Cortical afferents to behaviorally defined regions of the inferior temporal and parahippocampal gyri as demonstrated by WGA-HRP.

The inferior temporal gyrus in the monkey appears to be unique among the many extrastriate visual cortices in its importance for normal performance of delayed match-to-sample, a visual memory task. However, the anatomical pathway providing visual information to this portion of the temporal lobe remains unclear. In this study, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was injected into the anterior inferior temporal gyrus and heavy projections were found to arise in cytoarchitectural area TF of the parahippocampal gyrus, as well as moderate projections in more posterior portions of inferior temporal gyrus and perirhinal and entorhinal cortices. Subsequently, WGA-HRP was injected into area TF, resulting in retrogradely labeled cells primarily located in the portions of area TF adjacent to the injection and also in the occipitotemporal sulcus including the ventral portion of the prestriate visual area V4. Moderate projections were found to originate from the dorsal region of area V4 in the lunate sulcus, portions of the caudal parietal lobe, the posterior bank of caudal superior temporal sulcus, and area OPT located at the tip of the superior temporal sulcus. The middle temporal gyrus, foveal prestriate cortex, and area TEO, a transitional area between temporal and occipital visual areas, were all free from retrogradely labeled cells. These latter areas are included in the well-established anatomical system that is known to carry visual information from striate cortex through prestriate to eventually reach dorsal portions of inferotemporal cortex which is coincident with the temporal lobe visual area TE. It is suggested here that there is an additional ventral pathway into area TE as well, which includes projections through portions of the prestriate cortex, occipitotemporal sulcus, and parahippocampal gyrus, ultimately reaching the anterior inferior temporal gyrus, an area that may be specialized to hold visual information over brief periods of time.

Retention deficits produced in monkeys with reversible cold lesions in the prestriate cortex.

Cryodes were implanted over the prelunate and fusiform gyri in 4 monkeys. The intention was to block the prestriate projection to the inferotemporal cortex (IT). Cooling this cortex produced deficits that were completely reversed by removing the cold. The deficits appeared in the recall of visual discriminations that were learned prior to the application of the cold, but new discriminations were learned during cooling at the same rate as in control animals. This closely resembles the results of ablation experiments in this same cortex. There was no deficit when cooling this area on a delayed match-to-sample (DMS) task that required the animals to hold visual information over delays of 10 or 45 s. However, performance was close to chance during cooling when the delays were 6 min. With this long delay, when cooling was done separately at sample when the stimulus is received, or at match when the information is recalled, a significant deficit occurred only at match. The results are consistent with the suggestion that this area is involved in retrieval of visual information from long-term memory.

The effects of monocular deprivation on the size of GAD+ neurons in the cat's dorsal lateral geniculate nucleus.

Previous studies have shown that suturing one eyelid closed in a newborn kitten results in profound changes in the development of the visual system. Among these is a retardation in the growth of neurons in the layers of the dorsal lateral geniculate nucleus receiving retinal input from the closed eye. Moreover, the greatest effect appears to be in the largest neurons. The present study examines the effects of monocular deprivation on the perikaryal size of a select group of small lateral geniculate neurons. GABAergic neurons, that may be interneurons. These cells were selectively labeled by an antiserum to glutamic acid decarboxylase (GAD) and immunocytochemical methods. The results demonstrate that GAD+ neurons are among the smallest in the lateral geniculate nucleus and that they are insensitive to the effects of monocular deprivation. That is, GAD+ neurons in deprived laminae A and A1 are similar in size to those in the corresponding, nondeprived laminae. These findings are consistent with the hypothesis that GAD+ neurons are interneurons and therefore not subject to binocular competition in the visual cortex. This interpretation, however, is complicated by additional studies of the postnatal development of GAD+ neurons which reveal that GAD+ neurons grow to their adult size relatively early, before the onset of the critical period. Thus the insensitivity of the perikarya of GAD+ neurons to monocular deprivation may be attributable to their precocious growth.