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Hemianopia induced by unilateral visual cortex lesions can be resolved by repeatedly exposing the blinded hemifield to auditory–visual stimuli. This rehabilitative “training” paradigm depends on mechanisms of multisensory plasticity that restore the lost visual responsiveness of multisensory neurons in the ipsilesional superior colliculus (SC) so that they can once again support vision in the blinded hemifield. These changes are thought to operate via the convergent visual and auditory signals relayed to the SC from association cortex (the anterior ectosylvian sulcus [AES], in cat). The present study tested this assumption by cryogenically deactivating ipsilesional AES in hemianopic, anesthetized cats during weekly multisensory training sessions. No signs of visual recovery were evident in this condition, even after providing animals with up to twice the number of training sessions required for effective rehabilitation. Subsequent training under the same conditions, but with AES active, reversed the hemianopia within the normal timeframe. These results indicate that the corticotectal circuit that is normally engaged in SC multisensory plasticity has to be operational for the brain to use visual–auditory experience to resolve hemianopia.

Two main types of cortical terminals have been identified in the cat thalamus. Large (type II) have been proposed to drive the response properties of thalamic cells while smaller (type I) are believed to modulate those properties. Among the cat’s visual cortical areas, the anterior ectosylvian visual area (AEV) is considered as one of the highest areas in the hierarchical organization of the visual system. Whereas the connections from the AEV to the thalamus have been recognized, their nature (type I or II) is presently not known. In this study, we assessed and compared the relative contribution of type I and type II inputs to thalamic nuclei originating from the AEV. The anterograde tracer BDA was injected in the AEV of five animals. Results show that (1) both type I and II terminals from AEV are present in the Lateral Posterior- Pulvinar complex, the lateral median suprageniculate complex and the medial and dorsal geniculate nuclei (2) type I terminals significantly outnumber the type II terminals in almost all nuclei studied. Our results indicate that neurons in the AEV are more likely to modulate response properties in the thalamus rather than to determine basic organization of receptive fields of thalamic cells.

Crossmodal plasticity is the phenomenon whereby, following sensory damage or deprivation, the lost sensory function of a brain region is replaced by one of the remaining senses. One of several proposed mechanisms for this phenomenon involves the expansion of a more active brain region at the expense of another whose sensory inputs have been damaged or lost. This territorial expansion hypothesis was examined in the present study. The cat ectosylvian visual area (AEV) borders the auditory field of the anterior ectosylvian sulcus (FAES), which becomes visually reorganized in the early-deaf. If this crossmodal effect in the FAES is due to the expansion of the adjoining AEV into the territory of the FAES after hearing loss, then the reorganized FAES should exhibit connectional features characteristic of the AEV. However, tracer injections revealed significantly different patterns of cortical connectivity between the AEV and the early-deaf FAES, and substantial cytoarchitectonic and behavioral distinctions occur as well. Therefore, the crossmodal reorganization of the FAES cannot be mechanistically attributed to the expansion of the adjoining cortical territory of the AEV and an overwhelming number of recent studies now support unmasking of existing connections as the operative mechanism underlying crossmodal plasticity.

Previous work has established that the spatial receptive fields (SRFs) of multisensory neurons in the cerebral cortex are strikingly heterogeneous, and that SRF architecture plays an important deterministic role in sensory responsiveness and multisensory integrative capacities. The initial part of this contribution serves to review these findings detailing the key features of SRF organization in cortical multisensory populations by highlighting work from the cat anterior ectosylvian sulcus (AES). In addition, we have recently conducted parallel studies designed to examine SRF architecture in the classic model for multisensory studies, the cat superior colliculus (SC), and we present some of the preliminary observations from the SC here. An examination of individual SC neurons revealed marked similarities between their unisensory (i.e., visual and auditory) SRFs, as well as between these unisensory SRFs and the multisensory SRF. Despite these similarities within individual neurons, different SC neurons had SRFs that ranged from a single area of greatest activation (hot spot) to multiple and spatially discrete hot spots. Similar to cortical multisensory neurons, the interactive profile of SC neurons was correlated strongly to SRF architecture, closely following the principle of inverse effectiveness. Thus, large and often superadditive multisensory response enhancements were typically seen at SRF locations where visual and auditory stimuli were weakly effective. Conversely, subadditive interactions were seen at SRF locations where stimuli were highly effective. Despite the unique functions characteristic of cortical and subcortical multisensory circuits, our results suggest a strong mechanistic interrelationship between SRF microarchitecture and integrative capacity.

