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P Grobstein

Publications and source records attributed to P Grobstein.

At least 19 recordsLinked to original sources
PubMed1998

The effects of telencephalic lesions on visually mediated prey orienting behavior in the leopard frog (Rana pipiens). II. The effects of limited lesions to the telencephalon.

Unilateral removal of the telencephalon in the leopard frog, Rana pipiens, produces a contralateral deficit in visual prey orienting behavior [Patton and Grobstein, 1997]. In mammals, such deficits are most commonly associated with damage to the isocortex, a pallial derived structure. In contrast, we here report that in leopard frogs, lesions that remove substantial areas of one telencephalic lobe, including virtually the entire pallium, have no discernible effect on visual orienting behavior. Restricted lesions to the ventrocaudal telencephalon, however, produce an effect that closely resembles that produced by the complete removal of one telencephalic lobe. The 'critical area' that is both included in all lesions that are effective in producing a severe deficit and excluded from all ineffective lesions includes a portion of the caudal striatum. The striatum is known to play a significant role in anuran vision. It thus seems likely that the deficit produced by unilateral removal of the telencephalon in the leopard frog is due specifically to the removal of the caudal striatum. Unilateral lesions to the striatum have previously been shown to produce a contralateral deficit in visual orienting behavior in cats, and a role for the striatonigral pathway in the production of the visual orienting deficit that follows visual cortex lesions has been proposed. The current findings call attention to the possible general importance of the striatum in the control of vertebrate visual orienting behaviors.

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PubMed1998

The effects of telencephalic lesions on visually mediated prey orienting behavior in the leopard frog (Rana pipiens). I. The effects of complete removal of one telencephalic lobe, with a comparison to the effects of unilateral tectal lobe lesions.

In this paper, we report studies aimed at characterizing the relationship between forebrain and midbrain systems involved in the control of prey orienting behavior in the leopard frog. In frogs, unilateral forebrain lesions, like unilateral tectal lobe lesions, have their most prominent effects in the contralateral monocular visual field. Such lesions produce partial reductions in response frequency in the binocular visual field as well. Similar sequelae follow unilateral tectal lobe removal. These findings suggest that the effects of unilateral forebrain removal can be largely attributed to removal of a facilitating influence on the tectal lobe on the same side of the brain. In the case of both forebrain and midbrain lesions, behavior was assayed not only in terms of the frequency with which animals responded to stimuli at various locations in the visual field (as is usually done) but also in terms of the latency of whatever responses were observed. A striking inverse relationship between response frequency and response latency was found, both in lesioned and in normal frogs. This relationship has not previously been noticed, doesn't appear to be an obvious consequence of any existing models of the neuronal circuitry underlying anuran orienting behavior, and is difficult to account for in terms of the time scales associated with axonal conduction times and synaptic delays. It may be easier to account for in terms of the responses to perturbation of large interacting systems of neurons, and this possibility seems worthy of further exploration.

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PubMed1990

Tectal connectivity in the frog Rana pipiens: tectotegmental projections and a general analysis of topographic organization.

Recent studies of visually elicited orienting in the frog Rana pipiens suggest that tectofugal signals important in this behavior relay in the midbrain tegmentum before descending to the spinal cord. They also suggest that the high degree of topographic organization displayed by the retinotectal projection may be less characteristic of other tectal afferent and efferent pathways. To explore these possibilities, we have studied patterns of retrograde and anterograde labelling following multiple and single injections of horseradish peroxidase into the tectum. We have found that the midbrain tegmentum is a major terminal zone for tectal efferent projections. Our material also provided a description of the boundaries of other structures which project to and receive input from the tectum. With this background, we studied topographic organization by analyzing for each structure the distribution of labelling following multiple injections, and comparing it with the label distribution following single injections at tectal loci with known visual field input. Multiple injections produced patchy anterograde and retrograde labelling in the nucleus isthmi, with the number of patches corresponding to the number of tectal sites injected. Single injections produced labelling in restricted regions of the nucleus isthmi, the location of which varied systematically with the location of the tectal injection site. In all other structures studied, labelling was more evenly distributed following multiple injections. In none of these structures could we detect systematic variations in the location of labelling associated with variations in the location of single tectal injection sites, and the labelling following single injections was frequently coextensive with that following multiple injections. We also found no evidence that there exist structures which project to or receive input from particular tectal regions and not others. We conclude that there exist adequate neuroanatomical substrates for a tectotegmentospinal pathway believed to be important for visually elicited orienting in the frog. We also conclude that a high degree of topographic organization is more the exception than the rule in considering tectal connections generally in the frog. Topographic organization was readily apparent in connections related to the nucleus isthmi but not in connections related to any other nonretinal structure.

