Cortical control of oculomotor functions. I. Optokinetic nystagmus

Behind mouse eyes: The function and control of eye movements in mice

The mouse visual system has become the most popular model to study the cellular and circuit mechanisms of sensory processing. However, the importance of eye movements only started to be appreciated recently. Eye movements provide a basis for predictive sensing and deliver insights into various brain functions and dysfunctions. A plethora of knowledge on the central control of eye movements and their role in perception and behaviour arose from work on primates. However, an overview of various eye movements in mice and a comparison to primates is missing. Here, we review the eye movement types described to date in mice and compare them to those observed in primates. We discuss the central neuronal mechanisms for their generation and control. Furthermore, we review the mounting literature on eye movements in mice during head-fixed and freely moving behaviours. Finally, we highlight gaps in our understanding and suggest future directions for research.

Vestibular function in the temporal and parietal cortex: distinct velocity and inertial processing pathways

A number of behavioral and neuroimaging studies have reported converging data in favor of a cortical network for vestibular function, distributed between the temporo-parietal cortex and the prefrontal cortex in the primate. In this review, we focus on the role of the cerebral cortex in visuo-vestibular integration including the motion sensitive temporo-occipital areas i.e., the middle superior temporal area (MST) and the parietal cortex. Indeed, these two neighboring cortical regions, though they both receive combined vestibular and visual information, have distinct implications in vestibular function. In sum, this review of the literature leads to the idea of two separate cortical vestibular sub-systems forming (1) a velocity pathway including MST and direct descending pathways on vestibular nuclei. As it receives well-defined visual and vestibular velocity signals, this pathway is likely involved in heading perception and rapid top-down regulation of eye/head coordination and (2) an inertial processing pathway involving the parietal cortex in connection with the subcortical vestibular nuclei complex responsible for velocity storage integration. This vestibular cortical pathway would be implicated in high-order multimodal integration and cognitive functions, including world space and self-referential processing.

Visual acuity in the short-tailed opossum (Monodelphis domestica)

Monodelphis domestica (short-tailed opossum) is an emerging animal model for studies of neural development due to the extremely immature state of the nervous system at birth and its subsequent rapid growth to adulthood. Yet little is known about its normal sensory discrimination abilities. In the present investigation, visual acuity was determined in this species using the optokinetic test (OPT), which relies on involuntary head tracking of a moving stimulus and can be easily elicited using a rotating visual stimulus of varying spatial frequencies. Using this methodology, we determined that the acuity of Monodelphis is 0.58 cycles per degree (cpd), which is similar to the acuity of rats using the same methodology, and higher than in mice. However, acuity in the short-tailed opossum is lower than in other marsupials. This is in part due to the methodology used to determine acuity, but may also be due to differences in diel patterns, lifestyle and phylogeny. We demonstrate that for the short-tailed opossum, the OPT is a rapid and reliable method of determining a baseline acuity and can be used to study enhanced acuities due to cortical plasticity.

Projections from cingulate cortex to the cat’s thalamic reticular nucleus

The cingulate cortex (CG) and the adjacent region designated as the splenial visual area (SVA) project to areas of the extrageniculate thalamic system that are concerned with processing visual information. En route to the thalamus, they pass through the thalamic reticular nucleus (TRN), an important source of thalamic inhibition. We wished to determine whether SVA axon collaterals projected to the previously defined visual sector of the TRN or a separate projection zone and did this differ from the projection zone of CG. We iontophoretically injected different neuroanatomical tracers into several locations within CG/SVA and traced the labeled axons through the TRN. The CG and SVA have a projection zone that only partially overlaps the dorsorostral regions of the visuocortical projection zone; there was no evidence to suggest separate SVA and CG zones or tiers of label within the TRN. The projection formed only a weak topographic map in the TRN, which is largely defined in the rostrocaudal axis and is similar to that of the area 7 projection; both projections have a high degree of overlap in the dorsal TRN. We postulate that CG/SVA may be involved in the initiation of orientation behaviors via stimulation of thalamic nuclei and attentional mechanisms of the TRN.

