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Gabriella Eördegh
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ABSTRACT: The main differences between the geniculate and the ascending tectal/extrageniculate visual systems are the presence of multisensory units and the absence of the strict retinotopical organization in the tectal system.
To investigate the coding of the visual and multisensory information in the tectal system, and to clarify the direction of visual information flow between the extrastriate cortex along the anterior ectosylvian sulcus and the lateral medialis-suprageniculate nucleus of the posterior thalamus.
Extracellular single-cell recordings were carried out in anesthetized, immobilized cats to visual and multisensory stimulation.
The thalamo-cortical route seems to have a dominant role in the bidirectional information flow between the LM-Sg and the AES cortex. The panoramic neurons in the AES cortex and the LM-Sg may code in their discharge rate the site of the spatial visual and multisensory information and exhibited multisensory cross-modal integration.
Our results demonstrate the existence of a distributed population code of spatial multisensory information in the tectal visual system.
Orvosi Hetilap 08/2009; 150(30):1413-20.
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ABSTRACT: Despite extensive analysis of the motor functions of the basal ganglia and the fact that multisensory information processing appears critical for the execution of their behavioral action, little is known concerning the sensory functions of the caudate nucleus (CN) and the substantia nigra (SN). In the present study, we set out to describe the sensory modality distribution and to determine the proportions of multisensory units within the CN and the SN. The separate single sensory modality tests demonstrated that a majority of the neurons responded to only one modality, so that they seemed to be unimodal. In contrast with these findings, a large proportion of these neurons exhibited significant multisensory cross-modal interactions. Thus, these neurons should also be classified as multisensory. Our results suggest that a surprisingly high proportion of sensory neurons in the basal ganglia are multisensory, and demonstrate that an analysis without a consideration of multisensory cross-modal interactions may strongly underrepresent the number of multisensory units. We conclude that a majority of the sensory neurons in the CN and SN process multisensory information and only a minority of these units are clearly unimodal.
Acta Biologica Hungarica 10/2008; 59(3):269-79. · 0.59 Impact Factor
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ABSTRACT: The spatio-temporal frequency response profiles of 73 neurons located in the superficial, retino-recipient layers of the feline superior colliculus (SC) were investigated. The majority of the SC cells responded optimally to very low spatial frequencies with a mean of 0.1 cycles/degree (c/deg). The spatial resolution was also low with a mean of 0.31 c/deg. The spatial frequency tuning functions were either low-pass or band-pass with a mean spatial frequency bandwidth of 1.84 octaves. The cells responded optimally to a range of temporal frequencies between 0.74 cycles/s (c/s) and 26.41 c/s with a mean of 6.84 c/s. The majority (68%) of the SC cells showed band-pass temporal frequency tuning with a mean temporal frequency bandwidth of 2.4 octaves, while smaller proportions of the SC units displayed high-pass (19%), low-pass (8%) or broad-band (5%) temporal tuning. Most of the SC units exhibited simple spectral tuning with a single maximum in the spatio-temporal frequency domain, while some neurons were tuned for spatial or temporal frequencies or speed tuned. Further, we found cells excited by gratings moving at high temporal and low spatial frequencies and cells whose activity was suppressed by high velocity movement. The spatio-temporal filter properties of the SC neurons show close similarities to those of their retinal Y and W inputs as well as those of their inputs from the cortical visual motion detector areas, suggesting their common role in motion analysis and related behavioral actions.
Experimental Brain Research 08/2007; 181(1):87-98. · 2.39 Impact Factor
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ABSTRACT: Sensorimotor co-ordination in mammals is achieved predominantly via the activity of the basal ganglia. To investigate the underlying multisensory information processing, we recorded the neuronal responses in the caudate nucleus (CN) and substantia nigra (SN) of anaesthetized cats to visual, auditory or somatosensory stimulation alone and also to their combinations, i.e. multisensory stimuli. The main goal of the study was to ascertain whether multisensory information provides more information to the neurons than do the individual sensory components. A majority of the investigated SN and CN multisensory units exhibited significant cross-modal interactions. The multisensory response enhancements were either additive or superadditive; multisensory response depressions were also detected. CN and SN cells with facilitatory and inhibitory interactions were found in each multisensory combination. The strengths of the multisensory interactions did not differ in the two structures. A significant inverse correlation was found between the strengths of the best unimodal responses and the magnitudes of the multisensory response enhancements, i.e. the neurons with the weakest net unimodal responses exhibited the strongest enhancement effects. The onset latencies of the responses of the integrative CN and SN neurons to the multisensory stimuli were significantly shorter than those to the unimodal stimuli. These results provide evidence that the multisensory CN and SN neurons, similarly to those in the superior colliculus and related structures, have the ability to integrate multisensory information. Multisensory integration may help in the effective processing of sensory events and the changes in the environment during motor actions controlled by the basal ganglia.
