Saccadic influences on single neuron activity in the medial bank of the cat's suprasylvian sulcus (Clare Bishop area)

The functions of the proprioceptors of the eye muscles

This article sets out to present a fairly comprehensive review of our knowledge about the functions of the receptors that have been found in the extraocular muscles--the six muscles that move each eye of vertebrates in its orbit--of all the animals in which they have been sought, including Man. Since their discovery at the beginning of the 20th century these receptors have, at various times, been credited with important roles in the control of eye movement and the construction of extrapersonal space and have also been denied any function whatsoever. Experiments intended to study the actions of eye muscle receptors and, even more so, opinions (and indeed polemic) derived from these observations have been influenced by the changing fashions and beliefs about the more general question of how limb position and movement is detected by the brain and which signals contribute to those aspects of this that are perceived (kinaesthesis). But the conclusions drawn from studies on the eye have also influenced beliefs about the mechanisms of kinaesthesis and, arguably, this influence has been even larger than that in the converse direction. Experimental evidence accumulated over rather more than a century is set out and discussed. It supports the view that, at the beginning of the 21st century, there are excellent grounds for believing that the receptors in the extraocular muscles are indeed proprioceptors, that is to say that the signals that they send into the brain are used to provide information about the position and movement of the eye in the orbit. It seems that this information is important in the control of eye movements of at least some types, and in the determination by the brain of the direction of gaze and the relationship of the organism to its environment. In addition, signals from these receptors in the eye muscles are seen to be necessary for the development of normal mechanisms of visual analysis in the mammalian visual cortex and for both the development and maintenance of normal visuomotor behaviour. Man is among those vertebrates to whose brains eye muscle proprioceptive signals provide information apparently used in normal sensorimotor functions; these include various aspects of perception, and of the control of eye movement. It is possible that abnormalities of the eye muscle proprioceptors and their signals may play a part in the genesis of some types of human squint (strabismus); conversely studies of patients with squint in the course of their surgical or pharmacological treatment have yielded much interesting evidence about the central actions of the proprioceptive signals from the extraocular muscles. The results of experiments on the eye have played a large part in the historical controversy, now in at least its third century, about the origin of signals that inform the brain about movement of parts of the body. Some of these results, and more of the interpretations of them, now need to be critically re-examined. The re-examination in the light of recent experiments that is presented here does not support many of the conclusions confidently drawn in the past and leads to both new insights and fresh questions about the roles of information from motor signals flowing out of the brain and that from signals from the peripheral receptors flowing into it. There remain many lacunae in our knowledge and filling some of these will, it is contended, be essential to advance our understanding further. It is argued that such understanding of eye muscle proprioception is a necessary part of the understanding of the physiology and pathophysiology of eye movement control and that it is also essential to an account of how organisms, including Man, build and maintain knowledge of their relationship to the external visual world. The eye would seem to provide a uniquely favourable system in which to study the way in which information derived within the brain about motor actions may interact with signals flowing in from peripheral receptors. The review is constructed in relatively independent sections that deal with particular topics. It ends with a fairly brief piece in which the author sets out some personal views about what has been achieved recently and what most immediately needs to be done. It also suggests some lines of study that appear to the author to be important for the future.

The role of the lateral suprasylvian visual cortex of the cat in object-background interactions: permanent deficits following lesions