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PubMed1989

The organization of descending tectofugal pathways underlying orienting in the frog, Rana pipiens. I. Lateralization, parcellation, and an intermediate spatial representation.

We have studied the visually triggered orienting behavior of frogs following complete unilateral transection of the neuraxis at the junction of the medulla and spinal cord, as well as after smaller lesions at the same level. Complete transection produces the same behavioral deficit as previously reported (Kostyk and Grobstein 1982, 1987a) for a similar lesion at the junction between midbrain and medulla. Lesioned frogs failed to turn toward stimuli at all locations in the ipsilateral visual hemifield, responding instead with forwardly directed movements in which there was a persistance of variations related to stimulus elevation and distance. Responses to stimuli in the contralateral visual hemifield were normal. Similar deficits were seen after smaller lesions restricted to a medial white tract. Partial damage to the tract resulted in turns of reduced amplitude for stimuli throughout the ipsilateral hemifield. Lesions to adjacent tissue were without effect on the behaviors studied. In all animals, we observed a strong correlation between turn amplitude for lateral stimuli and the distance at which the animals switched from snapping to hopping. These observations provide new evidence that a transformation from a retinocentric to a lateralized and parcellated form of spatial representation occurs in going from the retinotectal projection to the descending tectofugal pathway in the caudal midbrain, and that this form of representation remains stable until the spinal cord. A second transformation involved in determining the actual movement to be triggered must occur subsequently. Our findings also suggest that the signals underlying orienting turns may not descend into the spinal cord on tectospinal axons, and suggest that the lateralization of descending signals probably occurs coincidentally with a synaptic relay in the midbrain tegmentum.

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PubMed1989

The organization of descending tectofugal pathways underlying orienting in the frog, Rana pipiens. II. Evidence for the involvement of a tecto-tegmento-spinal pathway.

In the frog, identical orienting deficits, involving a failure to turn toward stimuli in the ipsilateral hemifield, can be produced by small white matter lesions either in the caudal mesencephalon (Kostyk and Grobstein, 1987a) or in the caudal medulla (Masino and Grobstein, 1989). These findings suggest that descending turn signals may run uninterrupted from the midbrain to the spinal cord, and that something other than tectospinal axons may carry such signals. We here report studies to determine whether there is a tecto-recipient structure whose axons pass through the known critical lesion sites in the caudal mesencephalon and medulla, and whether damage to such a structure, sparing tectospinal pathways, produces an orienting deficit. Horseradish peroxidase (HRP) was applied to behaviorally effective lesions in the caudal medulla and the resulting labelling patterns compared with those resulting from application of HRP to nearby but behaviorally ineffective lesions at the same rostrocaudal level. A column of large cells in the ventrolateral midbrain tegmentum (including nMLF as well as parts of AV and PV) was robustly labelled in all effective lesion cases, and less frequently labelled in ineffective cases. A quantitative analysis showed labelling in this region to be more highly correlated with the existence of a behavioral deficit than that in any other brain region. Reconstructions of single retrogradely labelled cells in the rostral part of the column (nMLF) showed that they have dendrites in a position to receive tectal input and axons which pass through the critical lesion sites in both the caudal mesencephalon and the caudal medulla. Tegmental lesions, sparing the tectospinal tracts, produced ipsilateral turning deficits in cases where the large cell column was completely removed but did not when the column was spared. The findings support the hypothesis that tectofugal signals involved in orienting turns descend uninterrupted to the spinal cord on something other than tectospinal axons, and suggest that the critical projections derive from the large cell column of the ventral tegmentum.

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PubMed1988

From the head to the heart: some thoughts on similarities between brain function and morphogenesis, and on their significance for research methodology and biological theory.