Deficits of visual motion perception and optokinetic nystagmus after posterior suprasylvian lesions in the ferret (Mustela putorius furo)

We recently described an area in the ferret posterior suprasylvian (PSS) cortex characterized by a high proportion of direction selective neurons. To answer the question whether area PSS subserves functions similar to cat posteromediolateral suprasylvian area (PMLS) and monkey medial temporal area (MT) we investigated the contribution of area PSS to visual motion perception and optokinetic nystagmus. Ferrets were tested on global motion detection before and after bilateral lesions involving area PSS and control lesions of other extrastriate visual areas. Following PSS lesions motion coherence thresholds were significantly increased both in pigmented and albino ferrets, whereas control lesions sparing PSS did not affect visual motion perception. Optokinetic nystagmus was strongly reduced to absent after PSS lesions. These results indicate that area PSS is crucial for global motion processing in the ferret and in that sense may be functionally equivalent to PMLS in the cat and area MT in the monkey.

Relocation of specific visual functions following damage of mature posterior parietal cortex

Many visual deficits have been reported following damage to specific cerebral sites within posterior parietal cortex. These deficits generally involve aspects of vision including spatial or motion perception and visuomotor control. One characteristic of many of these deficits is that they tend to attenuate over time. Presumably, other cortical regions possess adaptive neuroplastic mechanisms that allow them to accommodate functions that were previously dominated by the damaged region. This report summarizes a series of experiments that examined adaptive cortical plasticity following cerebral cortex damage sustained in maturity. Following bilateral lesions of posterior middle suprasylvian sulcal (pMSs) cortex in the cat, deficits were identified in both visual orienting and landmark discrimination tasks. However, the deficits on the visual orienting task were only profound for the first few days following the lesion and orienting abilities returned to normal levels within the first 2 weeks postlesion. In contrast, no such attenuation of the effect of the lesion was evident on the landmark discrimination task. Following recovery of function on the visual orienting task, individual cortical areas flanking the lesion were bilaterally deactivated with cooling. Reversible deactivation of anterior middle suprasylvian sulcal (aMSs) cortex, but none of the other adjacent cortices, yielded visual orienting deficits that are not found in intact animals during deactivation of aMSs cortex. Therefore, we concluded that the visual orienting functions normally mediated by pMSs cortex were able to relocate to aMSs cortex following lesion of pMSs cortex. Finally, bilateral lesion of both pMSs and aMSs cortices yielded visual orienting deficits that did not attenuate. Overall, this series of experiments demonstrates that certain visual functions may relocate to specific cortical loci following damage to discrete areas within posterior parietal cortex.

Evidence for interacting cortical control of vestibular function and spatial representation in man

The objective of this research was to determine the possible relation between deficits in spatial representation capability and vestibular function following cortical lesions. We thus investigated vestibulo-ocular behaviour in a group of 14 patients with unilateral cortical damage involving the occipito-temporo-parietal junction. Patients were divided in three sub-groups: (1) Group R+: five patients with right sided cortical lesions associated with a left hemi-neglect, (2) Group R-: four patients with right sided cortical lesions with no hemi-neglect and (3) Group L: five patients with left-sided cortical lesions. The patient groups were compared to a group of eight healthy age-matched subjects. The vestibulo-ocular reflex (VOR) was tested in complete darkness by rotating the subject around the vertical axis by sinusoidal rotation at different frequencies, and by steps of acceleration or deceleration. The nystagmus slow phase velocity was measured and plotted as a function of the head velocity and the VOR parameters including gain, bias, time constant and phase were calculated. The cortical lesions induced a significant VOR asymmetry in terms of: a directional preponderance of the VOR gain to the contralesion side, only during sinusoidal rotation, and, in contrast, a VOR bias and a directional preponderance of the VOR time constant and of the nystagmus frequency to the side of the cortical lesion. These latter VOR deficits were the most significant in the R+ group, i.e. in right cortical lesions with hemi-neglect syndrome. These results demonstrate in man, the existence of a cortical influence on vestibular function related to the mechanisms of spatial representation.

