Irving T. Diamond

Superior Colliculus of the Tree Shrew: A Structural and Functional Subdivision into Superficial and Deep Layers

Superficial lesions of the superior colliculus produced deficits in form discrimination, while deeper lesions produced, in addition, an inability to track objects. These two syndromes were related to an anatomical subdivision: Superficial lesions resulted in anterograde degeneration in the visual thalamus, whereas lesions confined to the deeper layers produced degeneration in the nonvisual thalamus and in brainstem motor areas.

Evolution of the Pulvinar (Part 1 of 2)

Our evidence from both cytoarchitecture and studies of connections suggests that LE GROS CLARK was correct in postulating that the lateral posterior nucleus of primitive mammals is the homologue to the primate pulvinar. It seems evident that during mammalian evolution both this region of the thalamus and its cortical target have grown larger and more complex. Truly intrinsic subdivisions may have appeared not only in the primates but also independently in other mammalian lines of descent, such as the carnivores. One main goal of our laboratory is to ask how functional subdivisions are related to the increasing subdivisions of structure. Our hope is that this line of inquiry might contribute to an understanding of those functions most recently evolved in mammalian evolution.

Organization of the Visual Sector of the Thalamic Reticular Nucleus in Galago

Projections to and from the visual sector of the thalamic reticular nucleus were studied in the prosimian primate genus Galago by anterograde and retrograde transport of WGA‐HRP injected into the dorsal lateral geniculate nucleus (GLd), pulvinar nucleus, and their cortical targets. Contrary to the idea that thalamic connections with the reticular nucleus are not delimited sharply between nuclei associated with the same modality, our results show a distinct laminar segregation of the projections from the GLd and pulvinar nuclei. The GLd is connected reciprocally with the lateral 2/3 of the caudal part of the reticular nucleus, and the striate cortex sends projections to the same lateral tier. Both sets of projections are organized topographically, lines of projection taking the form of slender elongated strips that run from caudo‐dorsal to rostro‐ventral within the nucleus. The pulvinar nucleus, which projects to several areas of the temporal, parietal, and occipital lobes, including the striate cortex, is connected reciprocally with the medial 1/3 of the caudal part of the reticular nucleus. Every injection into the pulvinar nucleus labelled a wide area of the medial tier, with no indication of visuotopic organization. The projections from the middle temporal area, one of the principal targets of the pulvinar nucleus, also terminate only in the medial tier of the visual sector. And we would expect that, in general, a thalamic nucleus and its cortical target would project to the same part of the reticular nucleus. The case of the striate area is an exception but only in the sense that it projects to the pulvinar nucleus as well as GLd. Thus an injection into a single locus in area 17 produces two parallel strips in the visual sector of the reticular nucleus, but both are in the lateral tier. We propose that each strip arises from a separate population of cells with cortical layer VI, one with an allegiance to the GLd and the other to the pulvinar nucleus.

The Organization of Projections from Subdivisions of the Auditory Cortex and Thalamus to the Auditory Sector of the Thalamic Reticular Nucleus in Galago

Anterograde and retrograde transport techniques were used to study the connexions between different subdivisions of the auditory cortex and thalamus with the thalamic reticular nucleus in the prosimian, Galago. In particular, the goal was to determine whether the primary auditory nucleus, GMv, and its cortical target, area I of the auditory cortex (A I), project to a different region of the auditory sector of the reticular nucleus from the secondary auditory nuclei, GMmc and Po and their cortical targets outside A I. The results show that the projections to and from the auditory sector are indeed segregated: injections of wheatgerm agglutinin‐conjugated horseradish peroxidase into either GMmc or Po labelled cells and terminals along the medial, lateral and ventral borders of the auditory sector, forming a U‐shaped pattern. Projections from area II of the auditory cortex produced almost an identical pattern of the terminal labelling in the auditory sector. In contrast, injections into GMv‐labelled cells and terminals in the centre region of the auditory sector, in the ‘interior’ of the U‐shaped region. Projections from A I were distributed to both the U‐shaped border region and the central core of the auditory sector probably because A I received projections from GMmc, Po and GMv. The significance of these results depends on a comparison between the auditory and visual sectors of the reticular nucleus. Both sectors are divided into tiers or subsectors–one related to the primary relay nucleus, i.e. GLd or GMv, and the other related to the secondary relay nuclei, i.e. pulvinar nucleus, GMmc, Po, etc.

