Organization of primate amygdalar–thalamic pathways for emotions

Abstract

Studies on the thalamus have mostly focused on sensory relay nuclei, but the organization of pathways associated with emotions is not well understood. We addressed this issue by testing the hypothesis that the primate amygdala acts, in part, like a sensory structure for the affective import of stimuli and conveys this information to the mediodorsal thalamic nucleus, magnocellular part (MDmc). We found that primate sensory cortices innervate amygdalar sites that project to the MDmc, which projects to the orbitofrontal cortex. As in sensory thalamic systems, large amygdalar terminals innervated excitatory relay and inhibitory neurons in the MDmc that facilitate faithful transmission to the cortex. The amygdala, however, uniquely innervated a few MDmc neurons by surrounding and isolating large segments of their proximal dendrites, as revealed by three-dimensional high-resolution reconstruction. Physiologic studies have shown that large axon terminals are found in pathways issued from motor systems that innervate other brain centers to help distinguish self-initiated from other movements. By analogy, the amygdalar pathway to the MDmc may convey signals forwarded to the orbitofrontal cortex to monitor and update the status of the environment in processes deranged in schizophrenia, resulting in attribution of thoughts and actions to external sources.

Distribution of the Noradrenaline Innervation and Adrenoceptors in the Macaque Monkey Thalamus

“…1981 ; Russchen et al. 1987 ; Timbie et al. 2020 ), and consequently, it is the most “limbic” sector within MD.…”

Serial Prefrontal Pathways Are Positioned to Balance Cognition and Emotion in Primates

“…The number of synapses evident even at very high resolution suggests that A32 has a major impact on A25. The only other system in which we have seen such a high density of labeled synapses at high resolution was in the pathway from the amygdala to the magnocellular mediodorsal thalamic nucleus (Timbie et al, 2020), although the overall patterns were distinct in these diverse pathways.…”

Closing the gap from transcription to the structural connectome enhances the study of connections in the human brain

“…For example, tract-tracers require injections in the living brain, which preclude their study in humans. [19][20][21][22][23][24][25][26] Other tracers such as fluorescent dyes, F I G U R E 1 The integration of diffusion MR tractography with transcriptional and anatomical variation can be used to identify conservation and variation in connectivity patterns in humans relative to other species. Diffusion MR tractography viewed from sagittal, A, B; and coronal slices show fibers (ie, tracts) that course through the white matter.…”