Differential Gating of Thalamocortical Signals by Reticular Nucleus of Thalamus during Locomotion

Abstract

SUMMARY The thalamic reticular nucleus (RE) provides inhibition to the dorsal thalamus, and forms a crucial interface between thalamo-cortical and cortico-thalamic signals. Whereas there has been significant interest in the role of the RE in organizing thalamo-cortical signaling, information on the activity of the RE in the awake animal is scant. Here we investigated the activity of neurons within the ‘motor’ compartment of the RE in the awake, unrestrained cat during simple locomotion on a flat surface and complex locomotion along a horizontal ladder that required visual control of stepping. The activity of 88% of neurons in this region was modulated during locomotion. Neurons with receptive fields on the shoulder were located dorsally in the nucleus and had regular discharges; during locomotion they had relatively low activity and modest magnitudes of stride-related modulation, and their group activity was distributed over the stride. In contrast, neurons with receptive fields on the wrist/paw were located more ventrally, often discharged sleep-type bursts during locomotion, were very active and profoundly modulated, and their group activity was concentrated in the swing and end of stance. 75% of RE neurons had different activity during the two locomotion tasks. We conclude that during locomotion the RE differentially gates thalamo-cortical signals transmitted during different phases of the stride, in relation to different parts of the limb, and the type of locomotion task.

Interhemispheric Interactions of the Human Thalamic Reticular Nucleus

“…The functional significance of this finding is not clear from this experiment alone but does suggest that the TRN participates in a contralateral inhibitory circuit analogous to that seen arising from layer V of the cortex (Palmer et al, 2012), and the BOLD response recorded here may be driven by cortical-thalamic projections from this very circuit. Such an interpretation is consistent with recent findings in the walking cat (Marlinski et al, 2012), in which profound TRN modulation in the somatosensory sector was observed when the contralateral hemisphere received sensory input during stance. Our data are consistent with such a mechanism in the human brain, and also evidence that this effect can be observed in the passive state.…”

“…Because the resolution limits of our stimulus, the foveal visual field of both the TRN and LGN were not likely mapped with any specificity. This did not produce any obvious omissions in the output of our analysis, as the full extent of the fovea in each LGN was mapped in all participants (Schneider et al, 2004), it is possible that a more accurate retinotopic map of the TRN would be produced with a higher-resolution stimulus, as the visual TRN is known to have receptive fields with spatial acuity Ͻ1°in nonhuman primates (McAlonan et al, 2006). We were also limited in this respect with our ability to perform eccentricity mapping due to our stimulus resolution: future studies may want to supplement these findings with them.…”

“…The TRN is implicated in cross-modal filtering in response to ongoing attention demands (Crabtree and Isaac, 2002;McAlonan et al, 2006). The TRN is proposed to prevent irrelevant incoming sensory information from interrupting an ongoing process.…”

“…These responses modulate the receptive field properties of the thalamus (Cotillon-Williams et al, 2008), a candidate mechanism for attention allocation across the sensory map. The visual TRN responds more vigorously when attending to a visual stimulus within its receptive field in the presence of an auditory distractor than in the opposite situation (McAlonan et al, 2006), and lesions of the TRN abolish any reaction time benefit normally observed with the presentation of a cue/target pair in the contralateral hemifield (Weese et al, 1999).…”

“…It is divided into modality-specific sectors, each respecting the topographic organization of the associated thalamic and cortical regions (Pinault, 2004), and its position in the brain is ideal for synchronizing the activities of disjoint thalamic and cortical processes (Crabtree and Isaac, 2002;McAlonan et al, 2008). It achieves this in part by mediating low-frequency coherence between particular regions (Contreras et al, 1997;Steriade, 1997;Bazhenov et al, 1999;Long et al, 2004).…”