Cells of different sizes in the ventral nuclei project to different layers of the somatic cortex in the cat

Abstract Cells in the ventral group of the cats thalamus were labeled after small injections of horseradish peroxidase restricted to one or a few layers of cortical areas 4, 3a, 3b, or 1. Only small cells were labeled after injections of layers I and II. Much larger cells were labeled by injections involving layers III and IV.

Different distributions of large and small retinal ganglion cells in the cat after HRP injections of single layers of the lateral geniculate body and the superior colliculus

Retinal ganglion cells were labeled with HRP after injecting single layers of GL or single strata within the stratum griseum superficiale (SGS). Only small cells were labeled after injecting small cell C layers and upper SGS. Only large cells were labeled after injecting lower SGS. Small and large cells were labeled after injecting medial interlaminar nucleus (MIN) and layers A and A1.

Visual neglect in the tree shrew after interruption of the descending projections of the deep superior colliculus

Abstract Four tree shrews received tegmental lesions aimed at a transection of those fibers from the deep superior colliculus which cross and descend in the predorsal bundle. In two cases the transection appeared complete or nearly so and these animals suffered a profound deficit in attention which resembles “visual neglect” as that term is used in the neurological clinic, as well as the experimental laboratory. In two cases with lesser lesions, the deficit was less severe. While all of the animals showed some defects in tracking, orienting, and following, and while all tended to sit motionless, they all retained the capacity to discriminate patterns and showed other evidence that they had no sensory or motor loss or a defect in emotion, learning, or level of consciousness. It was concluded that neglect is a specific deficit in attention and is the result of transecting efferent descending pathways from the deep layers of superior colliculus. Since the deep superior colliculus receives fibers from the cortex, it was suggested that neglect in man may be caused by some disruption of the deep tectal system which is normally dependent on the cortex.

Unilateral Ablation of the Auditory Cortex in the Cat Impairs Complex Sound Localization

Unilateral ablation of the auditory cortex in the cat results in a profound deficit in attending to stimuli on the side contralateral to the lesion. The deficit is also manifested in an abnormal perception of left-right pulse pairs when the pulse which leads by a few milliseconds is contralateral to the damaged hemisphere.

Medial superior olive and sound localization.

hardly any of the Mycoplasma species hitherto described do in fact strictly meet the requirements that are formulated in paragraph 6, a. It is appreciated, moreover, that self-evident though these requiTements tare in principle, it will prove difficult or even impossible for any single worker or group of workers to satisfy the demands. However, it is hoped that the gradual creation of a network of reference laboratories may help to ameliorate the situation in this respect and steps are being taken toward this end. At any rate, rather than compromising too much with the above requiroments, it would be wise policy to restrain ones taxonomic efforts and to publish any new isolates merely under their catalog designations, thus providing a useful and necessary means of reference until it is possible to provide a reasonably adequate description. Subcommittee on the Taxonomy of Mycoplasmatales: D. G. FF. EDWARD, Chairman Wellcome Research Laboratories, Beckenham, Kent, England E. A. FREUNDT, Secretary University of Aarhus, Aarhus, Denmark R. M. CHANOCK National Institutes of Health, Bethesda, Maryland J. FABRICANT New York State Veterinary College, Cornell University, Ithaca L. HAYFLICK Wistar Institute, Philadelphia, Pennsylvania R. M. LEMCKE Lister Institute of Preventive Medicine, London, England S. RAZIN Hebrew University, Hadassah Medical School, Jerusalem, Israel N. L. SOMERSON Childrens Hospital, Columbus, Ohio RUTH G. WITTLER Walter Reed Army Institute of Research, Washington, D.C.

Visual attention in the tree shrew: an ablation study of the striate and extrastriate visual cortex.

Removal of the striate area in tree shrews results in increased distractibility, which prevents the animals from learning to discriminate form when hue is an irrelevant and distracting cue. Removal of the extrastriate visual cortex results in the reciprocal deficit: an increase in perseveration manifested by an inability to shift attention when irrelevant dimensions are made relevant.