Maria Grazia Maioli

Projections from visual cortical areas of the superior temporal sulcus to the lateral terminal nucleus of the accessory optic system in macaque monkeys.

Tritiated amino acids were injected into the striate area and in single visual areas of the superior temporal sulcus (STS) of 7 cynomolgus monkeys, in order to trace visual cortical projections to the nuclei of the accessory optic system (AOS). Injections in STS separately involved the areas MT and MST, and resulted in labels within the lateral terminal nucleus of the AOS. In no case were labels found within the AOS nuclei in the brains injected in the striate area, or within the contralateral AOS. It seems likely that the areas MT and MST contribute signals--selectively related to visual motion processing--to the AOS, which is probably involved in the neuronal pathway subserving the optokinetic reflex.

'Real-motion' cells in the primary visual cortex of macaque monkeys.

Extracellular recordings were carried out in the primary visual cortex of behaving macaque monkeys. Neurons were activated by moving a visual stimulus across their receptive fields during periods of steady fixation and by moving their receptive fields (by visual tracking) across a motionless visual stimulus, taking care that the velocities of stimulus and eye movements were the same. The total cell population (108 neurons) ws divided into 3 groups according to the cell sensitivity to visual stimulus orientation (non-oriented cell and oriented cells) and to the presence or absence of antagonistic areas in in the receptive fields (oriented cells with antagonistic areas). All the non-oriented cells (n = 14) showed almost the same response to visual stimulation both during steady fixation and during visual tracking. Out of a total number of 86 oriented cells, 77 turned out to be activated by the visual stimulation both during fixation and tracking. Eight oriented cells gave a very weak response or no response at all to visual stimulation during smooth pursuit eye movements and one neuron of the same group showed a greater response during visual tracking than during fixation. Six out of 8 oriented cells with antagonistic areas showed almost the same response to the two types of visual stimulation, while the remaining two neurons showed very weak responses during smooth pursuit eye movements. Our results show that a small percentage (about 10%) of striate neurons in macaque monkeys gave very different responses to the same physical stimulation at retinal level, according to the presence or absence of slow eye movements (smooth pursuit eye movements). The activity of these neurons seems to be related to the real movement of something in the visual world, in spite of the retinal image movement per se.

Cortico-cortical connections from the visual region of the superior tempora sulcus to frontal eye field in the macaque

Abstract Injections of tritiated amino acids were made in the posterior bank and the fundus of the caudal third of the superior temporal sulcus (STs) of macaque monkeys. The injection sites lay mainly within the heavily myelinated region of STs, namely the middle temporal area. Labelled material was found in the surface of the caudal-most part of the prearcuate gyrus and in the anterior bank of the arcuate sulcus, that is in a restricted region of the part of the prefrontal cortex known as frontal eye field (FEF). The possibility that FEF may include several functional units receiving different visual inputs is considered.

Bilateral projections from the visual cortex to the striatum in the cat

SummaryDirect projections from visual areas 17, 18, 19, and lateral suprasylvian visual area (LS) to the striatum were searched for in 12 adult cats using the autoradiographic technique to detect neuronal pathways. Striatal labels were found only after injections in areas 19 and LS. Projections homolateral to the injection sites were observed from both areas to the head and body of the caudate nucleus and to the putamen. Contralateral projections were found from both areas 19 and LS: however, area 19 did not project to the contralateral putamen. The extent of contralateral projections was smaller and they were confined within the same regions as the homolateral ones. Silver grains were often arranged in cluster-like patches, which were more evident ipsilaterally, in the head of the caudate nucleus and after injections in area LS.The present data support the view of a not strictly topographical segregation of striatal projections from the cat visual cortex.

Corticocortical connections between frontal periarcuate regions and visual areas of the superior temporal sulcus and the adjoining inferior parietal lobule in the macaque monkey

In macaque monkeys, corticocortical connections between distinct parietotemporal visual areas (areas MST-FST, DP, and 7a) and frontal periarcuate areas are studied using tritiated aminoacids and WGA-HRP. While labeling within the banks of the principal sulcus, the dorsal part of the arcuate concavity, and the banks of the upper arcuate limb were present in both 7a and MST-FST injected animals; in the latter cases, additional projections were found towards frontal regions including the dorsomedial frontal cortex and the posterior bank of the arcuate ventral limb. Our results point to widespread frontal connections of the MST-FST complex, involving both prefrontal and premotor cortical regions.