Physiological Characterization of Pretectal Neurons Projecting to the Láteral Geniculate Nucleus in the Cat

Single neurons in the pretectal nucleus of the optic tract and posterior pretectal nucleus were extracellularly recorded in anaesthetized cats and tested for antidromic activation after electrical stimulation of the ipsilateral dorsal lateral geniculate nucleus. Cells were further characterized by their response latencies to electrical stimulation of the optic nerve head and the optic chiasm, and by responses to various visual stimuli. 46 out of 188 neurons (24%) were antidromically activated from the lateral geniculate nucleus at response latencies of 0.6 - 2.6 ms. They had low spontaneous activities and preferred fast-moving visual stimuli. 29 of the antidromically activated neurons (63%) could be activated from the optic chiasm with response latencies of 4 - 10 ms. Together with the mean conduction time of 0.8 ms between the optic nerve head and the optic chiasm, this indicates that they receive an indirect retinal input via fast-conducting Y-fibres. Sometimes antidromically activated neurons spontaneously showed irregular burst activity. During unidirectional stimulation with a large moving visual stimulus, burst activity became more regular, and interburst intervals and the duration of single bursts decreased. After the stimulus was stopped, interburst intervals slowly increased until prestimulation activity was restored. The response properties of these neurons could reflect the transfer of saccade-related visual as well as oculomotor signals through the pretectum to the visual thalamus.

Behavioral cartography of visual functions in cat parietal cortex: areal and laminar dissociations

The purpose of this review is to: (1) compare and contrast the relative contributions that the four principle regions in cat extrastriate parietal cortex make to a battery of visual tasks which require motion, spatial, or attentional processing; and (2) examine the laminar parcellation of visual behaviors within one of these parietal regions which mediates multiple visual behaviors. We examined a battery of visual tasks presumed to be mediated by parietal cortex, including direction of motion, differential motion, and landmark discriminations, and visual orienting to moving stimuli. As a control, we also examined performance on form (pattern and object) recognition tasks mediated by the temporal processing stream. The four regions of parietal cortex we examined included the: middle suprasylvian (MS) gyrus (area 7), anterior middle suprasylvian (aMS) sulcus (AMLS, ALLS), posterior middle suprasylvian (pMS) sulcus (PMLS, PLLS), and the dorsal posterior suprasylvian (dPS) gyrus (area 21a). The contributions made to each of the six different behavioral tasks was examined before, during, and after reversible cooling deactivation of each cortical area. Deactivation of pMS sulcal cortex resulted in deficits on all four tasks that required motion, spatial or attentional processing. Deactivation of aMS sulcal cortex resulted in deficits on only tasks that required motion processing. Deactivation of neither aMS nor pMS sulcal cortex yielded any deficits on the form recognition tasks. In contrast, deactivation of dPS cortex only produced deficits on the form recognition tasks. This finding confirmed our early hypothesis that dPS cortex is a key component of the temporal, and not the parietal, processing stream. Regardless of the task, no deficits were identified on any of the six tasks during deactivation of the MS gyrus. We then more closely examined pMS sulcal cortex to determine if its multiple functions could be dissociated on a laminar level. We found that cooling deactivation of the superficial layers (I-III) of pMS sulcal cortex selectively and completely impaired performance on the direction of motion discrimination task, while leaving visual attention unimpaired. Additional deactivation of the deeper layers (IV-VI) resulted in impaired visual attention as assessed with visual orienting. These results show a functional bipartite division of labor between upper and lower cortical layers of pMS sulcal cortex. Therefore, spatial, motion and attentional functions can be localized within visuoparietal cortex on both an areal and laminar level.

