Correlation between pulvinar-lateralis posterior complex unit activity and eye movements in the cat

Extrinsic and intrinsic connections of the cat's lateral suprasylvian visual area

The lateral suprasylvian visual area (LS) is known to have numerous interconnections with visual cortical areas as well as with subcortical structures implicated in visually-guided behaviors. In contrast, little data is available regarding connections within the LS itself. In order to obtain information about intra-areal connections and to re-investigate LS connectivity with various cortical and subcortical areas, the traces (biocytin or WGA-HRP) was injected into various loci along the medial and lateral banks of the LS. The anterograde tracer, biocytin injections into both medial and lateral bank produced label contained within the respective bank that extended rostrally and caudally from the infection site. In addition, following medical bank injections, considerable label was distributed throughout the fundus and, to a lesser extent, in the lateral bank. In contrast, no label could be detected in the medial bank after lateral bank injections, and, although label was observed in the fundus, it was restricted to the most lateral aspects. Moderate labeling could be observed in the medial bank following the tracer injection into the most rostral aspect of the lateral bank. It is likely that input derived from various visual cortical areas which project to the medial bank of the LS has access to this intra-areal circuitry. This may provide a route by which visual cortical information can be relayed to other cortical and subcortical structures involved in visually-guided behaviors such as the anterior ectosylvian visual cortex, striatum, and the deep layers of the superior colliculus, despite the fact that these structures themselves do not receive substantial direct projections from the visual cortical areas that are associated with the medial bank. Examination of the laminar location of the cells-of-origin of striate and extrastriate projections to LS using retrograde trace, WGA-HRP, revealed that the supragranular laminae of areas 17, 18 and 19 were the source of LS afferents whereas afferents from the other cortical areas (e.g., 20a, 20b, 21a, 21b, 7 and anterior ectosylvian visual area) were from both supra- and infragranular laminae. In addition, all LS subregions received intra-areal afferent projections from all LS cortical laminae. Thus, although rather clear hierarchical relationship between LS and visual cortical areas appears to exist, the interconnections among LS subregions provide no clear evidence of simple hierarchical relationships between regions LS or may have feed-forward and feed-back pathways.

Physiological characterization of pretectal neurons projecting to the lateral posterior-pulvinar complex in the cat

Pretectal neurons projecting to the lateral posterior-pulvinar complex (LP-P) in cats were electrophysiologically identified by their antidromic activation from the LP-P. Their responses to various visual stimuli and to electrical stimulation of the optic chiasm and the lateral geniculate nucleus (LGN) were characterized. In retrograde double-labelling experiments, the pretectal projections to the LP-P and to the LGN were tested for possible overlap. Forty-five neurons were antidromically activated from the LP-P; 55% of them could also be activated orthodromically from the optic chiasm. Most antidromically activated neurons responded to rapid movements of large textured visual stimuli as well as to 'on' or 'off' visual stimulation with short bursts. When stimulated with a slowly moving, large, structured visual stimulus, most cells showed a slight but significant activity increase. None of the neurons projecting to the LP-P was also activated antidromically from the LGN. Thus, the two populations are separate. This is supported by the results from the retrograde double-labelling experiments. None of the LP-P projecting neurons showed any directional selectivity to slow movements of large visual stimuli, a property by which pretectal neurons projecting to the inferior olive are characterized. Thus, neurons projecting to the LP-P do not bifurcate to the inferior olive. Response properties of neurons projecting to the LP-P were very similar to those of the 'jerk' neurons described by Schweigart and Hoffmann (Exp. Brain Res., 91, 273-283, 1992); therefore we believe them to be identical.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical and subcortical afferent connections of a posterior division of feline area 7 (area 7p)

Area 7 of the cat, as identified cytoarchitecturally, includes cortex both on the middle suprasylvian gyrus and on the anterior lateral gyrus. The aim of the experiments reported here was to determine whether within this zone there are subdivisions with qualitatively different patterns of afferent connectivity. Deposits of distinguishable retrograde tracers were placed at 29 sites in and around area 7 of 15 cats; cortical and subcortical telencephalic structures were then scanned for retrograde labeling. Our results indicate that cortex on the anterior lateral gyrus, although often included in area 7, is indistinguishable on connectional grounds from adjacent somesthetic cortex (area 5b). Cortex with strong links to visual, oculomotor, and association areas is confined to the middle suprasylvian gyrus and the adjacent lateral bank of the lateral sulcus. We refer to this discrete, connectionally defined zone as posterior area 7 (area 7p). Area 7p receives input from visual areas 19, 20a, 20b, 21a, 21b, AMLS, ALLS, and PLLS; from frontal oculomotor cortex (areas 6m and 6l); and from cortical association areas (posterior cingulate cortex, the granular insula, the posterior ectosylvian gyrus, and posterior area 35). Thalamic projections to area 7p arise from three specific nuclei (pulvinar; nucleus lateralis intermedius, pars caudalis; nucleus ventralis anterior) and from the intralaminar complex (nuclei centralis lateralis, paracentralis and centralis medialis). Neurons in a division of the claustrum immediately beneath the somatosensory and visual zones project to area 7p. Within area 7p, anterior-posterior regional differentiation is present, as indicated by the spatial ordering of projections from cingulate and frontal cortex, the thalamus, and the claustrum. Area 7p, as delineated by connectional analysis in this study, resembles cortex of the primate inferior parietal lobule both in its location relative to other cortical districts and in its pattern of neural connectivity.