Topographic organization of cortical inputs to the lateral nucleus of the macaque monkey amygdala: A retrograde tracing study

The objective of this study was to identify cortical areas that project to the lateral nucleus of the macaque monkey amygdaloid complex. Discrete injections of the fluorescent retrograde tracers Fast blue and Diamidino yellow were placed into different locations within the lateral nucleus. Retrogradely labeled cells were mapped using a computer-aided digitizing system. In the frontal cortex, low numbers of retrogradely labeled cells were observed in medial and orbitofrontal regions (areas 10, 11, 12, 13, 13a, and 14). In the anterior cingulate cortex, low to moderate numbers of retrogradely labeled cells were located in areas 25, 24, and 32. In the insula, there were moderate to high numbers of retrogradely labeled cells in agranular and dysgranular regions. The parainsula cortex also demonstrated a moderate to high number of retrogradely labeled cells. In the temporal lobe, retrogradely labeled cells were most numerous in the rostral (polar) portion of the perirhinal cortex. Large numbers of labeled cells were also located throughout more caudal portions of the perirhinal regions as well as in the entorhinal cortex, area TE, and the superior temporal gyrus. Fewer retrogradely labeled cells were observed in the cortex along the dorsal bank of the superior temporal sulcus, in the parahippocampal cortex, and in area TEO. Although retrograde tracers can provide only limited evidence for topography, we nonetheless noted that the density of retrogradely labeled cells in a cortical area reliably depended on the location of the tracer injection in the lateral nucleus.