Maintained activity of single neurons in striate and non-striate areas of the cat visual cortex

Abstract A study was made of the spontaneous impulse activity generated by single neural elements in striate and non-striate areas of the cat visual cortex in a state of assumed steady conditions. Microelectrode recordings were made using the technique of the closed chamber, under continuous control of several physiological parameters. The maintained activity of each neuron was examined by considering the mean firing rate and the interspike intervals. Neurons in areas 17 and 18 show similar discharge frequencies (6–7 spikes/sec), whereas neurons in area 19 display a lower frequency (2.76 spikes/sec) of discharge. The interspike interval analysis shows that the spontaneous activity of neurons in areas 18 and 19 is different from that in area 17 for its dominating pattern (grouped activity) of spike discharge. This pattern, whenever present, is responsible for the L-shape shown by the histogrammatic representation of these intervals. Therefore, neurons of area 18, although they have a firing rate similar to that of striate neurons, show with respect to the latter a different pattern of activity. Neurons of area 19 are closer to cells of area 18 than to those of area 17. An analysis of the relation between mean firing rate and cortical depth led to the conclusion that the discharge frequency of a cortical visual neuron is a probable function of cell size. When tested for the property of independence on systematic factors, the spontaneous activity of neurons of the visual cortex turned out to be dependent in 81% of the units ( N = 124). Examination of the units in different layers of the visual cortex showed that the percentage of dependent cells is somewhat lower in deep than in superficial layers. The differential and common properties of neurons of striate and non-striate areas of the visual cortex were examined in some detail and are commented upon.

Cortical visual input to the orbito-insular cortex in the cat

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.

Gaze and smooth pursuit signals interact in parietal area 7m of the behaving monkey.

Posterior parietal cortex is a region specialized for multimodal integration and coordinate transformations which converts sensory input to motor output. Eye position signals are crucial for such transformations, because they are needed to the inner reconstruction of a stable image of the outside world in spite of eye movements. Area 7m is a parietal area anatomically connected with oculomotor structures such as frontal eye field and superior colliculus. The aim of this study was to assess if neurons in area 7m possess activity related to eye movements, and if so, which sort of movements are processed. We recorded the extracellular activity of 7m neurons in two monkeys trained in both a smooth pursuit and a visually guided saccade task. The majority of neurons tested with the smooth pursuit task (16/17) showed directional selectivity influenced by the eye position. Moreover, these neurons were tuned to inward or outward pursuit with respect to the center of extra-personal visual space. About half of the cells (11/24) tested with the saccade task changed their activity during the pre-saccadic period. The majority of neurons presented post-saccadic activity: most of the cells showed a directionally-selective phasic response and a modulation by eye position during fixation (23/24). Overall, we observed that area 7m contains a population of neurons signaling smooth pursuit direction at certain eye position and saccade direction toward specific portions of the visual space. We hypothesize that area 7m might be involved in spatial map updating which can be used for spatial orientation.

Chapter 26: Some extra-striate corticothalamic connections in macaque monkeys

Publisher Summary This chapter describes some corticothalamic connections of the middle temporal (MT) area and the neighbouring, MT-recipient, visual region situated in the fundus and upper bank of superior temporal sulcus (STS) of the macaque monkey. These connections turned out to be part of a parallel network reciprocally linking sensory structures to cortical and subcortical formations that, from anatomical and electrophysiological investigations, appear to be involved in the neural control of directionally oriented eye movements, as well as in the orientation of visual attention. In the macaque monkey, the caudal half of the STS is an important cortical station of the extrageniculo-striate visual system in which discrete visual areas have been identified. Among these, the MT area is reputed to play a key role in visual motion analysis because of the property of its neurons to selectively respond to the direction and speed of moving visual stimuli. Areas surrounding MT are less defined as to their anatomical limits, connections, and functions. The pieces of evidence highlighted in this chapter suggest that the extrageniculo-striate corticothalamic system involving the superior temporal cortex is an intimate part of a complex network of functional units.

Maintained activity of single neurons in the cat visual cortex at different levels of retinal adaptation

The influence of ambient illumination on the maintained electrical activity of single neurons of the cat visual cortex was studied by using the closed chamber technique for extracellular recordings. Several levels of light background within the scotopic-mesopic range were explored. Phasic and tonic changes in firing rate were observed following a background change. The former were irregular and unpredictable variations lasting up to 15-20 min. The latter, which usually followed the phasic changes, showed the constant characteristic of being in direct relation to luminance variations for neurons isolated in the striate area and in inverse relation for units recorded from the two non-striate areas of the visual cortex; in all cases, they lasted until a new luminous level was set. Changes in firing rate were not dependent upon either the neuron receptive field organization or the EEG pattern, simultaneously recorded. The background-locked firing rate variations recorded at the visual cortex seem to be the result of a particular cortical distribution of afferent fibers carrying luminance information. Applications to vision research are also suggested.