Absztrakt A várandós anyák primer és rekurrens humán cytomegalovirus- (HCMV-) fertőzéséhez társulhat a magzat fertőzése. A HCMV a congenitalis fertőzések leggyakoribb okozója, amelynek legsúlyosabb következményei a szellemi visszamaradottság, progrediáló halláskárosodás, látászavarok. Az anya primer fertőzését követi leggyakrabban a magzat fertőzése, és a magzat károsodásai rendszerint súlyosak. Növekszik az anyai rekurrens fertőzések után jelentkező, különböző súlyosságú tünetekkel járó congenitalis HCMV-fertőzések száma. Az aktív HCMV-fertőzéssel komplikált terhességek gondozásában döntő szerepet játszik a praenatalis diagnosztika. A congenitalis HCMV-fertőzés potenciálisan súlyos következményei ellenére kevés adat áll rendelkezésünkre a HCMV vertikális terjedésének antivirális gyógyszerrel történő megelőzésére, de a passzív immunizálással biztató eredmények vannak. Vakcina hiányában is elkerülhető a várandós anyák aktív HCMV-fertőzése, ha felhívjuk a figyelmet a fertőzés veszélyeire és ismertetjük a fertőzés megelőzésének lehetőségeit.

Converging cortical influences from the anterior ectosylvian sulcus and the rostral lateral suprasylvian sulcus were shown to have a multisensory-specific role in the integration of sensory information in superior colliculus (SC) neurons. These observations were based on changes induced by cryogenic deactivation of these cortico-SC projections. Thus, although the results indicated that they played a critical role in integrating SC responses to stimuli derived from different senses (i.e., visual–auditory), they played no role in synthesizing its responses to stimuli derived from within the same sense (visual–visual). This was evident even in the same multisensory neurons. The results suggest that very different neural circuits have evolved to code combinations of cross-modal and within-modal stimuli in the SC, and that the differences in multisensory and unisensory integration are likely caused by differences in the configuration of each neuron's functional inputs rather than to any inherent differences among the neurons themselves. The specificity of these descending influences was also apparent in the very different ways in which they affected responses to the component cross-modal stimuli and their actual integration. Furthermore, they appeared to target only multisensory neurons and not their unisensory neighbors.

1. Neurons that are selectively sensitive to the direction of motion of elongated contours have been found in several cortical areas in many species. However, in the striate cortex of the cat and monkey, and the extrastriate posteromedial lateral suprasylvian visual area of the cat, such cells are generally component motion selective, signaling only the direction of movement orthogonal to the preferred orientation; a direction that is not necessarily the same as the motion of the entire pattern or texture of which the cell's preferred contour is part. The primate extrastriate middle temporal area is the only cortical region currently known to contain a substantial population of pattern-motion-selective cells that respond to the shared vector of motion of mixtures of contours. 2. From analyzing published data on the connectivity of the cat's cortex, we predicted that the anterior ectosylvian visual area (AEV), situated within the anterior ectosylvian sulcus, might be a higher-order motion processing area and thus likely to contain pattern-motion-selective neurons. This paper presents the results of a study on neuronal responses in AEV. 3. Ninety percent of AEV cells that responded strongly to drifting grating and/or plaid stimuli were directionally selective (directionality index > 0.5). For this group, the mean directionality index was 0.75. Moreover, 55% of these cells were unequivocally classified as pattern motion selective and only one neuron was classified as definitely component motion selective. Thus high-level pattern motion coding occurs in the cat extrastriate cortex and is not limited to the primate middle temporal area. 4. AEV contains a heterogeneous population of directionally selective cells. There was no clear relation between the degree of directional selectivity for plaids or gratings and the degree of selectivity for pattern motion or component motion. Nevertheless, 28% of the highly responsive cells were both more strongly modulated by plaids than gratings and more pattern motion selective than component motion selective. Such cells could correspond to a population of "selection units" signaling the salience of local motion information. 5. AEV lacks global retinotopic order but the preferred direction of motion of neurons (rather than axis of motion, as in the middle temporal area and the posteromedial lateral suprasylvian visual area) is mapped systematically across the cortex. Our data are compatible with AEV being a nonretinotopic, feature-mapped area in which cells representing similar parts of "motion space" are brought together on the cortical sheet.

