Thalamocortical Connections of Parietal Somatosensory Cortical Fields in Macaque Monkeys are Highly Divergent and Convergent

Abstract

We examined the organization and cortical projections of the somatosensory thalamus using multiunit microelectrode recording techniques in anesthetized monkeys combined with neuroanatomical tracings techniques and architectonic analysis. Different portions of the hand representation in area 3b were injected with different anatomical tracers in the same animal, or matched body part representations in parietal areas 3a, 3b, 1, 2, and areas 2 and 5 were injected with different anatomical tracers in the same animal to directly compare their thalamocortical connections. We found that the somatosensory thalamus is composed of several representations of cutaneous and deep receptors of the contralateral body. These nuclei include the ventral posterior nucleus (VP), the ventral posterior superior nucleus (VPs), the ventral posterior inferior nucleus (VPi), and the ventral lateral nucleus (VLp). Each nucleus projects to several different cortical fields, and each cortical field receives projections from multiple thalamic nuclei. In contrast to other sensory systems, each of these somatosensory cortical fields is uniquely innervated by multiple thalamic nuclei. These data indicate that multiple inputs are processed simultaneously within and across several, ‘hierarchically connected’ cortical fields.

Spatiotemporal trajectories of reactivation of somatosensory cortex by direct and secondary pathways after dorsal column lesions in squirrel monkeys

“…7) had foci for the 3 digits in expected locations for area 3b, but foci for only digits 2 and 3 in area 3a, and digits 1 and 2 in area 1. Additional foci were detected caudomedially in area 2 or perhaps area 5, where more convergence of inputs from digits is expected (Cooke et al, 2014; Padberg et al, 2009; Padberg et al, 2010; Pons et al, 1985). …”

Cell‐poor septa separate representations of digits in the ventroposterior nucleus of the thalamus in monkeys and prosimian galagos

“…Using vibration and flutter stimuli on the hand and 2-deoxyglucose techniques to reveal the locations of increased metabolic activity in VP, Juliano et al (1983) concluded that the digits are represented lateral to that of the face and medial to that of the foot. Studies of thalamocortical connections established that injections in the digit-hand representations of area 3b in macaque labeled dorsoventrally orientated slabs of neurons in the hand subnucleus of VPL, but included little about the representations of individual digits (Jones et al, 1979; Nelson and Kaas, 1981; Darian-Smith et al, 1990; Padberg et al, 2009). Likewise, the limited microelectrode mapping of VP in the recent study of Padberg et al (2009) located representations of digits in VPL just lateral to VPM, but not territories for individual digits.…”

Large-scale functional network overlap is a general property of brain functional organization: Reconciling inconsistent fMRI findings from general-linear-model-based analyses

“…Histological studies report extensive convergent and divergent fiber projections among cortical regions and between cortical and subcortical structures (Boucsein et al, 2011; Cappe et al, 2009; Dancause et al, 2006; Driver and Noesselt, 2008; Padberg et al, 2009; Schnepel et al, 2015; Stepniewska et al, 2015). These data indicate that intermixed neurons in the same cortical regions receive inputs from and send outputs to extensive cortical and subcortical areas.…”