A broad review of the phenomena of morphogenesis and of brain function, and of the history of research in these two areas, suggests that there are quite striking similarities between the two sets of biological phenomena. Among other things, both reflect the interaction of internally complex components at several levels of organization, display variance as an essential characteristic, and incorporate information from the environment. It is argued that reductionist approaches are inadequate to deal with fundamental problems of either morphogenesis or brain function, and alternative foundations for research strategy and tactics are discussed. Attention is also given to the question of why morphogenesis and brain function are so similar, and it is suggested that this may reflect the existence of rules of information acquisition, transmission, and storage to which both are subject. Variance, it is argued, is an essential component of information acquisition processes, and hence of biological integrity, at all levels of organization.

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PubMed1988

Between the retinotectal projection and directed movement: topography of a sensorimotor interface.

This article reviews some recent findings on the character of the neuronal organization lying between the optic tectum and motor pattern-generating circuitry in the case of orienting behaviors. It focuses on frogs but notes parallels to existing work on saccade control in mammals and suggests some additional ones for further exploration. In general, the map-like function of orienting does not appear to be subserved by a comparable map-like organization. It is argued that the current conceptual vocabulary for describing interface organization (sensory map, motor map, pattern-generating circuitry) is inadequate and that some additional concepts (activity-gated divergence, intermediate spatial representation) are necessary. Finally, some questions are raised about the appropriateness of the term 'motor map'.

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PubMed1987

Neuronal organization underlying visually elicited prey orienting in the frog--I. Effects of various unilateral lesions.

We have studied the effects on frog orienting behavior of three lesions: unilateral optic nerve section, unilateral tectal lobe ablation, and unilateral transverse hemisection of the neuraxis at a level just caudal to the optic tectum. Unilateral optic nerve section and unilateral tectal lobe ablation produce very similar deficits in visually elicited responses to prey items, an absence of responses for stimuli at locations within the monocular field of one eye. Unilateral hemisection, in contrast, results in abnormalities in visually elicited responses over a wider area, encompassing the entire ipsilateral visual hemifield. The hemisection deficit also differs in character from that following optic nerve section or tectal lesion. Within the affected hemifield, frogs do not fail to respond to stimuli but rather respond with abnormally directed movements. The movements, regardless of stimulus eccentricity on the horizontal, are always forwardly directed. While not varying with horizontal eccentricity, the movements do vary with stimulus elevation and distance. The variation with stimulus distance in the affected hemifield is somewhat different from that in the opposite hemifield. We conclude from the behavior that remains after hemisection lesions that there must exist bilateral descending tectofugal paths capable of triggering movements which vary with stimulus elevation and distance, and a crossed descending tectofugal path capable of triggering turns into one visual hemifield. That the deficit area is larger following a hemisection than following tectal lobe ablation indicates that the hemisection has affected the ability of both tectal lobes to trigger turns in one direction. A possible interpretation of this finding is that the lesion has interrupted not only the crossed descending tectofugal path from one tectal lobe but an uncrossed descending tectofugal path from the other. This hypothetical pathway as well as the others mentioned is incorporated in a model of the organization of the post-tectal circuitry involved in orienting.

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PubMed1987

Neuronal organization underlying visually elicited prey orienting in the frog--II. Anatomical studies on the laterality of central projections.

A complete transverse hemisection of the neuraxis just caudal to the optic tectum in the frog, Rana pipiens, results in a failure to orient toward stimuli in one visual hemifield [Kostyk and Grobstein (1986) Neuroscience 21, 41-55]. The extent of the deficit area implies disturbances in the outputs triggered by both tectal lobes. In this paper we report studies aimed at determining more precisely what damage is involved in producing the hemisection deficit, with the broader objective of identifying particular neural structures which may be important in visually elicited orienting. Small lesions at the level of the hemisection which are restricted to the ventromedial white tracts result in an orienting deficit identical to that produced by a complete hemisection. Large lesions which spare the ventromedial white tracts are without significant effect on orienting turns. The finding is consistent with the hypothesis that the hemisection deficit results from interruption of tectal outflow paths. Interestingly, partial damage of the ventromedial white tracts does not result in disconnection of any local tectal region from premotor circuitry but instead systematically alters the turns triggered from all tectal regions. Ventrolateral lesions at the same level do not produce deficits in orienting but do disturb optokinetic behavior. Introduction of horseradish peroxidase into ventromedial lesions produces retrograde labeling in a large number of structures both rostral and caudal of the lesion. Labeling patterns following introduction of horseradish peroxidase into ventrolateral lesions, which do not affect orienting turns, were qualitatively similar but differed quantitatively. The observed patterns of tectal cell labeling make it unlikely that the hemisection deficit can be accounted for in terms of interruption of direct projections deriving from complementary regions of the two tectal lobes. They also indicate that if there exists an uncrossed tectal outflow adequate to trigger orienting turns, it must be by way of an indirect projection. A more general analysis of the labeling patterns suggests that a crossed tectal projection and uncrossed projections from three midbrain tegmental nuclei (the anterodorsal tegmental nucleus, the nucleus profunds lateralis and the nucleus of the medial longitudinal fasciculus) are likely to be involved in triggering orienting turns. The three midbrain tegmental nuclei are of particular interest in that they provide possible anatomical substrates for an indirect uncrossed descending tectal outflow path.