European Journal of Neuroscience 09/2006; 24(3):917-24. · 3.63 Impact Factor
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ABSTRACT: This study describes the visual information coding ability of single neurons in the suprageniculate nucleus (Sg), and provides new data concerning the visual information flow in the suprageniculate/anterior ectosylvian pathways of the feline brain. The visual receptive fields of the Sg neurons have an internal structure rather similar to that described earlier in the anterior ectosylvian visual area (AEV). The majority of the Sg units can provide information via their discharge rate at the site of the visual stimulus within their large receptive fields. This suggests that they may serve as panoramic localizers. The sites of maximum responsivity of the Sg neurons are distributed over the whole investigated part of the visual field. There is no significant difference between the distributions of spatial location of maximum sensitivity of the AEV and the Sg neurons. The mean visual response latency of the Sg units was found to be significantly shorter than the mean latency of the AEV neurons, but there was no difference between the shortest latency values of the thalamic and the cortical single-units. This suggests that the visual information flows predominantly from the Sg to the AEV, though the cortico-thalamic route is also active. The Sg seems to represent a thalamic nucleus rather similar in function to both the first-order relays and the higher-order thalamic nuclei. These results, together with the fact that the superior colliculus provides the common ascending source of information to the suprageniculate/anterior ectosylvian pathway, suggest a unique function of the AEV and the Sg in sensorimotor integration.
Brain Research Bulletin 11/2005; 67(4):281-9. · 2.82 Impact Factor
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ABSTRACT: This study describes a possible mechanism of coding of multisensory information in the anterior ectosylvian visual area of the feline cortex. Extracellular microelectrode recordings on 168 cells were carried out in the anterior ectosylvian sulcal region of halothane-anaesthetized, immobilized, artificially ventilated cats. Ninety-five neurons were found to respond to visual stimuli, 96 responded to auditory stimuli and 45 were bimodal, reacting to both visual and auditory modalities. A large proportion of the neurons exhibited significantly different responses to stimuli appearing in different regions of their huge receptive field. These neurons have the ability to provide information via their discharge rate on the site of the stimulus within their receptive field. This suggests that they may serve as panoramic localizers. The ability of the bimodal neurons to localize bimodal stimulus sources is better than any of the unimodal localizing functions. Further, the sites of maximal responsivity of the visual, auditory and bimodal neurons are distributed over the whole extent of the large receptive fields. Thus, a large population of such panoramic visual, auditory and multisensory neurons could accurately code the locations of the sensory stimuli. Our findings support the notion that there is a distributed population code of multisensory information in the feline associative cortex.
European Journal of Neuroscience 08/2004; 20(2):525-9. · 3.63 Impact Factor
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ABSTRACT: The pedunculopontine tegmental nucleus (PPT) projects its cholinergic fibers to both the lateralis medialis-suprageniculate nucleus (LM-Sg) and the superior colliculus (SC). For the purpose of verification of whether a single neuron in the PPT projects to both the LM-Sg and the SC, we injected dextran tetramethylrhodamine (DR) into the LM-Sg and dextran fluorescein (DF) into the ipsilateral SC. The DR-positive neurons labeled retrogradely in the PPT are small (mean: 27.13+/-1.22 micro m) and distributed in the rostral two-thirds of this nucleus, whereas the DF-positive neurons are small (mean: 27.54+/-1.16 micro m) or medium-sized (mean: 40.18+/-1.43 micro m), and are located throughout the PPT. Thirty-five percent of all labeled neurons are double-labeled and small. The present study indicates that the PPT projection to the LM-Sg in part involves neurons bifurcating to the SC.
Experimental Brain Research 05/2004; 155(4):421-6. · 2.39 Impact Factor
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ABSTRACT: Visual single-unit activity was recorded in the caudate nucleus of halothane-anaesthetized, immobilized, artificially respirated cats. Visually sensitive neurons were found in the dorsolateral part of the caudate body. A majority of the units responded optimally to small spot-like stimuli moving with velocities between 30 and 120 degrees /s. The receptive field of these units is large: it covers a major part of both the contra- and ipsilateral visual hemifields. No signs of retinotopy were observed. Most of the neurons display directional selectivity and are narrowly tuned to the direction of the moving stimulus. These physiological properties are consistent with recent morphological results that reveal multiple connections of the caudate nucleus with the superior colliculus through tecto-extrageniculo-thalamic pathways in the mammalian brain.
