Distinct descending motor cortex pathways and their roles in movement

Abstract

Activity in motor cortex predicts specific movements, seconds before they are initiated. This preparatory activity has been observed in L5 descending 'pyramidal tract' (PT) neurons. A key question is how preparatory activity can be maintained without causing movement, and how preparatory activity is eventually converted to a motor command to trigger appropriate movements. We used single cell transcriptional profiling and axonal reconstructions to identify two types of PT neuron. Both types share projections to multiple targets in the basal ganglia and brainstem. One type projects to thalamic regions that connect back to motor cortex. In a delayed-response task, these neurons produced early preparatory activity that persisted until the movement. The second type projects to motor centers in the medulla and produced late preparatory activity and motor commands. These results indicate that two motor cortex output neurons are specialized for distinct roles in motor control.

Molecular, spatial and projection diversity of neurons in primary motor cortex revealed by in situ single-cell transcriptomics

“…L5 ET 4 located at the lateral side of MOp ( Figure 3b) and was found to be more abundant in the anterior part of MOp whereas in the posterior part, L5 ET 4 mostly resided outside of MOp (Extended Data Figure 3). It has been previously reported that two distinct L5 ET populations in upper and lower layer 5 of the anterior lateral motor cortex (ALM) project to thalamus and medulla, respectively, and played specialized roles in motor control in the ALM 48 .…”

Brain-wide single neuron reconstruction reveals morphological diversity in molecularly defined striatal, thalamic, cortical and claustral neuron types

“…Conventionally this is followed by serial sectioning, imaging of each section, and manual reconstruction of the labeled neurons across many consecutive sections. Although relatively few such studies exist due to the labor-intensive process, they reveal critical features of specific projection neuron types that likely have important functional implications 22,24,[32][33][34][35][36][37][38][39] . The recent development of high-throughput and highresolution fluorescent imaging platforms, such as fMOST 40 and MouseLight 29 , coupled with more efficient sparse viral labeling strategies, now enable the potential for large-scale generation of neuronal morphology datasets.…”

A Head-Fixation System for Continuous Monitoring of Force Generated During Behavior

“…Many studies in modern behavioral neuroscience use head-fixation (Toda et al, 2017;Coddington and Dudman, 2018;Economo et al, 2018). Historically, head-fixed experimental preparations in awake behaving animals have contributed to the study of motor control (Evarts, 1968;Hikosaka and Wurtz, 1983), associative learning (Waelti et al, 2001;Eshel et al, 2015), and even navigation (Dombeck et al, 2010).…”

“…Second, by greatly constraining the behaviors that the animal can perform, it simplifies experimental design and data analysis. For this reason, studies using head-fixation usually focus on the behavior of interest, and the typical measures include licking, EMG measures of arm or mouth muscle activity, bar pressing, and eye movements (Newsome et al, 1989;Schultz et al, 1992;Eshel et al, 2015;Economo et al, 2018).…”