# The Human Motor Output Map

> **NIH NIH R01** · NORTHWESTERN UNIVERSITY · 2020 · $414,500

## Abstract

PROJECT SUMMARY/ABSTRACT
All motor output is generated by motoneurons and consequently their firing patterns contain detailed
information about the structure of motor commands. Remarkably, this information is accessible in humans,
because motoneuron spikes are 1 to 1 with those of their muscle fibers. Our overall concept is that
motoneuronal firing patterns vary systematically across the muscles of the human body and that this variation
reflects fundamental connections between the synaptic organization of motor commands, the structure of the
musculoskeletal system and the diversity of motor tasks. To understand these connections, our overall goal is
to create a detailed “motor output map” of the human body, using newly developed array electrodes. The array
electrodes are placed on the skin and are capable of measuring the firing patterns of up to 30 motor units
simultaneously in the underlying muscle. We plan further technical development of these arrays to expand the
range of motor tasks they can be used for. The human motor output map will be created from the analysis of
firing patterns of populations of motor units in muscles throughout the body for matched motor tasks. We will
interpret the resulting map in light of our recent advances in understanding of how firing patterns of
motoneurons are determined by the organization of their synaptic inputs. The effects of excitatory and
inhibitory inputs on firing patterns are fundamental for generating firing patterns, but neuromodulatory inputs
from the brainstem are equally if not more important. These neuromodulatory inputs release serotonin and
norepinephrine, which have a profound influence on the intrinsic excitability of motoneurons and thus control
how motoneurons process their excitatory and inhibitory inputs. In Aim 1, we create a basic version of the
human motor output map by asking subjects to generate slow linear increases and decreases in torque for
more than 20 muscles across the body. The protocol is kept exactly the same across muscles to allow
comparisons of the resulting firing patterns. Our primary hypothesis is that muscles involved in stabilization of
the body, such as proximal muscles, will generate motor unit firing patterns consistent with high levels of
neuromodulatory drive, while muscles involved more in precision tasks will generate patterns consistent with
low levels of neuromodulation. These experiments are essentially function anatomy, the proximal-distal
variations in firing patterns probably arise from differences in the anatomical projections of synaptic inputs to
motor pools. In Aim 2, we assess whether there are task dependent changes in firing patterns, such as
increases in neuromodulation drive with increased effort and increases in sensory inhibition with movement.
Taken together, these experiments will define the fundamental structure of motor output for the human
musculoskeletal structure and provide a quantitative basis for understanding the distortions tha...

## Key facts

- **NIH application ID:** 9961672
- **Project number:** 5R01NS098509-05
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Charles Heckman
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $414,500
- **Award type:** 5
- **Project period:** 2016-07-01 → 2022-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9961672

## Citation

> US National Institutes of Health, RePORTER application 9961672, The Human Motor Output Map (5R01NS098509-05). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9961672. Licensed CC0.

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