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PubMed1987

Neuronal organization underlying visually elicited prey orienting in the frog--III. Evidence for the existence of an uncrossed descending tectofugal pathway.

A complete transverse hemisection of the neuraxis just caudal to the optic tectum in the frog, Rana pipiens, results in a failure to orient toward stimuli in one visual hemifield [Kostyk and Grobstein (1986) Neuroscience 21, 41-55]. This finding indicates that each tectal lobe gives rise to a crossed descending pathway adequate to cause turns in a direction contralateral to that tectal lobe, and suggests that each may also give rise to an uncrossed descending pathway adequate to cause turns in the ipsilateral direction. To determine whether there is in fact such an uncrossed pathway, we have studied the orienting behavior of frogs after lesions which interrupt crossed pathways. Two groups of animals were studied. In one group we made midline lesions of the ansulate commissure, through which run the major crossed descending projections from both tectal lobes. In the other group, we combined a complete transverse hemisection with removal of the tectal lobe on the same side of the brain, leaving intact only an uncrossed pathway from one tectal lobe. A persistence of orienting turns was observed in both groups of animals. In both, the direction of the turns was that expected on the assumption that an uncrossed pathway would cause ipsilateral turns. We conclude that such a pathway exists. While both groups of animals turned in the expected directions, they did so for stimuli at unexpected locations. Increasingly eccentric stimulus locations to one side of the mid-sagittal plane were associated with increasing amplitude turns to the other. The observation suggests that tectal regions mapping areas of visual space to one side of the mid-sagittal plane are capable of triggering turns not only in that direction but in the opposite direction as well. In the case of ansulate commissure section, mirrored orienting responses were observed for tactile stimuli as well. These and other behavioral anomalies described in the preceding papers [Kostyk and Grobstein (1986) Neuroscience 21, 41-55 and 57-82] suggest that between the topographic retinotectal projection and the premotor circuitry for orienting there may exist an intermediate processing step, one in which stimulus location is represented in a generalized spatial coordinate frame.

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PubMed1985

Regulation of neuron numbers in Xenopus laevis: effects of hormonal manipulation altering size at metamorphosis.

Xenopus laevis tadpoles reared in a 0.01% solution of 6-n-propyl-2-thiouracil (PTU) are blocked in their development at larval stage 54 but continue to increase in size. When released from the effects of PTU they metamorphose into frogs of sizes significantly larger than those of their untreated siblings. Using this size difference to examine the hypothesis that neuron numbers are matched to the size of their postsynaptic targets during neuronal cell death, we measured the following on stage 66 frogs metamorphosing from PTU-treated and untreated tadpoles: lumbar lateral motor column (L-LMC) motoneuron number and mean nuclear cross-sectional area; thoracic and lumbar dorsal root ganglion (DRG) cell number and mean nuclear cross-sectional area; and muscle fiber number in two representative thigh muscles. A few measurements of neuron number and cell size were also made on untreated and PTU-treated stage 54 tadpoles. The most striking correlations observed were not between peripheral size and neuron numbers but between peripheral size and neuron size. Motoneuron numbers were not increased in the PTU-treated animals, perhaps because the increase in peripheral size involved an increase in muscle fiber diameter rather than an increase in muscle fiber number. Thoracic DRG cell number, but not the sum of thoracic and lumbar DRG cell numbers, was increased. In general, our findings do not support the hypothesis that neuron numbers are matched to peripheral size by a process regulating the amount of cell death that occurs during metamorphic stages in Xenopus laevis.

