Visuomotor signals for reaching movements in the rostro-dorsal sector of the monkey thalamic reticular nucleus.

TLDR: The data suggest that TRNrd neurons provide motor thalamic nuclei with inhibitory inputs that are predominantly devoid of spatial selectivity, and that these signals modulate how these nuclei engage in both sensory processing and motor output during visually guided reaching behavior.

Abstract: The thalamic reticular nucleus (TRN) collects inputs from the cerebral cortex and thalamus and, in turn, sends inhibitory outputs to the thalamic relay nuclei. This unique connectivity suggests that the TRN plays a pivotal role in regulating information flow through the thalamus. Here, we analyzed the roles of TRN neurons in visually guided reaching movements. We first used retrograde transneuronal labeling with rabies virus, and showed that the rostro-dorsal sector of the TRN (TRNrd) projected disynaptically to the ventral premotor cortex (PMv). In other experiments, we recorded neurons from the TRNrd or PMv while monkeys performed a visuomotor task. We found that neurons in the TRNrd and PMv showed visual-, set-, and movement-related activity modulation. These results indicate that the TRNrd, as well as the PMv, is involved in the reception of visual signals and in the preparation and execution of reaching movements. The fraction of neurons that were non-selective for the location of visual signals or the direction of reaching movements was greater in the TRNrd than in the PMv. Furthermore, the fraction of neurons whose activity increased from the baseline was greater in the TRNrd than in the PMv. The timing of activity modulation of visual-related and movement-related neurons was comparable in TRNrd and PMv neurons. Overall, our data suggest that TRNrd neurons provide motor thalamic nuclei with inhibitory inputs that are predominantly devoid of spatial selectivity, and that these signals modulate how these nuclei engage in both sensory processing and motor output during visually guided reaching behavior. This article is protected by copyright. All rights reserved.

Frequently asked questions

Q1. What are the contributions in "Visuomotor signals for reaching movements in the rostro-dorsal sector of the monkey thalamic reticular nucleus" ?

Here, the authors analyzed the roles of TRN neurons in visually guided reaching movements. The authors first used retrograde transneuronal labeling with rabies virus, and showed that the rostro-dorsal sector of the TRN ( TRNrd ) projected disynaptically to the ventral premotor cortex ( PMv ). In other experiments, the authors recorded neurons from the TRNrd or PMv while monkeys performed a visuomotor task. The authors found that neurons in the TRNrd and PMv showed visual-, set-, and movement-related activity modulation. Furthermore, the fraction of neurons whose activity increased from the baseline was greater in the TRNrd than in the PMv. Overall, their data suggest that TRNrd neurons provide motor thalamic nuclei with inhibitory inputs that are predominantly devoid of spatial selectivity, and that these signals modulate how these nuclei engage in both sensory processing and motor output during visually guided reaching behavior. 

Q2. How did the monkeys perform the VG task?

The monkeys performed the VG task at a success rate of >98%, executing reaching movements promptly after the onset of the GO signal. 

Q3. What is the role of feedback modulation in the movement of monkeys?

The feedback modulation inputs may also contribute to generating spatially non-selective activity or form the background or baseline activity of TRN neurons. 

Q4. How many neurons showed visual- and set-related activity?

Thirteen neurons (14%) showed visual- and set-related activity, 13 (14%) demonstrated visual- and movement-related activities, and 13 (14%) showed set- and movement-related activity. 

Q5. What is the role of the TRNrd and PMv in visual guided movements?

The TRNrd and PMv neurons showed visual-, set-, and movement-related activity modulation, indicating that the TRNrd and PMv are involved in the reception of visual signals and in the preparation for and execution of movement. 

Q6. What is the role of the visual TRN in the attentional processing of sensory signals?

In cross-modal attention involving visual and auditory signals, neurons in the visual TRN showed enhanced activity when monkeys attended to visual signals rather than to auditory signals (McAlonan et al., 2006). 

Q7. How long did the discharge rate of the TRNrd neurons last?

During the 500-ms period before the presentation of the fixation point, the discharge rate of the TRNrd neurons was 40 2 spikes/s (n = 106; mean SEM). 

Q8. What is the population activity of visual-related neurons?

(D) Population activity of visual-related PMv neurons with activity increases (n = 55; blue, right target trials; red, left-target trials) and decreases (n = 20; cyan, right target trials; orange, left-target trials). 

Q9. When did the TRNrd suppress high-baseline discharges?

The authors found that high-baseline discharges were suppressed at several time points, such as after visual cue onset, during preparation for movement, and during execution of movement. 

Q10. How did the authors identify the sector of the TRN that projected to the PMv?

Using the trans-synaptic transport of rabies virus, the authors identified a sector of the TRN that projected to the PMv in a disynaptic manner. 

Q11. What is the role of the TRN in the generation of reaching movements?

This suggests that the TRN sends inhibitory signals to the thalamic relay nuclei to modulate activities at multiple time points in the generation of reaching movements. 

Q12. What was used to verify the recording sites?

The sections for verifying recording sites were mounted on gelatin-coated glass slides, stained with 1% cresyl violet, and then examined by light microscopy (Eclipse 80i, Nikon).