000 realizations) was added to real/imaginary MRI signals (derived from an internal carotid AIF), and AIF signal, noise, and signal-to-noise ratio (SNR) were determined. The optimal dose was defined as the dose that maximizes mean AIF SNR over the first-pass (SNR(mean)), rather than SNR at the AIF peak (SNR(peak)) because, compared to SNR(peak), doses predicted by SNR(mean) reduced the AIF-induced variability in cerebral blood flow (CBF) by 24% to 40%. The AIF SNR is most influenced by choice of AIF signal, then optimal dosing, each with little penalty. Compared to DeltaR(2)*, Deltaphi signal has 4 to 80 times the SNR over all doses and time points, and approximately 10-fold SNR(mean) at respective optimal doses. Optimal doses induce 85% to 90% signal drop for the DeltaR(2)* method, and 70% to 75% for Deltaphi, with two-fold dose errors causing approximately 1.7-fold loss in SNR(mean). Increases in SNR(I(0)) proportionally increase AIF SNR, but at a cost. AIF SNR is affected most by signal type, then dosing, and lastly, SNR(I(0)).
    Journal of Magnetic Resonance Imaging 04/2007; 25(3):598-611. · 2.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The early visual areas have a clear topographic organization, such that adjacent parts of the cortical surface represent distinct yet adjacent parts of the contralateral visual field. We examined whether cortical regions outside occipital cortex show a similar organization. The BOLD responses to discrete visual field locations that varied in both polar angle and eccentricity were measured using two different tasks. As described previously, numerous occipital regions are both selective for the contralateral visual field and show topographic organization within that field. Extra-occipital regions are also selective for the contralateral visual field, but possess little (or no) topographic organization. A regional analysis demonstrates that this weak topography is not due to increased receptive field size in extra-occipital areas. A number of extra-occipital areas are identified that are sensitive to visual field location. Neurons in these areas corresponding to different locations in the contralateral visual field do not demonstrate any regular or robust topographic organization, but appear instead to be intermixed on the cortical surface. This suggests a shift from processing that is predominately local in visual space, in occipital areas, to global, in extra-occipital areas. Global processing fits with a role for these extra-occipital areas in selecting a spatial locus for attention and/or eye-movements.
    PLoS ONE 02/2007; 2(5):e452. · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this work was to implement and assess the performance of interventions inside a cylindrical magnetic resonance imaging (MRI) scanner with an MR-compatible manipulator system and manipulator-driven real-time MR guidance. The interventional system is based on a seven degree-of-freedom MR-compatible manipulator, which offers man-in-the-loop control either with a graphical user interface or with a master/slave device. The position and the orientation of the interventional tool are sent to an MR scanner for a manipulator-driven dynamic update of the imaging plane to track, visualize and guide the motion of an end-effector. Studies on phantoms were performed with a cylindrical 1.5-T scanner using an operator-managed triggered gradient-recalled echo (GRE) or a computer-managed dynamic True Fast Imaging with Steady Precession (TrueFISP). Targets were acquired with an accuracy of 3.2 mm and with an in-plane path orientation of 2.5 degrees relative to the prescribed one. Path planning, including negotiation of obstacles and needle bending, was successfully performed. The signal-to-noise ratio (SNR) of TrueFISP was 25.3+/-2.1 when the manipulator was idle and was 18.6+/-2.4 during its operation. The SNR of triggered GRE (acquired only when the manipulator was idle) was 61.3+/-1.8. In conclusion, this study shows the feasibility of performing manually directed interventions inside cylindrical MR scanners with real-time MRI.