Cortical projections from the suprasylvian gyrus to the reticular thalamic nucleus in the cat

The cat's suprasylvian gyrus was injected iontophoretically with either 4% wheat germ agglutinin-horseradish peroxidase, 4% dextran-fluororuby or 4% dextran-biotin. The locations of labelled fibres, presumed terminals and cell bodies were determined with the aid of a camera lucida attachment and computer aided stereometry. Cells from the crown of the suprasylvian gyrus project to the dorsal-most portion of the rostral half of the reticular nucleus. The region or 'sector' is distinct, albeit with some overlap, from the visual sector of the reticular nucleus defined by projections from adjacent extrastriate visual cortices. The projection from the suprasylvian gyrus to the reticular nucleus has a rough topography such that the caudal areas project to the more caudal aspects of the sector and rostral areas project to the more rostral areas of the reticular nucleus. There is a large degree of overlap of rostrocaudal projections from the suprasylvian gyrus within the sector, however, the projections originating from rostral sites are situated in a more ventral location compared to the projection originating from the caudal suprasylvian gyrus. Analysis of the distribution of biotin labelled presumptive terminals did not support the notion of 'slabs' or regional variation in terminal density across the mediolateral thickness of the reticular nucleus. In addition, a number of presumptive terminals were found within the internal capsule which coincided with the position of retrogradely labelled cells in the internal capsule following thalamic injections and appears to be part of the perireticular nucleus. The results suggest that the reticular nucleus may be segregated into sectors connected with modality specific cortical areas (e.g. striate and extrastriate visual areas) and nonspecific sectors connected with polymodal (e.g. area 7) cortical regions. The reticular nucleus and its connections with the suprasylvian gyrus may form an important link in binding eye movements to sensory integrative process through visuomotor and auditory thalamic connections.

Preservation of pointing accuracy toward moving targets after extensive visual cortical ablations in cats

Impairments in reaching toward stationary and moving targets were studied in cats after restricted or extensive removal of visual cortical areas (areas 17, 18 and 19 and lateral suprasylvian visual areas). Regardless of the extent of the cortical lesion, cats were at first unable to localise and reach for a stationary target whereas they were soon able to detect and accurately point toward a mobile one. Moreover, the onset latency of such movements was dramatically increased. During post-operative re-training, the cats were unable to improve their accuracy scores when reaching towards stationary targets. In contrast, full compensation was observed for the accuracy of reaching movements directed toward moving targets. A partial recovery was observed for movement latency values that progressively decreased but left a permanent 30-40 ms impairment following extensive lesions. The role of extrageniculate messages and alternative routes involving other cortical areas in taking in charge the visuomotor activity is discussed.

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)

OKN-related neurons in the rat nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system receive a direct cortical input

It has been previously assumed that the asymmetry of the monocular optokinetic nystagmus (OKN) of lateral-eyed mammals is caused by an absence of visual cortex projections to directional selective neurons in the pretectal nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN). In contrast to this generally accepted hypothesis, we present multiple evidence that OKN-related neurons in the rat NOT-DTN in fact do receive input from the visual cortex. We studied the corticofugal projection to NOT-DTN physiologically, with extracellular single unit recording and electrical stimulation of the optic chiasma and the visual cortex, and anatomically, using retrograde and anterograde tracing techniques. In particular we focussed our attention on the NOT-DTN neurons, which control eye movements during OKN. All OKN-related NOT-DTN cells were activated after optic chiasma stimulation. Forty-five percent of these neurons were also activated after stimulation of the visual cortex (VC). The majority of neurons activated from VC (80%) also responded to monocular stimulation of either eye. On the contrary, most of the neurons that responded to stimulation of the contralateral eye only were not activated from VC. After injection of fluorescent latex microspheres into the NOT-DTN, retrogradely labeled neurons were found in areas 17, 18, and 18A of the visual cortex. Phaseolus vulgaris leucoagglutinin injected into the visual cortex anterogradely labeled fibres and terminals throughout the NOT-DTN complex. Labeled boutons were found in close proximity to OKN-related NOT-DTN cells, selectively stained after horseradish peroxidase (HRP) injections into the inferior olive. Our results demonstrate that NOT-DTN cells in the rat, which are involved in the generation of horizontal OKN, receive a direct input from the ipsilateral visual cortex.

