Neural connections of auditory association cortex with the posterior cingulate cortex in the monkey

Clinical studies have indicated that the posterior cingulate cortex is intimately involved in verbal and auditory memory. The present study was performed to obtain anatomical evidence for the above proposal. The connections of the auditory cortical areas with the posterior cingulate cortex in the macaque monkey were examined by retrograde and anterograde tracing methods using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). WGA-HRP was injected into either area TA, TB or TC in the superior temporal auditory cortex. Area TA was reciprocally connected with the posterior cingulate cortex, whereas areas TC and TB were not. The rostral two-thirds of area TA had major connections with the caudomedial lobule in the retrosplenial cortex (CML of Goldman-Rakic et al., 1984) and a minor one with area 23b. The caudal third of area tA was connected only with area 23b. However, neither labeled cells nor terminals were observed in areas 23a, 23c, 29, 30 or 31 in the posterior cingulate cortex following a WGA-HRP injection into the caudal, intermediate or rostral portion of area TA. The present finding suggests that verbal and auditory memory impairment in patients with damage to the posterior cingulate cortex is largely due to damage to the CML and area 23b and not to the other posterior cingulate areas.