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Notes: Summary We have analysed, in the awake monkey (Macaca sylvana) the functional properties of 489 neurones in the prelunate visual area (PVA, largely corresponding to V4). PVA has a coarse retinotopic organization with the lower quadrant of the visual field represented along the prelunate gyrus. The visual periphery is located medio-dorsally, the central visual field laterally near (and within?) the inferior occipital sulcus and the upper quadrant latero-ventrally. The vertical meridian runs caudally within the lunate sulcus, the horizontal meridian crosses the prelunate gyrus and continues into the superior temporal sulcus. Receptive field diameters of neurones vary between 1° and 10° with increase towards the visual periphery, but are strictly confined to the contralateral visual field. 28% of the neurones showed spectral sensitivity. About half of these cells had strong spectral opponency, the other half showed only weak opponency with broader spectral response curves. 11 cells (2%) showed striking centre/surround interactions with inhibition, disinhibition or occlusion of the two mechanisms, and different spectral response ranges of the centre and the surround, respectively. 43% of the prelunate cells were responsive to various spatial features without spectral sensitivity. We distinguished on- and off-center cells (2%), direction and movement sensitive cells (10%) and cells sensitive to gratings of parallel lines within a limited range of orientations (about 10%). A special group were cells which responded strongly to stimuli which contained many contrasts (textures without specific orientations and without regular spatial arrangements) (9%). Many of these cells were specifically responsive to variations of the internal structure of such stimuli. 3% of the cells were strongly activated in connection with behaviour: 11 neurones discharged strongly when the monkey looked attentively at a human face or when he responded with facial expressions to a threatening expression of a person. Photographs of faces were not effective. Some neurones (1%) were activated in connection with eye movement. These neurones were found in the lateral part of the prelunate gyrus. Neurones with spectral or non-spectral properties were clustered within small, irregularly shaped patches of 1–4 mm diameter. It is concluded that the prelunate visual cortex, which we consider as part of area 19, is not just a “colour area”, but represents various features of the visual environment (including colour, luminance, movement, texture and behavioral significance), and relates them — through its subcortical and cortical outputs — to behaviour. The various visual cortical areas may be seen as a cooperative of several connections between visual input and behaviour output rather than as links in a hierarchical chain of perceptual and cognitive representations.

Notes: Summary The representation of the hand and fingers in area 1 of the first somatosensory cortex was studied in conscious monkeys by recording single neuronal activity. The results are as follows. (1) We found multi-finger type receptive fields which cover more than one finger discontinuously or wide-field type ones which cover both finger and palmar skin or two halves of the palmar skin together. Multi-finger type receptive fields were also found in some joint manipulation neurons. Multifinger or wide-field type receptive fields were found in nearly 40% of area 1 neurons. The rate was even higher, up to 70%, in the medial part of the cortical finger region. Consequently, the finger representation in area 1 was less discretely somatotopic than that in area 3b. (2) The submodality content of area 1 was almost identical to that of area 3b: 74.5% and 20.9% of identified neurons were, respectively, cutaneous and deep. The distribution of neurons with different submodalities overlapped in area 1. (3) Among area 1 neurons with multi-finger type receptive fields, response characteristics of those with inhibitory receptive fields, those with directional selectivity to moving stimuli, and those with converging afferent inputs, were studied in detail. Evidence is presented to suggest that information from different parts of the body, or from the same body parts but different afferent sources, is integrated in area 1. (4) It is proposed that, within the SI, area 1 is the initial stage of integration of sensory information coming from the thalamus and from area 3a or 3b via cortico-cortical connections.

Notes: Summary The representation of fingers in the first somatosensory cortex was studied in conscious monkeys by recording single neuronal activity, and the following results were obtained: (1) In area 3a, most neurons responded to joint manipulation or other types of deep stimuli. The representation of five fingers was somatotopically arranged. (2) In area 3b, 77.7% and 20.9% of identified neurons responded to cutaneous and deep stimuli respectively. (3) Neurons responding to light mechanical stimuli and with receptive fields on the distal finger segment were found in the most anterior part of area 3b while those responding better to specific mechanical stimuli, such as rubbing, scraping, pinching, tapping, etc. of finger glabrous skin, were found in the more posterior part. The representation of the five fingers was somatotopically arranged. (4) Neurons responding to light or specific mechanical stimulation of the dorsal hairy skin of fingers were found in the posterior part of area 3b. The independent somatotopic representation of four fingers was recognized within this region. (5) Neurons responding to mechanical stimulation of the palmar skin were found in two separate regions, the medial one for the ulnar half and the lateral one for the radial half of the palm. (6) These results indicate that the representation of fingers in areas 3a and 3b of the conscious monkey is divided into multiple somatotopic subdivisions each representing a functional region of the hand and fingers. (7) Neurons with multi-finger receptive fields were occasionally found in area 3b, mostly in layer VI. Some of them had inhibitory receptive fields. Multifinger type receptive fields were more commonly found in area 1.

