We examine two different descriptions of the behavioral functions of the hippocampal system. One emphasizes spatially organized behaviors, especially those using cognitive maps. The other emphasizes memory, particularly working memory, a short-term memory that requires iexible stimulus-response associations and is highly susceptible to interference. The predictive value of the spatial and memory descriptions were evaluated by testing rats with damage to the hippocampal system in a series of experiments, independently manipulating the spatial and memory characteristics of a behavioral task. No (...) dissociations were found when the spatial characteristics of the stimuli to be remembered were changed; lesions produced a similar deficit in both spatial and nonspatial test procedures, indicating that the hippocampus was similarly involved regardless of the spatial nature of the task. In contrast, a marked dissociation was found when the memory requirements were altered. Rats with lesions were able to perform accurately in tasks that could be solved exclusively on the basis of reference memory. They performed at chance levels and showed no signs of recovery even with extensive postoperative training in tasks that required working memory. In one experiment all the characteristics of the reference memory and working memory procedures were identical except the type of memory required. Consequently, the behavioral dissociation cannot be explained by differences in attention, motivation, response inhibition, or the type of stimuli to be remembered. As a result of these experiments we propose that the hippocampus is selectively involved in behaviors that require working memory, irrespective of the type of material that is to be processed by that memory. (shrink)

Posterior parietal cortex has traditionally been considered to be a sensory association area in which higher-order processing and intermodal integration of incoming sensory information occurs. In this paper, evidence from clinical reports and from lesion and behavioral-electrophysiological experiments using monkeys is reviewed and discussed in relation to the overall functional organization of posterior parietal association cortex, and particularly with respect to a proposed posterior parietal mechanism concerned with the initiation and control of certain classes of eye and limb movements. Preliminary (...) data from studies of the effects of posterior parietal lesions on oculomotor control in monkeys are reported.The behavioral effects of lesions of posterior parietal cortex in monkeys have been found to be similar to those which follow analogous damage of the minor hemisphere in humans, while behavioral-electrophysiological experiments have disclosed classes of neurons in this area which have functional properties closely related to the behavioral acts that are disrupted by lesions of the area. On the basis of current data from these areas of study, it is proposed that the sensory association model of posterior parietal function is inadequate to account for the complexities of the present evidence. Instead, it now appears that many diverse neural mechanisms are locatedin partin parietal cortex, that some of these mechanisms are involved in sensory processing and perceptual functions, but that others participate in motor control, and that still others are involved in attentional, motivational, or emotional processes. It is further proposed that the elementary units of these various neural mechanisms are distributed within posterior parietal cortex according to the columnar hypothesis of Mountcastle. (shrink)

Blindsight is the term commonly used to describe visually guided behaviour elicited by a stimulus falling within the scotoma (blind area) caused by a lesion of the striate cortex. Such is normally held to be unconscious and to be mediated by subcortical pathways involving the superior colliculus. Blindsight is of considerable theoretical importance since it suggests that destriate man is more like destriate monkey than had been previously believed and also because it supports the classical notion of two visual systems. (...) It is also of potential clinical importance, since it has been claimed recently that systematic practice in blindsight can lead to the recovery of normal visual function in patients with cortical lesions. From a review of the literature it is concluded that all of the phenomena of blindsight can be attributed either to light scatter into unimpaired parts of the visual field or to residual vision resulting from spared striate cortex. The possible contribution f other factors is also considered. It is concluded that blindsight studies have generally failed to control for such nonblindsight interpretations partly because of poor methodology and partly because of difficulties in defining the term. (shrink)