    Magnetic Resonance Imaging 02/2007; 25(1):69-77. · 2.06 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cerebral perfusion imaging using dynamic susceptibility contrast (DSC) has been the subject of considerable research and shows promise for basic science and clinical use. In DSC, the MRI signals in brain tissue and feeding arteries are monitored dynamically in response to a bolus injection of paramagnetic agents, such as gadolinium (Gd) chelates. DSC has the potential to allow quantitative imaging of parameters such as cerebral blood flow (CBF) with a high signal-to-noise ratio (SNR) in a short scan time; however, quantitation depends critically on accurate and precise measurement of the arterial input function (AIF). We discuss many requirements and factors that make it difficult to measure the AIF. The AIF signal should be linear with respect to Gd concentration, convertible to the same concentration scale as the tissue signal, and independent of hematocrit. Complicated relationships between signal and concentration can violate these requirements. The additional requirements of a high SNR and high spatial/temporal resolution are technically challenging. AIF measurements can also be affected by signal saturation and aliasing, as well as dispersion/delay between the AIF sampling site and the tissue. We present new in vivo preliminary results for magnitude-based (DeltaR2*) and phase-based (Deltaphi) AIF measurements that show a linearity advantage of phase, and a disparity in the scaling of Deltaphi AIFs, DeltaR2* AIFs, and DeltaR2* tissue curves. Finally, we discuss issues related to the choice of AIF signal for quantitative perfusion imaging.
    Journal of Magnetic Resonance Imaging 01/2006; 22(6):697-703. · 2.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this work is to evaluate a robotic system for remote performance of minimally invasive procedures with real-time magnetic resonance imaging (MRI) guidance inside clinical cylindrical scanners. In these studies, the operator had no physical access to the subject and used MR images and video from the observation camera in the scanner to control the robot. The control software allowed manual and semi-automated control modes and included components for collision avoidance, with the subject or the gantry of the scanner, and on-the-fly adjustment of the MR imagine plane to visualize the procedure. Studies were performed initially on phantoms and lastly on a pig inside a standard clinical cylindrical 1.5 Tesla MR scanner.
    Artificial Intelligence Applications and Innovations, 3rd IFIP Conference on Artificial Intelligence Applications and Innovations (AIAI) 2006, June 7-9, 2006, Athens, Greece; 01/2006
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A method is presented for obtaining high-sensitivity arterial input functions following bolus intravenous contrast agent administration. Arterial contrast agent is monitored by phase reconstruction of single-shot echo-planar images. During bolus injections of a gadolinium (Gd) agent in a baboon, data were acquired at the mid-abdominal aorta, and magnitude and phase-shift images were reconstructed. Pair-wise image subtraction was used to minimize phase aliasing. The phase-based method is shown to have a significant potential improvement in sensitivity compared to the magnitude approach. The phase method also has a general linear response to concentration. This method may have potential utility in quantitative imaging of blood flow and contrast agent kinetics.
    Magnetic Resonance in Medicine 12/2005; 36(6):809 - 815. · 3.27 Impact Factor
  • International Journal of Radiation OncologyBiologyPhysics 09/2004; 60. · 4.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: White matter microstructural integrity was assessed using diffusion tensor imaging (DTI) in 25 young adults, 25 nondemented older adults, and 25 age-matched older adults with dementia of the Alzheimer type (DAT). For each individual, measures of anisotropy and diffusivity were obtained from atlas-transformed images in the anterior and posterior callosum and in the frontal, parietal, temporal and occipital white matter. These data revealed age differences in anisotropy and diffusivity in all assessed regions. Age effects were greater in the anterior as opposed to the posterior corpus callosum and greater in the frontal white matter than in the temporal, parietal and occipital white matter, suggesting age-associated differences in white matter that exhibit a roughly anterior-to-posterior gradient. In contrast, individuals with early-stage dementia exhibited minimal, if any, additional change in anterior regions but did show greater deterioration of white matter in posterior lobar regions. Taken collectively, these results indicate that nondemented aging is characterized by significant changes in white matter most prominently in anterior brain regions. The dissociation between the regional effects of age and dementia status suggests that the mechanisms underlying age-associated cognitive decline are likely distinct from those underlying DAT.
