Visuomotor control in mice and primates

We conduct a comparative evaluation of the visual systems from the retina to the muscles of the mouse and the macaque monkey noting the differences and similarities between these two species. The topics covered include (1) visual-field overlap, (2) visual spatial resolution, (3) V1 cortical point-image [i.e., V1 tissue dedicated to analyzing a unit receptive field], (4) object versus motion encoding, (5) oculomotor range, (6) eye, head, and body movement coordination, and (7) neocortical and cerebellar function. We also discuss blindsight in rodents and primates which provides insights on how the neocortex mediates conscious vision in these species. This review is timely because the field of visuomotor neurophysiology is expanding beyond the macaque monkey to include the mouse; there is therefore a need for a comparative analysis between these two species on how the brain generates visuomotor responses.

The Visual Cortex in Context

In this article, we review the anatomical inputs and outputs to the mouse primary visual cortex, area V1. Our survey of data from the Allen Institute Mouse Connectivity project indicates that mouse V1 is highly interconnected with both cortical and subcortical brain areas. This pattern of innervation allows for computations that depend on the state of the animal and on behavioral goals, which contrasts with simple feedforward, hierarchical models of visual processing. Thus, to have an accurate description of the function of V1 during mouse behavior, its involvement with the rest of the brain circuitry has to be considered. Finally, it remains an open question whether the primary visual cortex of higher mammals displays the same degree of sensorimotor integration in the early visual system.

Visually guided locomotion and computation of time-to-collision in the mongolian gerbil (Meriones unguiculatus): the effects of frontal and visual cortical lesions

Past research has indicated that many species use the time-to-collision variable but little is known about its neural underpinnings in rodents. In a set of three experiments we set out to replicate and extend the findings of Sun et al. (Sun H-J, Carey DP, Goodale MA. Exp Brain Res 1992;91:171-175) in a visually guided task in Mongolian gerbils, and then investigated the effects of lesions to different cortical areas. We trained Mongolian gerbils to run in the dark toward a target on a computer screen. In some trials the target changed in size as the animal ran toward it in such a way as to produce 'virtual targets' if the animals were using time-to-collision or contact information. In experiment 1 we confirmed that gerbils use time-to-contact information to modulate their speed of running toward a target. In experiment 2 we established that visual cortex lesions attenuate the ability of lesioned animals to use information from the visual target to guide their run, while frontal cortex lesioned animals are not as severely affected. In experiment 3 we found that small radio-frequency lesions, of either area VI or of the lateral extrastriate regions of the visual cortex also affected the use of information from the target to modulate locomotion.

Corticothalamic projections from the primary visual cortex in rats: a single fiber study using biocytin as an anterograde tracer

This study investigates the pattern of axonal projections of single corticothalamic neurons from the rat primary visual cortex. Microiontophoretic injections of biocytin were made in cortical laminae V and VI to label small pools of corticothalamic cells and their intrathalamic axonal projections. After a survival period of 48 h, the animals were perfused and the tissue was processed for biocytin histochemistry. On the basis of the intrathalamic distribution of axonal fields and the types of terminations found in the thalamus, three types of corticothalamic projections were identified. (1) Cells of the upper part of lamina VI projected to the dorsal lateral geniculate nucleus where they arborized in rostrocaudally oriented bands or "rods" parallel to the lines of projection of retinal afferents. (2) Cells of the lower part of lamina VI projected to the lateral part of the lateral posterior nucleus and they also sent collaterals to the dorsal lateral geniculate nucleus where they participated in the formation of rods. (3) The corticothalamic projection of lamina V cells originated from collaterals of corticofugal cells whose main axons reached the tectum and/or the pontine nuclei. These collaterals never terminated within the dorsal lateral geniculate nucleus; they arborized in the lateral posterior, lateral dorsal and ventral lateral geniculate nuclei. All corticothalamic cells from lamina VI displayed the same type of axonal network made of long branches decorated by terminal boutons emitted "en passant" at the tip of fine stalks. Corticothalamic fibers arising from lamina V, however, generated varicose endings in restricted regions of their target nuclei. All corticothalamic axons derived from lamina VI cells, but not those derived from lamina V cells, gave off collaterals as they traversed the thalamic reticular complex. These results demonstrate that corticothalamic fibers arising from the rat primary visual cortex display a lamina-dependent projection pattern. In the light of previous studies on the topographical organization of corticothalamic projections, it is proposed that a similar organizational plan characterizes corticothalamic relationships in other sensory systems in the rat and in other species.