The contribution of the lateral suprasylvian cortex to pattern recognition was studied by behavioural detection experiments in combination with bilateral lesions of different parts of the lateral suprasylvian areas (LSA) and area 7 in seven cats. In a two-alternatives forced choice task the cats had to discriminate simple outline patterns which were additively superimposed on a structured visual background made up of broadband Gaussian noise. For various stimulus conditions (moving or stationary patterns and/or background) the detection probability (PD) of the cats was measured as a function of the signal-to-noise ratio (S/N). Each cat was tested before and after the lesion. Four different types of lesion could be distinguished depending on their extent: (1) lesion of parts of the (LSA); (2) lesion of parts of the LSA with undercutting of areas 17, 18 and 19; (3) lesion of area 7; (4) lesion of area 7 and parts of the LSA. 1. We found that a large bilateral lesion of the LSA led to significant deficits in all test situations which were dependent on the existence of relative velocity of moving patterns against a structured background. The ability of the cats to discriminate simple outline patterns which were kept stationary was not reduced. On the contrary, when they were tested with stationary and moving patterns on unfocused (empty) backgrounds, we found, to our great surprise, that the performance of the lesioned cats was significantly improved compared with intact animals. As these lesioned cats had no deficits with moving patterns on a uniformly grey background, we conclude that the deficits with the moving patterns must have been caused by interactions between patterns and background, and not by movement of a pattern per se. 2. As soon as the lesion of the LSA was extended by a bilateral undercutting of areas 17, 18 and 19 we found very severe deficits in all test situations, regardless of whether the patterns were moving or kept stationary, or whether they were superimposed on a background or not. The most substantial deficits occurred when the patterns were moving on a stationary background. In these situations the cats were no longer able to reach the 84% correct criterion. Again, the cats were able to reach criterion with moving patterns on a uniformly grey background indicating that this deficit is probably caused by the interaction of patterns and background and not by motion of the patterns per se.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional roles of the lateral suprasylvian cortex in ocular near response in the cat

The lateral suprasylvian (LS) area, an extrastriate visual area in the cat, has been suggested to play an important role in processing motion in 3-dimensional visual space. In addition, the LS area is related to all three components of the ocular near response, i.e. lens accommodation, pupillary constriction, and ocular convergence: microstimulation in this area evoked these intra- and extraocular movements, and neuronal discharges associated with these movements were also found. Anatomical pathways, direct and indirect, from this area to premotor nuclei in the brainstem are known to exist. The present paper reviews studies useful for assessing the functional roles played by the LS area in triggering and modulating component movements in the ocular near response.

Disjunctive eye movement evoked by microstimulation in an extrastriate cortical area of the cat

Slow disjunctive eye movement similar to ocular convergence was evoked by microstimulation in parts of the lateral suprasylvian area (LSA) in alert cats. A tungsten-in-glass microelectrode was used for stimulation, and eye movement was monitored using the magnetic search coil method. The velocity-versus-amplitude relationship of disjunctive eye movement evoked by microstimulation was comparable to that of ocular convergence evoked by presenting a visual target. It is suggested that the LSA plays a role in controlling convergence eye movement.

Cortical control of oculomotor functions. I. Optokinetic nystagmus

The cortical control of horizontal optokinetic nystagmus (OKN) has been studied in 13 adult cats with unilateral lesions. OKN was induced by rotating the visual field around the animals in both binocular and monocular conditions. (1) No deficits of OKN appeared following unilateral ablations of visual cortex. (2) Lesions of different parts of suprasylvian cortex were made: the posterior and the middle suprasylvian cortex involving area 7 and the lateral suprasylvian area (LSA). Only the middle suprasylvian cortex damage produced on OKN asymmetry due to a decrease of the slow-phase velocity directed toward the side of the lesion. The deficits were compensated for within about 10 days. We conclude that the middle suprasylvian cortex and particularly LSA regulate the ipsilateral slow phases of OKN.

Responses of visual cells in cat superior colliculus to relative pattern movement

Are there visual cells in the cat superior colliculus, selectively sensitive to relative pattern movement? Based on extracellular recordings from paralyzed pretrigeminal preparations, a sample of 76 collicular units could be divided into two main types according to relative movement sensitivity: those that responded optimally and selectively to one specific relative velocity between a small disk and a full-field grating; and those that discharged maximally whenever the grating shifted relative to a disk moving at one specific "absolute" speed, regardless of the precise relative velocity between the two. It was hypothesized that the latter group, in conjunction with extraretinal "calibration" cues, may be part of a neural mechanism encoding spatial depth in terms of motion parallax.

