THALAMIC AND AMYGDALOID CONNECTIONS OF THE AUDITORY ASSOCIATION CORTEX OF THE SUPERIOR TEMPORAL GYRUS IN RHESUS-MONKEY (MACACA-MULATTA)

Thalamic and amygdaloid connections of three association auditory area s (AA1, AA2, AA3) of the superior temporal gyrus (STG) were investigat ed. In order to define the projections of the particular areas, inject ions of fluorescent tracers were made in three monkeys. Distribution o f labeling indicates that area AA1 differs from areas AA2 and AA3 in p atterns of both thalamo-cortical and amygdalo-cortical connections. Ar ea AA1 receives its predominant inputs from the ventral and dorsal nuc lei of the medial geniculate body (MGB). The amygdaloid projection to the area AA1 originates from the basal nuclei, whereas input from the lateral nucleus was not found. The characteristic thalamic projections to areas AA2 and AA3 originate from the dorsal MGB nucleus and the po lymodal nuclei of the posterior thalamus. The density of projections f rom the dorsal nucleus gradually decreases from area AA1 to area AA3 w hile projections from the Plm, SE and Lim nuclei increase in the same direction. Areas AA2 and AA3 are the source of strong connections with the lateral nucleus of amygdala, which density increases progressivel y when injections shift from area AA2 to AA3. The basal and accessory basal nuclei are the source of a less significant amygdalofugal projec tions to both cortical areas. Thus, our experimental data indicate tha t influence of the polymodal thalamic nuclei increases substantially i n the direction of the higher order association areas. The strong rela tion of the same cortical areas with the lateral amygdaloid nucleus mi ght suggest that areas AA2 and AA3, in addition to auditory input are the site of transfer of complex sensory information to the amygdala.