Notes: Summary Single neuronal activity was recorded in the crown of the postcentral gyrus (areas 1 and 2) in 5 conscious monkeys. A total of 93 penetrations were made in the hand and finger region of 9 hemispheres and 827 neurons were isolated. The receptive field characteristics of neurons recorded along each of 88 penetrations which entered perpendicularly to the cortical surface were compared. The majority of neurons in this region were responsive to skin stimulation. In 54 penetrations, neurons related to different sensory submodalities were mixed. In 30, skin neurons predominated, and in 8, ‘deep’ neurons, while in the remaining 16 penetrations neurons related to different submodalities were equally mixed. In 16 penetrations, neurons responded exclusively to stimulation of skin, hair or nails. In 9 penetrations, neurons were exclusively related to joint manipulation or other types of ‘deep’ submodality. In 9 penetrations, unidentified neurons were in the majority. In each penetration, the receptive field positions varied considerably on the same finger or encompassed more than one finger. Although neurons of the same submodality, either skin or ‘deep’ tended to be set in an array, the most adequate stimulus could vary among neurons of a given array. The variability in the receptive field positions or the most adequate stimuli remained constant irrespective of the angle of the electrode penetration in the cortex. The results are compatible with the idea that vertically arranged neuronal array receive inputs of multiple sources, both thalamacortical and corticocortical, so that interactions between different inputs can readilly occur.

Notes: Summary We have recorded from 661 single neurons in the foveal and parafoveal region of area 17 of the awake trained macaque monkey. The functional properties of 538 cells were investigated in detail, with flashed and moving stimuli of varying form and colour. Irrespective of their functional properties such determined, each neuron was also tested with a 2×2° square of various luminance and colour. This was done in order to get an idea how such a simple stimulus is represented by the activities of neurons in area 17. Most of the neurons showed response preference for certain aspects of visual stimuli. We have distinguished the following functional groups: 1. Sustained spectrally selective neurons (21%). These cells respond with tonic discharges to light of their optimal wavelength, and their spectral selectivity corresponded to that of opponent parvocellular cells of the lateral geniculate body. 44% of these cells were excited selectively by long, 23% by middle and 33% by short wavelength light. When slowly moving the 2×2° square of their preferred wavelength across the receptive field, discharge rate remained elevated, as long as the stimulus covered the RF and with little contour enhancement. The majority of the sustained spectrally sensitive cells responded equally well or better to large than to small (1.0°) stimuli, 17.5% were less activated and few of them completely suppressed by larger stimuli. Such cells were poorly orientation sensitive. Only three cells with weak double opponency could be identified (2.7% of this group). 2. Broadband contour (18%) and 3. Panchromatic contour cells (41%). Most neurons of these two groups were strongly activated by spots (1°) centered on their RF. They showed a short phasic response to contrast borders and most of them responded to luminance contrasts, including contrast reversal and colour contrasts equated for luminance. The broadband contour cells showed a slight wavelength preference with only weak or without any opponent suppression, the panchromatic contour neurons did not show any wavelength selectivity. Most showed orientation or direction sensitivity, but very sharp orientation selectivity was less common in spectrally biassed than in panchromatic contour cells (see Fig. 11). They responded tonically to gratings of optimal orientation and therefore may play a role also for cortical representation of textures. 22% of a restricted sample of panchromatic contour cells (or 9% of all cells) were hypercomplex. 4. Light inhibited cells. 7% of all cells were inhibited by small and large light stimuli of any wavelength centered on their receptive field, and were tonically activated by darkspots or contrasts, comparable to the light inhibited cells of the parvocellular lateral geniculate layers. 5. Neurons without consistant visual responses (11%). These neurons could not be driven by any of our visual stimuli. They were usually found in the upper cortical layers. 61 cells were tested for monocular vs. binocular input. 96% were excited from both eyes with various degrees of ocular dominance, but more binocular cells were contralaterally than ipsilaterally dominated (43 and 22%, respectively). Binocular cells showed qualitatively the same functional properties from both eyes, including spectral selectivity if there was any. Binocular summation varied between cells and was in the average 0.7, probably due to interocular inhibition. Some columnar grouping of cells with similar response properties as defined above was found in vertical penetrations, but “mixed” penetrations were common. Spectrally selective cells with the same spectral preference or light inhibited cells often were found close to each other and in the same penetration, but also often mixed with other cells excited by parvocellular input. This spatial organization is consistant with a columnar segregation of cells excited predominantly by one type of parvocellular afferents on the one hand, and contour cells with a mixed excitatory and a strong inhibitory input, on the other hand, but also indicates a considerable mixing and overlap of functional inputs into any axis perpendicular to the cortical surface. The functional organization of area 17 is compared with that of the lateral geniculate body and the prelunate visual area (V4) as investigated with the same methods and by the same laboratory.