    Cerebral Cortex 05/2004; 14(4):410-23. · 8.31 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The functional organization of somatosensory and motor cortex was investigated in an individual with a high cervical spinal cord injury, a 5-year absence of nearly all sensorymotor function at and below the shoulders, and rare recovery of some function in years 6-8 after intense and sustained rehabilitation therapies. We used functional magnetic resonance imaging to study brain activity to vibratory stimulation and voluntary movements of body parts above and below the lesion. No response to vibratory stimulation of the hand was observed in the primary somatosensory cortex (SI) hand area, which was conversely recruited during tongue movements that normally evoke responses only in the more lateral face area. This result suggests SI reorganization analogous to previously reported neuroplasticity changes after peripheral lesions in animals and humans. In striking contradistinction, vibratory stimulation of the foot evoked topographically appropriate responses in SI and second somatosensory cortex (SII). Motor cortex responses, tied to a visuomotor tracking task, displayed a near-typical topography, although they were more widespread in premotor regions. These findings suggest possible preservation of motor and some somatosensory cortical representations in the absence of overt movements or conscious sensations for several years after spinal cord injury and have implications for future rehabilitation and neural-repair therapies.
    Proceedings of the National Academy of Sciences 01/2003; 99(26):17066-71. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Braille reading depends on remarkable adaptations that connect the somatosensory system to language. We hypothesized that the pattern of cortical activations in blind individuals reading Braille would reflect these adaptations. Activations in visual (occipital-temporal), frontal-language, and somatosensory cortex in blind individuals reading Braille were examined for evidence of differences relative to previously reported studies of sighted subjects reading print or receiving tactile stimulation. Nine congenitally blind and seven late-onset blind subjects were studied with fMRI as they covertly performed verb generation in response to reading Braille embossed nouns. The control task was reading the nonlexical Braille string "######". This study emphasized image analysis in individual subjects rather than pooled data. Group differences were examined by comparing magnitudes and spatial extent of activated regions first determined to be significant using the general linear model. The major adaptive change was robust activation of visual cortex despite the complete absence of vision in all subjects. This included foci in peri-calcarine, lingual, cuneus and fusiform cortex, and in the lateral and superior occipital gyri encompassing primary (V1), secondary (V2), and higher tier (VP, V4v, LO and possibly V3A) visual areas previously identified in sighted subjects. Subjects who never had vision differed from late blind subjects in showing even greater activity in occipital-temporal cortex, provisionally corresponding to V5/MT and V8. In addition, the early blind had stronger activation of occipital cortex located contralateral to the hand used for reading Braille. Responses in frontal and parietal cortex were nearly identical in both subject groups. There was no evidence of modifications in frontal cortex language areas (inferior frontal gyrus and dorsolateral prefrontal cortex). Surprisingly, there was also no evidence of an adaptive expansion of the somatosensory or primary motor cortex dedicated to the Braille reading finger(s). Lack of evidence for an expected enlargement of the somatosensory representation may have resulted from balanced tactile stimulation and gross motor demands during Braille reading of nouns and the control fields. Extensive engagement of visual cortex without vision is discussed in reference to the special demands of Braille reading. It is argued that these responses may represent critical language processing mechanisms normally present in visual cortex.
    Journal of Neurophysiology 02/2002; 87(1):589-607. · 3.30 Impact Factor

Publication Stats

6k Citations
216.58 Total Impact Points

Institutions

  • 2011–2013
    • University of Missouri - St. Louis
      • Department of Psychology
      Saint Louis, Michigan, United States
  • 1996–2013
    • Washington University in St. Louis
      • • Department of Physics
      • • Department of Radiology
      San Luis, Missouri, United States
  • 2009
    • University of Kentucky
      • Department of Neurology
      Lexington, KY, United States
  • 1997–2002
    • University of Washington Seattle
      • Department of Neurological Surgery
      Seattle, WA, United States
  • 1998
    • St. Luke's Hospital (MO, USA)
      Saint Louis, Michigan, United States