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PubMed1985

Development of the ipsilateral retinothalamic projection in the frog Xenopus laevis. I. Retinal distribution of ipsilaterally projecting cells in normal and experimentally manipulated frogs.

The distribution of ipsilaterally and contralaterally projecting cells within the retina in Xenopus laevis was studied by injection of horseradish peroxidase into the thalamus on one side of the brain and subsequent determination of the locations of retrogradely labeled cells in both retinas. In normal animals, contralaterally projecting cells were found throughout the retina. Ipsilaterally projecting cells, in contrast, were most frequent in temporoventral retina and largely absent from dorsonasal retina as well as from a region surrounding the nerve head. A similarly restricted distribution of ipsilaterally projecting cells was observed in retinas of animals after regeneration of one optic nerve as well as in animals from which one eye was removed prior to the time when the ipsilateral projection first develops. The restricted distribution of ipsilaterally projecting cells in normal animals raises the possibility that these cells may be produced relatively late in development. This hypothesis is explored in the following paper (Hoskins, S.G., and P. Grobstein (1985) J. Neurosci. 5: 920-929). The fact that similar distributions were seen in normal and experimental animals implies that organization of the ipsilateral retinothalamic projection in X. laevis is not critically dependent either on particular patterns of axonal organization which may be present during normal development or on interactions among fibers from the two eyes.

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PubMed1985

Development of the ipsilateral retinothalamic projection in the frog Xenopus laevis. II. Ingrowth of optic nerve fibers and production of ipsilaterally projecting retinal ganglion cells.

We have studied the development of the ipsilateral retinothalamic projection in the frog Xenopus laevis by analyzing patterns of histochemical reaction product resulting from anterograde transport of horseradish peroxidase (HRP) applied to cut optic nerves in animals of various ages. We have also determined the stages during which ipsilaterally projecting ganglion cells are born using a combination of [3H] thymidine autoradiography and retrograde marking of ganglion cells following injection of HRP into the thalamus. Projections to ipsilateral thalamic terminal zones were first detectable beginning at about larval stage 54. There was a clear asynchrony in innervation, with projections to some terminal zones appearing before projections to others; projections to all terminal zones were present by late metamorphic stages. Within individual terminal zones there were progressive increases in the density of the projections as well as changes in their distribution. By these criteria, development of the ipsilateral projection was not complete at the end of metamorphosis but continued for some months thereafter. Our birth dating studies show that ipsilaterally projecting cells are produced relatively late in development and that, like the development of the projection, the production of ipsilaterally projecting ganglion cells continues postmetamorphically. The vast majority of ipsilaterally projecting cells are born over a period beginning at stage 54/55, when the projection first appears. This stage is significant, since it is at approximately this time that thyroxine-dependent metamorphic events begin. In the following paper (Hoskins, S.G., and P. Grobstein (1985) J. Neurosci. 5: 930-940) we report studies on the involvement of thyroxine in the development of the ipsilateral retinothalamic projection.

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PubMed1985

Development of the ipsilateral retinothalamic projection in the frog Xenopus laevis. III. The role of thyroxine.

The ipsilateral retinothalamic projection in Xenopus laevis normally first appears at about stage 54, at a time when a number of other changes known to be dependent on a rise in circulating levels of thyroxine begin to occur. We have investigated the role of thyroxine in the development of the ipsilateral retinothalamic projection by studying retinal projections and patterns of retinal histogenesis in tadpoles whose ability to produce thyroxine was blocked by treatment with propylthiouracil (PTU), and in similar tadpoles in which thyroxine was restored by injection of small amounts of thyroxine into one eye. PTU-reared tadpoles continue to grow and to add neurons to the retina in a symmetric pattern like that of normal tadpoles at early developmental stages. The PTU-reared tadpoles remained by external criteria at stage 54. Like normal stage 54 tadpoles, the PTU-reared tadpoles either lacked an ipsilateral projection entirely or had an extremely sparse projection. Injection of thyroxine into one eye of PTU-reared tadpoles resulted in the production of substantial ipsilateral projections from the treated eyes as well as shifts to the asymmetric pattern of retinal cell addition which normally begins after stage 54. Such changes were much more prominent in hormone-treated than in untreated eyes, suggesting that they are caused by local action of thyroxine on the treated eyes. With low doses, thyroxine-induced effects on the development of the ipsilateral projection and on retinal histogenesis were restricted to the treated eye. These results suggest that the presence of thyroxine in one eye alone is sufficient to cause the development of the ipsilateral projection.