It has recently been demonstrated that the maturation of normal multisensory circuits in the cortex of the cat takes place over an extended period of postnatal life. Such a finding suggests that the sensory experiences received during this time may play an important role in this developmental process. To test the necessity of sensory experience for normal cortical multisensory development, cats were raised in the absence of visual experience from birth until adulthood, effectively precluding all visual and visual–nonvisual multisensory experiences. As adults, semichronic single-unit recording experiments targeting the anterior ectosylvian sulcus (AES), a well-defined multisensory cortical area in the cat, were initiated and continued at weekly intervals in anesthetized animals. Despite having very little impact on the overall sensory representations in AES, dark-rearing had a substantial impact on the integrative capabilities of multisensory AES neurons. A significant increase was seen in the proportion of multisensory neurons that were modulated by, rather than driven by, a second sensory modality. More important, perhaps, there was a dramatic shift in the percentage of these modulated neurons in which the pairing of weakly effective and spatially and temporally coincident stimuli resulted in response depressions. In normally reared animals such combinations typically give rise to robust response enhancements. These results illustrate the important role sensory experience plays in shaping the development of mature multisensory cortical circuits and suggest that dark-rearing shifts the relative balance of excitation and inhibition in these circuits.

Although there are many perceptual theories that posit particular maturational profiles in higher-order (i.e., cortical) multisensory regions, our knowledge of multisensory development is primarily derived from studies of a midbrain structure, the superior colliculus. Therefore, the present study examined the maturation of multisensory processes in an area of cat association cortex [i.e., the anterior ectosylvian sulcus (AES)] and found that these processes are rudimentary during early postnatal life and develop only gradually thereafter. The AES comprises separate visual, auditory, and somatosensory regions, along with many multisensory neurons at the intervening borders between them. During early life, sensory responsiveness in AES appears in an orderly sequence. Somatosensory neurons are present at 4 weeks of age and are followed by auditory and multisensory (somatosensory–auditory) neurons. Visual neurons and visually responsive multisensory neurons are first seen at 12 weeks of age. The earliest multisensory neurons are strikingly immature, lacking the ability to synthesize the cross-modal information they receive. With postnatal development, multisensory integrative capacity matures. The delayed maturation of multisensory neurons and multisensory integration in AES suggests that the higher-order processes dependent on these circuits appear comparatively late in ontogeny.

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.

The majority of multisensory neurons in the cat superior colliculus (SC) are able to synthesize cross-modal cues (e.g., visual and auditory) and thereby produce responses greater than those elicited by the most effective single modality stimulus and, sometimes, greater than those predicted by the arithmetic sum of their modality-specific responses. The present study examined the role of corticotectal inputs from two cortical areas, the anterior ectosylvian sulcus (AES) and the rostral aspect of the lateral suprasylvian sulcus (rLS), in producing these response enhancements. This was accomplished by evaluating the multisensory properties of individual SC neurons during reversible deactivation of these cortices individually and in combination using cryogenic deactivation techniques. Cortical deactivation eliminated the characteristic multisensory response enhancement of nearly all SC neurons but generally had little or no effect on a neuron's modality-specific responses. Thus, the responses of SC neurons to combinations of cross-modal stimuli were now no different from those evoked by one or the other of these stimuli individually. Of the two cortical areas, AES had a much greater impact on SC multisensory integrative processes, with nearly half the SC neurons sampled dependent on it alone. In contrast, only a small number of SC neurons depended solely on rLS. However, most SC neurons exhibited dual dependencies, and their multisensory enhancement was mediated by either synergistic or redundant influences from AES and rLS. Corticotectal synergy was evident when deactivating either cortical area compromised the multisensory enhancement of an SC neuron, whereas corticotectal redundancy was evident when deactivation of both cortical areas was required to produce this effect. The results suggest that, although multisensory SC neurons can be created as a consequence of a variety of converging tectopetal afferents that are derived from a host of subcortical and cortical structures, the ability to synthesize cross-modal inputs, and thereby produce an enhanced multisensory response, requires functional inputs from the AES, the rLS, or both.

The receptive field properties of 131 visual neurons lying along the anterior ectosylvian sulcus were studied with extracellular recordings in barbiturate-anaesthetized, immobilised, artificially ventilated cats. A stationary visual noise pattern was presented in an area of 24x32 degrees, in which an 8x8 degrees portion moved randomly at a speed of 10 deg/s. A definite best area characterized by maximal firing rate was found, from where the firing rate declined monotonously towards the periphery of the receptive field. The best area locations were distributed in a 40x40 degrees region around the area centralis. These results seem to verify a rather robust capacity in AEV neurones for stimulus localization, in spite of their immense receptive fields.