Deficits in speed discrimination following lesions of the lateral suprasylvian cortex in the cat

We examined the role of the lateral suprasylvian (LS) cortex in motion perception by testing the ability of three cats to detect moving targets and to discriminate differences in stimulus direction and speed before and after making bilateral ibotenic acid lesions in LS. The lesions had little or no effect on contrast sensitivity for detecting moving sinusoidal gratings. Moreover, we found no deficits in discriminating opposite directions of motion: the cats discriminated grating directions at threshold contrasts. All three cats, however, showed permanent deficits in discriminating differences in speed and in flicker rate. The deficits were most pronounced at higher temporal and spatial frequencies and at lower contrasts. This result suggests that LS plays an important role in the analysis of stimulus speed. It appears that information needed for discriminating opposite directions of motion may be signalled by visual areas outside LS.

Latent defect in monocular optokinetic nystagmus after neonatal removal of the lateral suprasylvian area in the cat

Three kittens underwent unilateral removal of the lateral suprasylvian area of cortex at the age of 1 month. After normal rearing for two years, their monocular optokinetic nystagmus was studied. During the experiment one eye was 'seeing' the optokinetic stimulus, but the other eye was 'covered'; by implanting scleral coils on both eyes, we measured movements not only in the 'seeing' eye, but also in the 'covered' eye. The stimulus was moved at a velocity between 1 and 40 degrees/s. Additionally, movements of the both eyes were simultaneously recorded in a normal cat. The previous results on movements of both eyes in normal cats which had been derived from the recordings by one coil (Vision Res., 26: 1311-1314, 1986) were confirmed by this experiment and were compared with the results of the lesioned cats. The gains (slow phase velocity/stimulus velocity) of the 'seeing' eye were not significantly different from the normal values. However, the gains of the 'covered' eye were significantly higher than the normal values when the stimulus was presented in the temporonasal direction, at the velocities between 1 and 40 degrees/s to the eye ipsilateral to the lesion and at the velocity of 40 degrees/s to the eye contralateral to the lesion; in the other conditions of stimulation the gains were not significantly different from the normal values.

Cortical control of oculomotor functions. II. Vestibulo-ocular reflex and visual-vestibular interaction

The cortical control of the vestibulo-ocular reflex (VOR) and visual suppression of VOR was studied in 13 adult cats with unilateral lesions. VOR was tested in the dark by sinusoidal rotations of the animal at different frequencies. Visual suppression of VOR was tested in the light by keeping the visual field stationary with respect to the animal. No deficits of VOR and visual suppression of VOR appeared following unilateral ablations of visual cortex. Unilateral lesions of different parts of the suprasylvian cortex were made in the posterior and middle suprasylvian cortex involving area 7 and the lateral suprasylvian area (LSA). After middle suprasylvian cortex damage (particularly area 7), all the animals exhibited a VOR asymmetry due mainly to a gain decrease of slow phases directed towards the side of the lesion. In two animals, transitory spontaneous nystagmus was present in the dark with the fast phase directed toward the side of the lesion. Only when LSA was destroyed, could an asymmetry of the visual suppression of VOR be observed with a loss of the visual suppression during ipsilateral rotations. The VOR deficit was transient: spontaneous nystagmus disappeared within the first postoperative week, the vestibular asymmetry and the loss of visual suppression of VOR were no longer present after 2-3 weeks. We conclude that the middle suprasylvian cortex, particularly area 7, exerts an ipsilateral control on the VOR.