Topographic organization in the corticocortical connections of medial agranular cortex in rats

Abstract

Medial agranular cortex (AGm) is a narrow, longitudinally oriented region known to have extensive corticortical connections. The rostral and caudal portions of AGm exhibit functional differences that may involve these connections. Therefore we have examined the rostrocaudal organization of the afferent cortical connections of AGm by using fluorescent tracers, to determine whether there are significant differences between rostral and caudal AGm. Mediolateral patterns have also been examined in order to compare the pattern of corticocortical connections of AGm to those of the laterally adjacent lateral agranular cortex (AGl) and medially adjacent anterior cingulate area (AC). In the rostrocaudal domain, there are notable patterns in the connections of AGm with somatic sensorimotor, visual, and retrosplenial cortex. Rostral AGm receives extensive afferents from the caudal part of somatic sensorimotor area Par I, whereas caudal AGm receives input largely from the hindlimb cortex (area HL). Middle portions of AGm show an intermediate condition, indicating a continuously changing pattern rather than the presence of sharp border zones. The whole of the second somatic sensorimotor area Par II projects to rostral AGm, whereas caudal AGm receives input only from the caudal portion of Par II. Visual cortex projections to AGm originate in areas Oc1, Oc2L and Oc2M. Connections of rostral AGm with visual cortex are noticeably less dense than those of mid and caudal AGm, and are focused in area Oc2L. The granular visual area Oc1 projects almost exclusively to mid and caudal AGm. Retrosplenial cortex has more extensive connections with caudal AGm than with rostral AGm, and the agranular and granular retrosplenial subregions are both involved. Other cortical connections of AGm show little or no apparent rostrocaudal topography. These include afferents from orbital, perirhinal, and entorhinal cortex, all of which are bilateral in origin. In the mediolateral dimension, AGm has more extensive corticocortical connections than either AGl or AC. Of these three neighboring areas, only AGm has connections with the somatic sensorimotor, visual, retrosplenial and orbital cortices. In keeping with its role as primary motor cortex, AGl is predominantly connected with area Par I of somatic sensorimotor cortex, specifically rostral Par I. AGl receives no input from visual or retrosplenial cortex. Anterior cingulate cortex has connections with visual area Oc2 and with retrosplenial cortex, but none with somatic sensorimotor cortex. Orbital cortex projections are sparse to AGl and do not appear to involve AC.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolution of somatosensory and motor cortex in primates

“…As a secondary motor area has been described in rats (Fig. 2) (Neafsey and Sievert, 1982;Reep et al, 1990), further study in tree shrews may reveal additional premotor areas. As in most mammals, the thalamic ventroposterior nucleus projects strongly to both S1 and S2, providing an independent source of activation for both of these areas (Garraghty et al, 1991).…”

Cortico-limbic-striatal circuits subserving different forms of cost-benefit decision making

“…Although the specific contribution that each region makes to this form of decision making remains to be clarified fully, one possibility is that in these situations, increased activity of basolateral amygdala neurons may encode the expected magnitude of reward associated with different choices (Pratt & Mizumori, 1998;Saddoris, Gallagher, & Schoenbaum, 2005;Schoenbaum, Chiba, & Gallagher, 1998). This reward-related information may be relayed to the PFC, which can bias behavior in a particular direction by integrating these signals with other information about the response costs associated with each action, possibly mediated via connections with motor cortices (Reep, Goodwin, & Corwin, 1990;Sesack, Deutch, Roth, & Bunney, 1989). Once a particular course of action has been determined, the transformation of this strategy into the appropriate behavioral output is likely mediated by corticostriatal connections linking the PFC to the NAc.…”

Hippocampal and neocortical interactions during context discrimination: Electrophysiological evidence from the rat

“…Sutherland and Hoesing, 1993;McNaughton et al, 1996) that posterior neocortical regions contribute to the determination of the appropriate cognitive and behavioral strategies to be used by the animal, retrosplenial cortex may serve another key function relevant to context discrimination, and that is to facilitate the appropriate behavioral responses when changes in context are detected. From retrosplenial cortex, updated information may be passed on to striatum (Risold and Swanson, 1995), or to premotor areas of cortex (Reep et al, 1990). An important relay in the latter pathway may include the medial precentral nucleus, or PrCm (also referred to as medial agranular cortex, Reep et al, 1987;Reep and Corwin, 1999).…”

“…The PrCm may play a pivotal role in the implementation of future cognitive strategies (Mizumori et al, 2002;Mizumori et al, under review) for it projects to the striatum (Reep et al, 1987;Reep and Corwin, 1999) as well as to frontal cortical motor regions (Reep et al, 1990). The PrCm-striatal projection could provide spatial context-dependent movement information to the striatum.…”