Visual and auditory sensory responses of cortical neurons in the caudal half of the anterior ectosylvian sulcus (AES) of cats were examined under α-chloralose anesthesia, using intracellular recording and labeling techniques. Stable intracellular recordings were obtained from 155 neurons, and 141 neurons exhibited responses to sensory stimuli. Of 141 sensory neurons, 74 (52%) were bimodal neurons that responded to both visual and auditory stimuli, and 67 (48%) were unimodal showing sensory responses only to visual (25) or auditory stimulation (42). Forty-five neurons (35 pyramidal neurons, 5 non-pyramidal neurons, 5 not classified) responsive to sensory stimuli were labeled with biocytin. The percentage of bimodal neurons of the biocytin-labeled neurons was 40% ( 4 10 ) in layer II, 50% ( 10 20 ) in layer III–IV, 70% ( 7 10 ) in layer V and 60%/) ( 3 5 ) in layer VI. Thus the convergence of visual and auditory inputs on single neurons was most intense in layer V. Auditory response latencies were in a narrow range from 10 to 40 ms, whereas visual response latencies were in a wide range from 15 to 100 ms. Late visual responses (> 60 ms) were more commonly elicited in bimodal neurons than in visual unimodal neurons. Visual responses in layer 11 were all elicited over 40 ms, whereas early visual responses within 40 ms were observed in the other cortical layers. A subgroup of neurons ( 22 141 ) had a propensity to exhibit a burst discharge, a train of three to seven action potentials on a deploarizing envelope in response to sensory stimuli. Their specific distribution in cortical tissue was suggested by the result that six out of nine biocytin-labeled neurons (seven pyramidal neurons, two non-pyramidal neurons) showing burst discharges to sensory stimuli were observed in layer V. These results are considered to signify some aspects of intracortical organization related to the cross-modal integration of sensory inputs.

We inserted microelectrodes in eye movement-evoking cortices (EMECs) of cats and examined whether neurones in the EMECs received sensory input from guide signals and fired prior to saccades. The five EMECs were the medial wall of the hemisphere under the cruciate sulcus, the medical and lateral bank of the presylvian sulcus, the fundus of the coronal sulcus and ventral bank of the anterior ectosylvian sulcus. Neurones in all EMECs responded to input guide signals and discharged prior to the saccades. The neurones, however, did not always respond to all saccades, but responded cooperatively or alternatively among the EMECs. These results suggest that input information is projected to a broad area of the cortex and is integrated with output signals in the same cortex to which the input information was projected.

The anatomical pathways supplying the visual signal to the cat orbito-insular cortex (OIC) from primary visual areas were studied by an anterograde axonal transport technique. L-[5-3H]proline was injected, in different animals, in each of areas 17, 18, 19 and the lateral suprasylvian visual area (LS). Serial histological sections were processed by autoradiographic technique after long (8-16 days) or short (30 h) survival times. The axonal flow labelled direct pathways from LS to the ipsilateral orbital gyrus and the ventral bank of the anterior ectosylvian sulcus; this region seems to correspond to that from which many authors recorded photically evoked potentials. Long survival animals injected in LS showed labels also in the contralateral OIC. No axonal flow could be demonstrated from areas 17, 18 and 19 to OIC, either at short of long survival times. The results suggest that, apart from possible sub cortical afferences, a critical visual input may reach OIC from the extrageniculostriate visual system through LS. The functional relevance of extrastriate input to OIC is discussed.

In this paper a cortical area is described that covers approximately the posterior two-thirds of the ventral bank of the anterior ectosylvian sulcus of the cat and is called anterior ectosylvian visual area (AEV). In cats anesthetized with a combination of N2O and barbiturate we explored this area by recording extracellularly the responses of AEV neurons to visual and electric stimulation as well as by injecting HRP into physiologically verified points. AEV neurons were found to be highly sensitive to small light stimuli moving rapidly in a particular direction through their large receptive fields. The properties of 74 neurons were quantitatively analyzed. Increasing the length of the stimulus within the receptive field to more than 2 deg strongly inhibited the responses, whereas increasing the speed of the stimulus movement up to 72-120 deg/s enhanced the neuronal responsiveness. Although the majority of neurons responded to a wide range of possible directions, one clearly preferred direction could usually be found for each neuron. There was predominance of preferred directions toward the contralateral hemifield. Anatomic and electrophysiologic connectivity studies showed that AEV receives its main afferent inputs from the lateral suprasylvian visual area (LS) and from the tecto-pulvinar complex. Although these studies suggested some topographical organization within the projection from LS to AEV, the large receptive fields in AEV, the great majority of which included the central area, did not reveal a clear retinotopic order. It is concluded that AEV is a specific visual area and that functionally the extrageniculate inputs predominate.

