Subregional and laminar specializations of pyramidal neurons in the macaque anterior cingulate cortex

Abstract

The anterior cingulate cortex (ACC)—a component of both the limbic system and the frontal-executive network—is composed of three anatomically distinct subregions with diverse roles in processing cognitive and emotional information: rostral area 32 (A32), dorsal area 24 (A24), and ventral area 25 (A25). Pyramidal neurons (PYRs) as the neural substrates of cortical communication govern signal processing and integration differently across brain regions, layers and pathways. Their properties and diversity across the heterogenous ACC subregions have yet to be comprehensively characterized in primates. Here, we compared the biophysical and morphological properties of PYRs in layers 2-3 (L2-3) and 5-6 (L5-6) across ACC subregions of young adult rhesus monkeys (8 females, 11 males) using in-vitro whole-cell patch clamp recording with intracellular filling. Results showed the more pronounced laminar differences in biophysical properties of PYRs in A24 and 32 than in A25, that L2-3 PYRs exhibited lower excitability than L5-6 PYRs. Further, A32 contained a higher proportion of cells receiving high-frequency-sEPSC, with L2-3’s enrichment of mushroom spines compared to L5-6. This heterogeneity in laminar differentiation aligns with cytoarchitectural differences across ACC subregions and suggests layer-specific signaling and excitatory drive in A24 and A32. In contrast, A25 showed cellular heterogeneity in firing patterns as well as different inhibitory signaling dynamics from other ACC subregions. Together, these results highlight the heterogeneity in laminar differentiation of PYR properties across ACC subregions, contributing to their diverse circuits and roles in cognitive-emotional integration and disruption in disease. Significance Statement ACC is a heterogeneous region comprising functionally distinct cytoarchitectonic subregions. Our understanding of the heterogeneity of primate ACC has been derived mainly from anatomical data or limited in-vivo electrophysiological studies. This study assessed the properties of pyramidal neurons (PYRs), the fundamental unit of cortical communication, across primates ACC subregions and layers. Our results demonstrate that, although laminar position is a strong determinant of PYR properties across ACC, the magnitude of these laminar differences varies by subregion—from A24 to A25 exhibiting the most to least-pronounced laminar distinctions. These specializations across ACC subregions mirror the gradients in cytoarchitectural, developmental and connectional patterns, and likely support distinct signal processing and network integration underlying cognitive-emotional control through specialized local and long-range circuits.