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PubMed1984

Recovery of the ipsilateral oculotectal projection following nerve crush in the frog: evidence that retinal afferents make synapses at abnormal tectal locations.

The ipsilateral oculotectal projection in the frog is a topographic mapping of the binocular part of the visual field of one eye on the ipsilateral tectal lobe. The underlying neuronal circuitry consists of the topographic, crossed retinotectal projection and an intertectal pathway which relays information from a given point in one tectal lobe to the visually corresponding point in the other. During optic nerve regeneration, there is a period when the terminals of retinotectal afferents are found at abnormal locations in the opposite tectal lobe. Whether they form functional synapses at this time is not known. If so, one would expect to observe correlated abnormalities in the ipsilateral oculotectal projection. To determine whether such abnormalities exist, we have made parallel electrophysiological studies of the recovery of the retinotectal and ipsilateral oculotectal projections following crush of one optic nerve. The earliest stage of recovery was characterized by a lack of significant topographic order in the retinotectal projection and by the absence of a physiologically observable ipsilateral projection. Within a short time, the retinotectal projection became topographically organized and a similarly organized ipsilateral projection appeared. While topographic, the retinotectal projection at intermediate times was abnormal in that the multiunit receptive fields recorded at individual tectal loci were greatly enlarged. Multiunit receptive fields were similarly enlarged in the ipsilateral projection. In addition, some ipsilateral fields included areas of visual space not normally represented in the projection. The abnormalities in both projections subsequently disappeared over the same time course. Throughout recovery there was a high correlation between multiunit receptive field sizes in the contralateral tectal lobe and those at visually corresponding points in the ipsilateral tectal lobe. Enlarged multiunit receptive fields in the contralateral tectal lobe could not be accounted for in terms of optical or retinal abnormalities since single unit receptive field sizes were normal. Nor could they be accounted for in terms of changes in recording characteristics since simultaneously recorded fields activated by the undisturbed eye were normally sized. We conclude that the enlarged fields in the contralateral tectal lobe indicate the presence at individual tectal loci of afferents from wider than normal retinal regions. Similar considerations ruled out optical, retinal, and recording abnormalities as the explanation for the enlarged multiunit receptive fields in the ipsilateral tectal lobe.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1983

Postmetamorphic changes in the lumbar lateral motor column in relation to muscle growth in the toad, Bufo americanus.

Motoneuron number and size (nuclear cross-sectional area) were measured from serially sectioned spinal cords of Bufo americanus to investigate the relation between changes in the lumbar lateral motor column (L-LMC) and postmetamorphic increases in hindlimb muscle fiber number. Previous studies of neuron number in a variety of anuran species reported a correlation between number and body size, suggesting the possible addition of neurons during growth. Our results show a poor correlation between motoneuron number and body size with at most a 25% increase in neuron number occurring over the body size range where previous work had shown a hindlimb muscle fiber increase of ten to 20-fold. Thus, most new muscle fibers must be incorporated into motor units that exist at metamorphosis. Motoneurons, but not ependymal cells, showed a significant size increase with increasing body size; this is perhaps related to an increased motor unit size that results from axonal sprouting. The range of variation of L-LMC cell numbers in newly metamorphosed toads was nearly equal to that of all other toads examined. This suggests that the weak correlations between motoneuron number and size observed in this and previous studies may be due to differential survival of individuals with larger neuron populations rather than to postmetamorphic addition of motoneurons. Our findings also show a strong bilateral correlation of motoneuron numbers, a finding suggesting that factors other than peripheral size may be important in regulating motoneuron number.

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PubMed1982

Visual orienting deficits in frogs with various unilateral lesions.

We have studied the visual prey acquisition behavior of frogs with unilateral optic nerve section, unilateral tectal lobe ablation, and unilateral transverse hemisection at a level between the tectum and the cerebellum. The first two groups of animals oriented normally to stimuli throughout the region of visual field overlap and failed to respond to more peripheral stimuli on one side. Hemisected animals responded to stimuli at all positions in the visual field. For stimuli located contralateral to the lesion, the frogs oriented normally. For ipsilateral stimuli, the frogs oriented forward.

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