Reevaluation of the primary motor cortex connections with the thalamus in primates

Abstract

Six injections (approximately 1 mm in diameter) of biotinylated dextran amine (BDA) were placed in different locations of the primary motor cortex of the rhesus monkey. Anterograde and retrograde labeling patterns in the thalamus were charted and individual labeled axons traced in continuous serial sections. Both anterograde and retrograde labeling in the thalamus was extensive, spanning several millimeters mediolaterally and including ventral lateral, ventral anterior, centromedian, and centrolateral nuclei. Paracentral, mediodorsal, lateral posterior, and medial pulvinar nuclei were also labeled. Two basic types of corticothalamic axons were identified: small to medium-width, type 1 axons that formed large terminal fields with small boutons, and thick, type 2 axons that formed small terminal fields with large boutons. Within each group, subtypes were identified based on specific features of the axons and terminals: two subtypes of type 1 axons and four subtypes of type 2 axons. The results revealed multiple modes of corticothalamic connectivity: sparsely distributed type 1 axons, dense plexuses of type 1 axons, type 2 axon terminal fields either singly or in clusters, and mixed plexuses of type 1 and type 2 axons. Only some cells in the plexuses were retrogradely labeled; some plexuses did not contain any labeled neurons, and many retrogradely labeled neurons were in the regions devoid of anterograde labeling. These connectivity patterns differed between thalamic nuclei. The results revealed much more complex relationships between M1 and thalamus than were previously thought to exist. It is suggested that this connectivity is neither of exclusively a feedback nature nor perfectly reciprocal but is subserved by a multitude of channels, most likely originating from different populations of cortical neurons, and feeding into a variety of functionally different neuronal networks, with each processing specific information.

Retrograde analysis of the cerebellar projections to the posteroventral part of the ventral lateral thalamic nucleus in the macaque monkey

“…The complex somatotopographic pattern of selective divergence and convergence in the projections of the DCbN revealed by the present data fits well with the general pattern of organization at many levels of the motor pathway (e.g., Shambes et al, 1978;Anderson and Turner, 1991;Schieber and Hibbard, 1993), including even the pattern of divergence and convergence in the innervation of peripheral motor units by spinal motorneurons (e.g., Sugiuchi et al, 2004). Furthermore, similar to the present findings, other studies have revealed that comingled neurons within particular portions of the motor system project selectively to different targets but are rarely double-labeled (Darian-Smith et al, 1990;Akintunde and Buxton, 1992;Tokuno and Tanji, 1993;Stepniewska et al, 1994;Rouiller et al, 1999;Morel et al, 2005; see also Kultas-Ilinsky et al, 2003). The repeated theme of selective projections within a complex pattern of …”

Glutamic acid decarboxylase isoform 65 immunoreactivity in the motor thalamus of humans and monkeys: γ‐aminobutyric acidergic connections and nuclear delineations

“…However, this statement should be taken as applicable only to the markers analyzed in this study, because physiological and pathway tracing studies imply that certain compartmentalization may exist within VL as well (Asanuma et al, 1983;Mackel et al, 1992;Kultas-Ilinsky et al, 2003).…”

Thalamocortical connections of anterior and posterior parietal cortical areas in New World titi monkeys

“…As noted above, VP receives cutaneous input. The VPs, however, processes inputs from deep receptors of the skin and joints (e.g., Asanuma et al, 1983; e.g., Dykes et al, 1981;Friedman and Jones, 1981;Kaas et al, 1984), and VL is associated with the motor system (Asanuma et al, 1983;Gonzalo-Ruiz and Leichnetz, 1990;Ilinsky and Kultas-Ilinsky, 2002;Kultas-Ilinsky et al, 2003;Stepniewska et al, 1994b;Vitek et al, 1994;Vitek et al, 1996). The anterior pulvinar is a nucleus associated with somatic processing (e.g., Asanuma et al, 1985;Cusick and Gould, 1990; see Grieve et al, 2000 for review;Jones et al, 1979;Pons and Kaas, 1985).…”