Salvatore Squatrito

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.

Projections from the visual cortex to the contralateral claustrum of the cat revealed by an anterograde axonal transport method

Contralateral projections from visual areas 17, 18, 19 and the Clare-Bishop area of the cerebral cortex to the claustrum have been investigated in the cat using intracortical injections of [3H]proline. Radioactive material was found in a dorsocaudal region of the contralateral claustrum. This region was homotopic with respect to that found for the ipsilateral projection from visual cortex. The contralateral connection is assumed to be a monosynaptic pathway. The pattern by which the corticofugal fibres terminate in the claustrum is quite similar to the one described for the opposite hemisphere [6].

Autoradiographic evidence for projections from cortical visual areas 17, 18, 19 and the Clare-Bishop area to the ipsilateral claustrum in the cat

Projections from different visual areas of the cerebral cortex to the ipsilateral claustrum have been investigated in the cat by intracortical injections of [3H]proline. As a consequence of axonal flow an accumulation of radioactive material within a dorso-caudal region of the ipsilateral claustrum was found. The proline-transporting terminal arborizations of projections from areas 17, 18, 19 and the Clare-Bishop area overlap in the same claustral region. No point-to-point relation was observed between any one visual area and its claustral projection. Differences in the terminal distribution pattern were detectable according to the visual areas of origin.

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.

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.

Functional and anatomical profile of visual motion impairments in stroke patients correlate with fMRI in normal subjects

We used six psychophysical tasks to measure sensitivity to different types of global motion in 45 healthy adults and in 57 stroke patients who had recovered from the initial results of the stroke, but a large subset of them had enduring deficits on selective visual motion perception tasks. The patients were divided into four groups on the basis of the location of their cortical lesion: occipito-temporal, occipito-parietal, rostro-dorsal parietal, or frontal-prefrontal. The six tasks were: direction discrimination, speed discrimination, motion coherence, motion discontinuity, two-dimensional form-from-motion, and motion coherence - radial. We found both qualitative and quantitative differences among the motion impairments in the four groups: patients with frontal lesions or occipito-temporal lesions were not impaired on any task. The other two groups had substantial impairments, most severe in the group with occipito-parietal damage. We also tested eight healthy control subjects on the same tasks while they were scanned by functional magnetic resonance imaging. The BOLD signal provoked by the different tasks correlated well with the locus of the lesions that led to impairments among the different tasks. The results highlight the advantage of using psychophysical techniques and a variety of visual tasks with neurological patients to tease apart the contribution of different cortical areas to motion processing.

Response Time, Visual Search Strategy, and Anticipatory Skills in Volleyball Players

This paper aimed at comparing expert and novice volleyball players in a visuomotor task using realistic stimuli. Videos of a volleyball setter performing offensive action were presented to participants, while their eye movements were recorded by a head-mounted video based eye tracker. Participants were asked to foresee the direction (forward or backward) of the setters toss by pressing one of two keys. Key-press response time, response accuracy, and gaze behaviour were measured from the first frame showing the setters hand-ball contact to the button pressed by the participants. Experts were faster and more accurate in predicting the direction of the setting than novices, showing accurate predictions when they used a search strategy involving fewer fixations of longer duration, as well as spending less time in fixating all display areas from which they extract critical information for the judgment. These results are consistent with the view that superior performance in experts is due to their ability to efficiently encode domain-specific information that is relevant to the task.

Visual Search Strategy in Judo Fighters during the Execution of the First Grip

Visual search behaviour is believed to be very relevant for athlete performance, especially for sports requiring refined visuo-motor coordination skills. Modern coaches believe that optimal visuo-motor strategy may be part of advanced training programs. Gaze behaviour of expert and novice judo fighters was investigated while they were doing a real sport-specific task. The athletes were tested while they performed a first grip either in an attack or defence condition. The results showed that expert judo fighters use a search strategy involving fewer fixations of longer duration than their novice counterparts. Experts spent a greater percentage of their time fixating on lapel and face with respect to other areas of the scene. On the contrary, the most frequently fixed cue for novice group was the sleeve area. It can be concluded that experts orient their gaze in the middle of the scene, both in attack and in defence, in order to gather more information at once, perhaps using parafoveal vision.