A 'new' and orderly representation of the body surface was found in the cerebral cortex of the cat. This somatotopic map was located in the anterior ectosylvian sulcus (AES), an area known to represent several modalities, but believed to be distinguished from primary sensory cortex by its lack of sensory topographies. Auditory and visual cells were also found in the AES, but were not randomly intermixed with the somatic representation. These data, coupled with those from previous studies strongly suggest the necessity for a revision of the traditional distinctions between cortical regions.

Microelectrode mapping techniques were employed in the cat's auditory cortex to relate the best frequencies of a large population of neurons with their spatial loci. Based upon the best-frequency distribution, the auditory region was divided into four complete and orderly tonotopic representations and a surrounding belt of cortex in which the tonotopic organization was more complex. The four auditory fields occupy a crescent-shaped band of tissue which comprises portions of both the exposed gyral surfaces and sulcal banks of the ectosylvian cortex. The anterior auditory field (A) is situated most rostrally upon the anterior ectosylvian gyrus. It extends upon the ventral bank of the suprasylvian sulcus and upon the banks of the anterior ectosylvian sulcus. Adjoining field A caudally is the primary auditory field (AI), which extends across the middle ectosylvian gyrus and portions of both banks of the posterior ectosylvian sulcus. The representations of the highest best frequencies in fields A and AI are contiguous. Caudal and ventral to AI are located the posterior (P) and ventroposterior (VP) auditory fields. They lie mainly upon the caudal bank of the posterior ectosylvian sulcus but also extend upon the rostral bank and upon the posterior ectosylvian gyrus. The low best-frequency representations of fields AI and P are contiguous, whereas the low best-frequency representation of field VP lies near the ventral end of the posterior ectosylvian sulcus. Fields P and VP are joined along their middle and high best-frequency representations. Within each auditory field isofrequency lines defined by the spatial loci of neurons with similar best frequencies are oriented orthogonal to the low-to-high best-frequency gradients.

Within and near the rostral half of the anterior ectosylvian gyrus of an unanesthetized chronic cat, properties of units which responded to stimulation of the ipsilateral upper canine tooth pulp were studied. In total 75 responsive units were recorded by 192 microelectrode penetrations. Discharge patterns of these units to pulp stimulation were classified into 3 types: single spike response (4 units), short burst response (66 units) and prolonged response continuing up to several hundred msec (4 units). Spontaneous activities of one exceptional unit were depressed for 200-300 msec after pulp stimulation. These units were scattered in the explored cortical area, indicating that the SII somatotopically organized area may also receive nociceptive inputs. Most of these units responded to some modalities of mechanical stimuli applied to various parts of the body surface including face and head. This result suggests that they may correspond to the neurons unspecific with regard to modality and place observed in the anesthetized cat. Few units activated by pulp stimulation were encountered in the rostral portion of the anterior ectosylvian gyrus, where MELZACK and HAUGEN (1957) recorded the evoked potential by pulp stimulation. Five tooth pulp-sensitive units which were excited only by pin pricks and/or firm pressure were encountered on the dorsal bank of the anterior ectosylvian sulcus, the non-somatotopically organized area of SII.

We recorded from single neurons in both banks of the posterior two-thirds of the anterior ectosylvian sulcus. All neurons were tested with visual and tactile stimulations. In each bank of the anterior ectosylvian sulcus the majority of neurons were bimodal, i.e. responded to both visual and tactile stimuli (B cells); the remaining population was strictly unimodal, responding either to visual (V cells) or to somatosensory (T cells) stimulation. Bimodal and unimodal neurons were recorded at all explored cortical sites and were consistently intermixed. Unlike bimodal neurons, unimodal neurons showed an asymmetric localization: the V cells were significantly more numerous in the ventral bank while the T neurons were preferentially found in the dorsal bank of the sulcus. We could not detect an orderly somatotopic or visuotopic representation, nor was it possible to find a systematic spatial correspondence between somatic and visual receptive fields. The functional organization of the anterior ectosylvian cortex is discussed in terms of a hierarchical processing of sensory information.

