# The role of the cortex and brainstem in motor preparation for proximal and distal upper extremity movements

> **NIH NIH R01** · NORTHWESTERN UNIVERSITY · 2024 · $368,488

## Abstract

Project Summary
During motor preparation, millions of interconnected neurons work together to give rise to a ‘planned’ movement.
We currently know little about the brain circuits and the communication between them in an intact nervous system
during the preparation for shoulder or shoulder and hand combined movements. This gap in basic knowledge
blocks the investigation of motor deficits in pathological conditions, such as hemiparetic stroke and Parkinson’s.
A central movement plan is sent to targeted muscles via descending pathways. In humans, both corticospinal
tracts (CSTs) that largely bypass the brainstem, and cortico-reticulospinal tracts (C-RSTs), via the brainstem,
project to the upper extremity muscles. Although both proximal muscles and distal flexors receive projections
from C-RSTs, distal extensors receive relatively less. Thus, the CSTs remain the primary resource for recruiting
distal extensors. Therefore, we hypothesize that in able-bodied adults, distinct communication among various
cortical areas, as quantified by cortical-cortical-connectivity (CCC), drives the CST and modulates the
brainstem’s excitability to increase or decrease the reliance on the RSTs. This modulation is dependent on motor
pathway connectivity (aim 1) and motor demands (aims 2 and 3). Forty able-bodied adults will be recruited to
participate in the designed experiments in all three aims. In aim 1, participants will self-initiate hand opening
(OPEN) or arm lifting (LIFT) task 5-6 s after a ‘ready’ sound (80dB); or move as quickly as possible after either
a ‘go’ (80dB) or a ‘startling’ (115dB) sound that occurs 1.5-3 s after the ‘ready’ sound. We will quantify the default
CCC for the self-initiated motor tasks, and the startle responses following a ‘startling’ sound compared to a ‘go’
sound. Because the startling sound activates the reticular formation and releases the prepared movements via
RSTs, a short reaction time (< 120ms) will ensure the use of RSTs. Besides, because RSTs branch to multiple
spinal segments, increased muscle co-activation patterns will reflect an increased brainstem activity during motor
preparation. We expect to demonstrate that preparatory CCCs for OPEN and LIFT are different in healthy adults
because shoulder abductors are more strongly innervated by RSTs, and finger extensors are primarily innervated
by CSTs. In aims 2 and 3, participants will perform LIFT (aim 2) or hand opening while arm lifting (OPEN+LIFT,
aim 3) against various shoulder abduction loads. We will demonstrate that CCCs will show motor demand-
induced alterations that either increase or suppress the brainstem’s excitability.
The proposed study will establish the default CCCs prior to OPEN, LIFT, or OPEN+LIFT tasks for the first time.
We will also demonstrate the neuroanatomical connectivity- and task demand-dependent cortical modulation of
the brainstem’s excitability in able-bodied adults. The proposed basic research fits the NINDS's focus for
understanding an intact...

## Key facts

- **NIH application ID:** 10845376
- **Project number:** 5R01NS120226-04
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** JUN YAO
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $368,488
- **Award type:** 5
- **Project period:** 2021-06-01 → 2026-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10845376

## Citation

> US National Institutes of Health, RePORTER application 10845376, The role of the cortex and brainstem in motor preparation for proximal and distal upper extremity movements (5R01NS120226-04). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10845376. Licensed CC0.

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