Modular Organization of Signal Transmission in Primate Somatosensory Cortex

Abstract

Axonal patches are known as the major sites of synaptic connections in the cerebral cortex of higher order mammals. However, the functional role of these patches is highly debated. Patches are formed by populations of nearby neurons in a topographic manner and are recognized as the termination fields of long-distance lateral connections within and between cortical areas. In addition, axons form numerous boutons that lie outside the patches, whose function is also unknown. To better understand the functional roles of these two distinct populations of boutons, we compared individual and collective morphological features of axons within and outside the patches of intra-areal, feedforward, and feedback pathways by way of tract tracing in the somatosensory cortex of New World monkeys. We found that, with the exception of tortuosity, which is an invariant property, bouton spacing and axonal convergence properties differ significantly between axons within patch and no-patch domains. Principal component analyses corroborated the clustering of axons according to patch formation without any additional effect by the type of pathway or laminar distribution. Stepwise logistic regression identified convergence and bouton density as the best predictors of patch formation. These findings support that patches are specific sites of axonal convergence that promote the synchronous activity of neuronal populations. On the other hand, no-patch domains could form a neuroanatomical substrate to diversify the responses of cortical neurons.

Thalamocortical interactions shape hierarchical neural variability during stimulus perception

“… 48 , 49 Further, recent anatomical evidence has suggested that both areas show akin amounts of synaptic projected from VPL. 50 Here, we confirmed that during the perceptual detection of the vibrotactile stimulus, the amount of incoming feedforward interactions during the stimulus period is comparable in area 3b and area 1. Additionally, contrary to the hypothesis that propose area 3b as an information relay to area 1, feedforward interactions during stimulation were poorly modulated and mainly sustained by neurons in area 3b with large firing rate variability (hence, with low encoding capacity).…”

Thalamocortical interactions shape hierarchical neural variability during stimulus perception

“…Additionally, areas 3b and 1 were both considered as part of S1, with analogous responses and few or nonclear differences between them (45, 46). Further, recent anatomical evidence has suggested that both areas show akin amounts of synaptic projected from VPL (47). Here, we confirmed that during the perceptual detection of the vibrotactile stimulus, the amount of incoming feedforward interactions during the stimulus period is comparable in area 3b and area 1.…”

“…We dealt with the multiple test problem over delays by using the maximum directed information-theoretic measure over all preselected delays as a test statistic. To assess the significance of this statistic, the original (i.e., non-permuted) estimation was compared with the tail of a distribution obtained by performing 20 equally-spaced (to maximize independent sampling) circular shifts of the target spike train 𝑌 within the range [50,200]ms and computed the corresponding P-value. Hence, the significance test provides three outputs: the significance assessment (0/1), the statistic value and the maximizing delay 𝐷 .…”