European Journal of Neuroscience 08/2003; 18(2):449-52. · 3.63 Impact Factor
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ABSTRACT: The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 75 neurons of the feline anterior ectosylvian visual area (AEV). Extracellular single-unit recordings were performed in halothane-anesthetized (0.6%), immobilized, artificially ventilated cats. Most cells were strongly sensitive to the direction of drifting gratings. The mean value of the direction tuning widths was approximately 90 deg. Most of the cells (69 of the 75 cases) displayed rather narrowly tuned band-pass characteristics in the low spatial frequency range, with a mean optimal spatial frequency of 0.2 cycles/degree (c/deg). The mean spatial bandwidth was 1.4 octaves. The remainder of the units was low-pass tuned. A majority of the units responded optimally to high temporal frequencies (mean 6.3 Hz), although some cells did exhibit preferences for every examined temporal frequency between 0.6 Hz and 10.8 Hz. The temporal frequency-tuning functions mostly revealed a band-pass character with a mean temporal bandwidth of 1.1 octaves. Our results demonstrate that the neurons along the anterior ectosylvian sulcus display particular spatial and temporal characteristics. The AEV neurons, with their preference for low spatial frequencies and with their fine spatial and temporal tuning properties, seem to be candidates for special tasks in motion perception.
Experimental Brain Research 08/2003; 151(1):108-14. · 2.39 Impact Factor
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ABSTRACT: Extracellular microelectrode recordings were carried out on 150 neurons in the anterior ectosylvian sulcal region of halothane-anesthetized, immobilized, artificially ventilated cats. Fifty-nine neurons were visual, 60 were auditory and 31 were bimodal visual-auditory. As the extent of the receptive fields has never been exactly determined, we introduced a quasi-objective, computer-based, statistical method in order to estimate the receptive field sizes in the anterior half of the perimeter. The visual, auditory and bimodal cells had very large receptive fields, often with portions extending well into the ipsilateral hemifield. The mean extents of the visual and auditory receptive fields in the horizontal plane were 75.75 degrees (N=59, SD: +/- 28.620, range: 15-135 degrees), and 132.5 degrees (N=60, SD: +/- 46.72 degrees, range: 15-165 degrees) respectively. These data suggest that a single visual neuron can carry information from the whole visual field of the right eye and a single auditory unit can carry information of azimuths throughout the whole area of the horizontal plane studied. The mean extent of the bimodal receptive fields in the horizontal plane was 82.1 degrees (N=31, SD: +/- 24.24 degrees, range: 30-135 degrees). In 21 of the 31 bimodal cells we observed a facilitatory interaction between visual and auditory stimuli. The mean extent of the facilitatory interactions in these cells was 75.75 degrees (N=21, SD: +/- 24.56 degrees, range: 45-135 degrees).
Acta Physiologica Hungarica 02/2003; 90(4):305-12. · 0.82 Impact Factor
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ABSTRACT: Élettani és anatómiai vizsgálataink egy olyan új koncepció bizonyítására irányulnak, mely szerint a szenzoros információ feldolgozása egymással párhuzamosan, egymástól többé-kevésbé függetlenül futó csatornákon/pályákon/áramlatokon keresztül valósul meg. A pályázat végrehajtása során altatott, immobilizált macskák agyában extracelluláris egysejt-tevékenységet regisztráltunk, valamint nyomkövető anyagokkal pályaanalízist végeztünk. Emellett éber, viselkedő majmok inferotemporális kérgében regisztráltunk egysejtaktivitást a képfelismerés élettani folyamatainak tisztázására. A vizsgálatok más része pszichiátriai, neurológiai vagy szemészeti kórképekben szenvedő embereken történt. Leírtuk, hogy a bazális ganglionok két magjában (nucleus caudatus és substantia nigra) levő sejtek klasszikus receptív mező tulajdonságai megfelelnek az általunk korábban leírt tecto-thalamo-corticalis multimodalis pályarendszer neuronjainak élettani sajátságaival. Morfológiai eredményeink összegzése és az élettani adatokkal történő összevetése alkalmat nyújt arra, hogy egy multimodalis szenzoros információfeldolgozó modellt állítsunk össze, mely a bazális ganglionok szenzoros bemenetének újszerű szemléletét szolgáltatja. A makákó majom inferotemporalis kérgi sejtjei egységtevékenységének mérése lehetővé tette a vizuális asszociatív funkció és percepciós neuronális működés összevetését is. | Our physiological and anatomical experiments were aimed at verifying a novel concept in sensory information processing. This concept implies that sensory information is processed through parallel, more or less independent channels/pathways/streams. We recorded extracellular single-unit activity in the brain of anaesthetized, immobilized cats and analyzed sensory pathways employing various tracers. In addition to this, single-unit activity was recorded in the inferotemporal cortex of awake, restrained monkeys in order to clarify the physiological processes during perception. Other experiments were performed in psychiatric, neurological and ophthalmologic patients. Our most important finding was that we proved the classical receptive field properties of some basal ganglia (caudate nucleus and substantia nigra) correspond to the physiological properties of neurons in the tecto-thalamo-cortical multimodal pathway described by us during the last 25 years. Integration of our morphological data with the results of physiological experiments allowed us to construct a novel model of sensory information processing that suggest the sensory input towards the basal ganglia being of tectal origin. The analysis of neuronal activity in the inferotemporal cortex of monkeys allowed a comparison of visual associative function and neuronal activity. In our clinical investigations we analyzed the consequences of selective pathway lesions in various disease forms.