Effects of lateral suprasylvian visual cortex lesions on visual localization, discrimination, and attention in cats

Experiments were carried out to begin to define the behavioral functions of the lateral suprasylvian (LS) visual area of the cat's cortex. Behavioral tasks were chosen for analysis on the basis of previous suggestions in the literature concerning possible functions of LS cortex and its afferent pathways. These tasks included the ability of cats to orient the head and eyes to a stimulus presented in particular locations in the visual field, the ability to learn successive reversals of a two-choice visual pattern discrimination, and the ability to maintain or shift attention between relevant or irrelevant visual form and brightness cues. Eight cats were trained on each of these tasks. Four of the cats then received bilateral lesions of LS cortex, including the AMLS and PMLS regions, and the remaining 4 cats were used to assess normal retention. The LS cortex lesions had no significant effect upon performance of any of the behaviors tested. Thus, this region of cortex appears to play no essential role in simple brightness, form, and pattern discrimination performance, visual reversal learning, maintaining and shifting visual attention, or orienting the head and eyes to stimuli in the visual field. These results are discussed in relation to previous lesion studies involving large regions of the cat's extrastriate cortex and studies in other species. Possible functions of LS cortex, based upon recent electrophysiological studies, are suggested.

Eye movement-related activities in cells of the lateral suprasylvian cortex of the cat

Investigation of eye movement-related activities and photic responsiveness using behaving cats demonstrated distinctive representations of eye movement signals in different areas of the lateral suprasylvian cortex: visual reafference in the medial bank of the middle suprasylvian sulcus and non-visual signals (proprioceptive reafference or efference copy) in the lateral bank.

A physiological analysis of subcortical and commissural projections of areas 17 and 18 of the cat

1. The corticotectal, corticothalamic and commissural projections of areas 17 and 18 of the cat have been examined using electrical stimulation techniques. 2. In both area 17 and area 18, almost all corticotectal neurones are C cells and have binocular receptive fields. Some of these cells respond equally well to both small moving spots and elongated stimuli, while others only respond to stimuli of restricted length (cf. Palmer & Rosenquist, 1974). Both types are highly direction-selective. A third type of corticotectal C cell responds optimally to long edges or bars and shows only weak direction selectivity. Corticotectal cells generally have fast conducting axons and the majority are encountered in lamina V. About 25% of all cells recorded in lamina V can be antidromically activated from the superior colliculus. 3. Striate and parastriate cells efferent to the thalamus can have either S or C type receptive fields. Corticothalamic S cells are the most common type of efferent cell in lamina VI and have more slowly conducting axons than C cells. Efferent S cells are almost always direction-selective and about half have binocular receptive fields. 4. It is suggested that there may be at least three subgroups within the corticothalamic cells: lamina V C cells project to the pulvinare complex (the same cells may also send axons to the superior colliculus), lamina VI C cells project to the perigeniculate nucleus and lamina VI S cells provide the cortical input to neurones within the lateral geniculate nucleus. 5. In contrast to the corticotectal and corticothalamic projections, the receptive fields of cells projecting through the corpus callosum forth a heterogenous group. All major striate and parastriate receptive field classes are efferent to the contralateral cortex. Their receptive field centres are located close to the vertical mid line and most cells respond best to stimuli moving towards the ipsilateral visual hemifield. Efferent neurones are mostly encountered in lamina III, within about 1mm either side of the 17-18 border zone. 6. Cells orthodromically excited after commissural stimulation have mostly C or B type receptive fields. Unlike efferent callosal neurones, orthodromically activated cells are encountered up to 3 mm into area 18 and can have receptive fields located up to 9 degrees from the vertical mid line. 7. The results are discussed with regard to the possible functional significance of each of the corticofugal pathways.

Direct projections from thalamic intralaminar nuclei to extra-striate visual cortex in the cat traced with horseradish peroxidase

Thalamic projections to the visual cortex were investigated using the Horseradish peroxidase tracing technique. Besides confirmation of a distinct origin of thalamic projections to striate and extra-striate visual cortex, afferents of the intralaminar nuclei (ILN) to visual cortex were demonstrated. These projections of ILN were shown to be specific in that they terminate in areas 18, 19 and Clare Bishop but not area 17. The coupling of these intralaminar projections on to the extra-striate visual system is considered with respect ot orientation of gaze.