Somatic sensory responses in the rostral sector of the posterior group (POm) and in the ventral posterior medial nucleus (VPM) of the rat thalamus

Abstract

The rodent barrel field cortex integrates somatosensory information from two separate thalamic nuclei, the ventral posterior medial nucleus (VPM) and the rostral sector of the posterior complex (POm). This paper compares the sensory responses of POm and VPM cells in urethane-anesthetized rats as a first step in determining how cortex integrates multiple sensory pathways. A complete representation of the contralateral body surface was identified in POm. Trigeminal receptive fields (RFs) of POm and VPM cells were mapped by computer-controlled displacement of individual whiskers; responses were quantified by using peristimulus time histograms. Average RF size was similar in POm (5.1 whiskers) and VPM (4.4 whiskers), but evoked responses in the two nuclei differed significantly according to all other measures. VPM cells were maximally responsive to one single whisker--the "center RF." Stimulating this whisker evoked, on average, a response of 1.4 spikes/stimulus at a latency of 7 ms; surrounding whiskers evoked responses of less than 1 spike/stimulus at latencies of greater than 8 ms. In contrast, POm cells were nearly equally responsive to several whiskers. Quantitative criteria allowed us to designate a single whisker as the "center RF" and stimulating this whisker evoked, on average, a response of 0.5 spikes/stimulus at a latency of 19 ms. VPM cells, but not POm cells, were able to "follow" repeated whisker deflection at greater than 5 Hz. We conclude that, when a single whisker is deflected, VPM activates the related cortical barrel-column at short latency--before the onset of activity in POm. The timing of activation could allow POm cells to modulate the spread of activity between cortical columns.

Developmental and comparative aspects of posterior medial thalamocortical innervation of the barrel cortex in mice and rats

“…Contamination by other fiber systems inadvertently passing through the intrathalamic dye deposits is unlikely. Previous studies have ruled out contamination by certain brainstem afferents (Catalano et al, 1996); contamination by afferents from the zona incerta (Porter and White, 1983; Saper, 1985; Lin et al, 1990) is also unlikely since it lies some distance from our injection target site where POm TCAs to the PMBSF originate (Nothias et al, 1988; Chiaia et al, 1991; Fabri and Burton, 1991; Diamond et al, 1992; Lu and Lin, 1993; Deschenes et al, 1998; Bureau et al, 2006). Contamination by afferents from some of the intralaminar nuclei is possible, but would be negligible because of the sparseness of their innervation (Zhang and Deschenes, 1998).…”

Input-specific effects of acetylcholine on sensory and intracortical evoked responses in the “barrel cortex” in vivo

“…In particular, whisker stimulation May produce frequency-dependent changes at the relay stations along the sensory pathway. In fact, both VPM and Pom tha1amic neurons depress when stimulated above 5 Hz (Ahissar, 2000;Diamond et al, 1992). VPM neurons project primary sensory information to the barrels, whereas Pom neurons project secondary sensory information to the inter-barrel septa (Lu & Lin, 1993).…”

“…In fact, bath VPM and Pom neurons depress when stimulated at frequencies above 5 Hz (Ahissar, 2000;Diamond et al, 1992). Depression ofVPM neurons to repetitive whisker stimulation will have a great impact on cortical sensory suppression because they carry the input producing the primary response in Si.…”

“…• dependent depression found in Pom neurons (Ahissar, 2000;Diamond et al, 1992) could also contribute to cortical sensory suppression, but only for long latency cortical responses because Pom neurons discharge much later than the primary cortical response.…”

Spatiotemporal Characteristics of Neuronal Sensory Integration in the Barrel Cortex of the Rat

“…These investigations have mostly reported a suppressive effect of the stimulation of one whisker on the response to stimulation of another whisker, using both electrophysiological recordings (Brumberg et al 1996;Carvell and Simons 1988;Mirabella et al 2001;Simons 1985;Simons and Carvell 1989) and optical imaging techniques (Goldreich et al 1998;Kleinfeld and Delaney 1996). However, a facilitatory interaction has also been described by several laboratories (Erchova et al 2003;Ghazanfar and Nicolelis 1997;Ghazanfar et al 2000;Shimegi et al 1999Shimegi et al , 2000. These apparently conflicting results could arise from several differences in the experimental protocols used, namely the range of interstimulus intervals (ISIs), the laminar location of the recordings, and the type of recorded neurons.…”