Comparative evidence indicating neural specialization for predatory behaviour in mammals

The evolution of cognitive and sensory specializations must involve concomitant modifications of neural substrates. Ecological correlates of species differences in brain structure are intriguing sources of evidence about such evolutionary specialization but, to date, these have been identified only for gross parameters, such as overall brain size and the size of major brain regions. Here we show that a behavioural specialization in mammals, predation, is associated with species differences in the fine structure of a single neural pathway, the tectospinal tract. Both the relative number of neurons in this pathway and the relative size of their cell bodies were greater in more predatory species than in their less predatory counterparts within each of four separate mammalian orders. Expansion of these analyses to consider comparisons between taxa at a variety of taxonomic levels gave further support to the idea of a relation between predatory habits and the evolution of the tectospinal tract. In addition, within the primates, the number of neurons in the tectospinal tract was significantly correlated with the proportion of prey in the diet. These results therefore appear to provide an example of correlated evolution between a specific neural system and behaviour which applies generally within the mammals. They also help to unify findings from physiological and anatomical studies on a wider range of vertebrate taxa, including reptiles and amphibians.

Some factors affecting pigeons' visual tracking behavior

A novel delayed conditional discrimination procedure was used successfully to investigate some factors affecting pigeons' tracking of visual stimuli. Trials began with the brief illumination of one of the keys (randomly selected) from the left- or right-hand column of a three by three matrix of pecking keys. Then the next key in the same row was briefly lit. Finally, the remaining key in the row was lit along with one (randomly chosen) of the remaining five keys from the left- or right-hand columns. A peck to the former but not the latter key was designated as correct and was rewarded. In Experiment 1 pigeons made correct choices on between 70 and 80 percent of trials, thereby demonstrating an ability to visually track objects. In Experiment 2 tracking accuracy was: a) reduced when either the first or second key in the sequence was omitted, b) improved when the sequence was repeated three times, c) reduced when duration of key illumination was reduced, and d) reduced by delays imposed between keys early but not late in the sequence. It was also found that tracking of vertical and horizontal sequences was approximately equal.

The gerbil: a unique model for research on aging

The Mongolian gerbil (Meriones unguicultatus) is suggested as a model for aging research because of its unique physiological attributes, ease of handling, and because of data previously collected. Factors that demonstrate the gerbils' suitability in fulfulling practical and scientific considerations important in determining a model for aging research are listed. Additionally, several unique physiological attributes of gerbils are described. Based on these attributes and on review of research in gerbils, it is suggested that gerbils can serve as animal models for behavioral and biological processes, and for normative and pathological aspects for aging.

Visually guided head movement in the African chameleon

Visually guided head movement was studied in the African chameleon. Within certain ranges of frequencies and amplitudes, the chameleons followed horizontal, sinusoidal cricket (bait) movement with sinusoidal head movement and no apparent eye movement. Although head movement lagged behind bait movement, the chameleons used head amplitudes that minimized the motion of the bait relative to the head.

L-Dopa and piribedil alter different components of attentional behavior dependent on dose

L-Dopa (3, 10, 30, 100 mg/kg) given SC after carbidopa, and piribedil (10, 30, 100, 300 mg/kg) had biphasic effects on investigation of a novel cup. Gerbils given a low dose of L-Dopa (10 mg/kg) or piribedil (10 or 30 mg/kg) investigated the cup more than did vehicle-injected gerbils, whereas those gerbils given a high dose of L-Dopa (100 mg/kg) or piribedil (300 mg/kg) investigated it less. L-Dopa, but not piribedil, also had biphasic effects on investigation of conspecific odors. The increase in duration with no increase in frequency of investigation suggested an inability to shift attention normally. High-dose attenuation of investigation is considered nonspecific, as many other drugs have the same effect. Locomotor activity scores showed no concomitant increase following low doses, but only a dose-dependent decrease. In addition, L-Dopa (100 mg/kg), but not piribedil at any dose tested, prevented the normal decrement in response to the cup 24 h after injection. As a high response is normally only shown when the stimulus is novel, the data suggest that L-Dopa at the high dose, but not piribedil, interfered with selective attention. Thus, the different dopamine agonists affected different aspects of attention. The data are discussed in relation to neural effects of the drugs as reported in the literature.

