Thalamic projections to S‐I in macaque monkey

Abstract

The organization of thalamic input to functionally characterized zones in primary somatosensory cerebral cortex (S-I) of macaque monkeys (Macaca mulatta) was investigated using the method of labelling by retrograde transport of horseradish peroxidase (HRP). It was found that the cell columns positioned at the posterior margin of the band of cortex representing a given body region receive thalamic input from a posterior level of the ventroposterior thalamic nucleus (VP), and that cell columns at successively more anterior positions within that band receive input from successively more anterior levels of VP. The extreme posterior and anterior margins of the S-I hand, foot and face areas receive input from neuron populations which are not as widely separated in the anteroposterior dimension of VP as the neurons projecting to the extreme anterior and posterior margins of the proximal limb and trunk representations in S-I. These characteristics of the organization of the projections from VP to S-I are consistent with the view that the body representations in VP and S-I have the same connectivity and differential submodality distribution; and with the idea that thalamocortical conncetions only exist between functionally equivalent neuron populations in VP and S-I.

Thalamo‐cortical connections of areas 3a and M1 in marmoset monkeys

“…The cortical connections of area 3a are distinct from other somatosensory areas in that area 3a receives its densest input from cortical areas associated with the motor system, including the primary (M1), supplementary (SMA), and premotor (PM) areas. Area 3a is also densely interconnected with areas in the posterior parietal cortex (Huffman and Krubitzer, 2001), which is associated with complex behaviors such as goal-directed reaching (Ferraina and Bianchi, 1994;Snyder et al, 1997Snyder et al, , 1998Andersen et al, 1997; for reviews, see Mountcastle et al, 1984;Andersen et al, 2000) Although the thalamic connections of other anterior parietal fields have been well investigated (Whitsel et al, 1978;Jones et al, 1979;Nelson and Kaas, 1981;Cusick et al, 1985;Mayner and Kaas, 1986;Cusick and Gould, 1990;Krubitzer and Kaas, 1992; for reviews, see Jones, 1985;Kaas and Pons, 1988), only a few previous studies in monkeys have examined the thalamo-cortical connections of area 3a. Furthermore, most studies define area 3a by using architectonic criteria alone, which can be problematic (Jones and Porter, 1980).…”

On the Question of the Ventral Intermediate Nucleus in Primate Thalamus (Part 2 of 2)

“…According to recent physiological stud ies [44,71] the VBC can be functionally di vided into centrally located 'core' and pe ripherally located 'shell' zones. In ma caque, the core zone contains neurons ac tivated primarily by cutaneous tactile re ceptors [44], receives dense projection from the dorsal column nuclei [10], and contains clusters of spinothalamic pre terminals after cord hemisection [II].…”

“…The 'intermediate zone' also receives input from the vestibular complex in both cat [7,41,63] Several investigations have indicated that the rostral 'shelf zone (i.e., Vim) pro jects to area 3a [24,30,33,66,71]. Physio logical studies have indicated that the cor tical area 10 which Vim projects (i.e., 3a) contains cells which are activated by slow ly adapting muscle and joint receptor in put [16,59,62,71]. Although area 3a has classically been described as the most ros tral part of S-I [71], recent evidence by Jones et al [29] includes the portion of 3a to which the intermediate thalamic zone (VPL0/V1C ) projects as part of the motor cortex: area 4.…”

“…In macaque, the portion of the shell imme diately rostral to the central core corre sponds in location and cytoarchitecture to the area of ventral tier acknowledged as the rostral half of VPL0 [57] or Vim [24, 51], and as sVL in cat [28]. Cells in this re gion respond to input from deep receptors [44,71], including those located in joint and muscle [3,[36][37][38][39]. In both cat [9,28,62] and primate [10,II] cells of this region are relatively large (in comparison to those in VPL), scattered in appearance (as opposed to the cell clusters in VPL) and contain a sparse amount of scattered spin othalamic preterminals (as contrasted with VPL which contains dense medial lemniscai and patchy spinothalamic in put).…”

“…Physio logical studies have indicated that the cor tical area 10 which Vim projects (i.e., 3a) contains cells which are activated by slow ly adapting muscle and joint receptor in put [16,59,62,71]. Although area 3a has classically been described as the most ros tral part of S-I [71], recent evidence by Jones et al [29] includes the portion of 3a to which the intermediate thalamic zone (VPL0/V1C ) projects as part of the motor cortex: area 4. The postcruciate dimple of cat cortex (which corresponds to area 3a of primate) receives not only group 1 mus cle afferent input [3,[36][37][38], but also ves tibular input [42,55].…”