We report electrophysiological data regarding the contribution of the corpus callosum to visual responses in the cortex around the anterior ectosylvian sulcus (AES). The experiments were performed in cats in which the optic input from each eye was surgically restricted to the ipsilateral hemisphere (split-chiasm cats), and where neuronal responses to stimulation of the contralateral eye were mediated by interhemispheric connections. A very high proportion of cells were driven by stimuli presented to either eye indicating that they were activated not only through an intrahemispheric pathway from the ipsilateral eye, but also through an interhemispheric pathway from the contralateral eye. With few exceptions, both receptive fields (RFs) of each binocular neuron abutted or were in the vicinity of the vertical meridian. All neurons responded well to moving stimuli and most of them showed directional selectivity. A few cells were activated by stimuli moving in depth. Following an additional section of the posterior half of the corpus callosum, cells in AES responded only to stimulation of the ipsilateral eye, demonstrating thus that the input from the contralateral eye was conveyed by this part of the corpus callosum. By contrast following a section of the anterior half of the corpus callosum, all visually responsive AES neurons were binocularly activated. These results suggest that the interhemispheric visual input to this ectosylvian region is conveyed via a polysynaptic loop involving visual cortical areas that are connected through the posterior portion of the corpus callosum.

The corticocortical connections of the frontal 'oculomotor' areas related to eye movements of the cat were studied using the retrograde horseradish peroxidase (HRP) tracing method combined with electrophysiological techniques. The following results were obtained. (1) The medial wall of the hemisphere under the cruciate sulcus (CRU), where contralateral conjugate eye deviation was elicited, received fibers from the medial bank of the presylvian sulcus (PRE). The fundus of the coronal sulcus (COR), where monocular movement of the contralateral eye was evoked, received fibers from the lateral bank of the PRE. (2) All the frontal oculomotor areas, the medial wall of the hemisphere under the CRU, the fundus of the COR, and both banks of the PRE, received fibers from the ipsilateral ventral bank of the anterior ectosylvian sulcus (AES). (3) The ventral bank of the AES received fibers from the caudal part of the lateral suprasylvian visual areas. On the basis of the fiber connections, the frontal oculomotor areas can be subdivided into a 'medial' area, the medial wall of the hemisphere under the CRU and the medial bank of the PRE, and a 'lateral' area, the lateral bank of the PRE and the fundus of the COR. Moreover, we found evidence of fiber projections from the ventral bank of the AES to the frontal oculomotor areas that were physiologically identified.

The auditory response properties of single neurons in the fundus and banks of the anterior ectosylvian sulcus (AES) were studied with simple dichotic stimuli (viz. noise- and tone-bursts) in cats anaesthetized with alpha-chloralose. Neurons within AES showed simple onset responses, were most commonly excited by stimulation of both ears, and showed either broad tuning or multiple high best frequencies. Some neurons were also tested for visual responsiveness and it was found that auditory cells and visual cells were intermingled within the sulcus. A small percentage of cells responded to both auditory and visual stimulation. Overall, the response properties of AES neurons differed from those of nearby auditory cortical fields. The region of AES studied appears to be outside the recently defined fourth somatosensory area (SIV), but overlaps para-SIV found deeper in the sulcus. It appears that deep within the sulcus and along most of its length there is a population of auditory, somatosensory and visual cells; to delineate this auditory population from the surrounding auditory cortical fields this region has been designated Field AES.

Electrical stimulation of the fastigial nucleus provoked surface-negative field potentials bilaterally in the cerebral cortical regions around the anterior ectosylvian sulcus (AES) in the cat anesthetized with pentobarbital. Laminar field potential analysis revealed that the active locus for the negative potentials is located within the cortical layer I of the lower bank of the AES, i.e. the insular cortex.

Following injections of horseradish peroxidase conjugated with wheatgerm agglutinin (HRP-WGA) in different sectors of the cortex of the anterior ectosylvian sulcus (SEsA), anterograde labeling was observed in the pontine nuclei (PN) of the cat. Labeled fibers were identified in a wide area which covers the entire rostro-caudal extent of the PN. The various sectors of the SEsA, which differ in their associative, corticocortical connections with the somatosensory, auditory and visual cortices, also were shown to differ in their projection patterns to the PN. These corticopontine projections of the SEsA were compared to those from the modality specific areas.

Axonal projections from cells in cortex surrounding the caudal part of the anterior ectosylvian sulcus (AES) to the superior colliculus (SC) were examined using anterograde tracers. The projection terminates in the medial two-thirds of the deep layers of SC bilaterally, and appears to be topographically organized, perhaps according to the sensory modality (auditory and visual) represented in the caudal part of AES.