Implications for multiple transmitter mediation of amphetamine-induced stereotypies

Gerbils were pretreated with the dopamine (DA) receptor blocker, pimozide, prior to stereotypy-inducing injections of d-amphetamine. Some of the stereotypies induced with amphetamine were blocked, but some were not, supporting the hypothesis that multiple neurotransmitters are involved in the mediation of amphetamine-induced stereotypy. In addition, when apomorphine hydrochloride was injected, different stereotypic motor behaviors were induced than were induced with amphetamine. The behavioral changes following amphetamine treatment could be classified into four groups: (1) those that are probably DA related, based on the fact that they were induced with either amphetamine or apomorphine, and amphetamine induction was blocked with pimozide; (2) those that are probably not DA related because they were not induced by apomorphine, and amphetamine induction was not blocked by pimozide; (3) those behaviors that may be incompatible with stereotypic behaviors, were reduced with either amphetamine or apomorphine, but were not maintained with pimozide; and (4) circling, which was induced with amphetamine, blocked with pimozide, but not induced with apomorphine.

Attention and habituation: catecholamine interactions and sex differences

Norepinephrine (NE)-dopamine (DA) interactions in mediation of long-term habituation were tested using the stimulus-elicited investigation paradigm. Systemic injections of clonidine hydrochloride (CLON), an alpha-adrenergic receptor agonist, given before apomorphine (APO) (1 mg/kg SC), a DA receptor agonist, prevented APO-induced disruption of the duration measure of habituation 25-hr later. A lower dose was effective in female gerbils than that required for male gerbils, suggesting that females are more sensitive to the effects of clonidine. In addition, apomorphine, with or without CLON (0.01 mg/kg), increased locomotor activity in male gerbils but reduced activity in female gerbils. The same dose of CLON that prevented APO-induced disruption of 24-hr habituation did not reverse APO-induced reduction of investigation of an object or an odor, or APO-induced changes in activity. Neither CLON nor desmethylimipramine, a blocker of NE reuptake, had any selective effects on investigation of novel stimuli or short-term habituation showing that relative NE-DA activity can be disrupted without interfering with the behavior, However, CLON interfered with the frequency measure of long-term habituation in male gerbils but not in female gerbils at any dose used (0.0100.3 mg/kg). THe data suggest important sex dependent NE-DA interactions in mediation of long-term habituation.

New methods for analysis of vision in the gerbil

The visual behavior of gerbils has been studied by adapting natural behaviors such as food pursuit, aperture detection, barrier negotiation and ladder climbing. Methods are described for measuring detection and discrimination thresholds using visual orienting tasks. Furthermore, studies of size-distance constancy, anticipation of a moving target's trajectory, and optimal planning of barrier detours show the usefulness of film records for quantitative analysis of complex perceptual abilities. Finally, preliminary studies of gerbils following ablation of primary visual cortex indicate that some visuomotor abilities are cortically dependent.

Toward a neuroethology of mammalian vision: ecology and anatomy of rodent visuomotor behavior

The great diversity of the niches inhabited by rodents, and the variety of the visual demands of these niches, present an excellent prospect for a comprehensive neuroethological analysis of rodent visuomotor behavior. To this end, rodent taxonomy is reviewed, with special attention to the multiple independent invasions of arboreal, terrestrial, fossorial and aquatic niches by distantly related rodent species. Current work on rat, gerbil and hamster is reviewed with emphasis on visual contributions to naturalistic behaviors such as exploration, foraging, predator detection and conspecific recognition.

Organization of the rodent superior colliculus: some comparisons with other mammals

The sensory and motor organization of the superior colliculus has been studied in a variety of mammalian species including rodent, lagomorph, carnivore and primate. Despite differences in the phyletic levels and ecological niches of these species, their colliculi show fundamental organizational similarities. It is suggested that these similarities reflect the retention of an organizational scheme which antedates the radiation of early mammals.

A neuroethological approach to hamster vision

The contributions of the midbrain optic tectum to visuomotor behaviors likely to be important to hamsters in the wild were studied, including aperture detection, insect catching, and barrier avoidance. Following tectal undercuts, hamsters ceased to make direct approaches to apertures in the posterior 180 degrees of the visual field; this appeared to be mediated by a loss of exploratory or scanning head movements. Reorientation to and pursuit of crickets jumping out of grasp into the visual periphery was impaired, though initial approach to them was not. Barrier avoidance was unaffected by tectal undercuts. This pattern is similar to the contribution of the frog and toad optic tectum to analogous visuomotor tasks. The contribution of the tectum to searching and scanning in the hamster is an extension of the basic orienting capabilities dependent on optic tectum in anurans.