Which part of the motor cortex is responsible for executing the voluntary movement?

Sources

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Purves, D., Augustine, G. and Fitzpatrick, D. (2001) ‘The premotor cortex’, in Neuroscience. 2nd edn. Available at: https://www.ncbi.nlm.nih.gov/b....

Yip, D.W. and Lui, F. (2021) ‘Physiology, Motor Cortical’, StatPearls. Available at: https://www.ncbi.nlm.nih.gov/b....

Crossman, A.R. and Neary, D. (2010) Neuroanatomy: An illustrated colour text. 4th edn. Churchill Livingston Elsevier.

39.4.4 Variability and Asymmetry

First, variability values rose sharply (Figure 39.14) from 4–5 mm in primary motor cortex to localized peaks of maximum variability in posterior perisylvian zones and superior frontal association cortex (16–18 mm). Temporal lobe variability rose from 2–3 mm in the depths of the Sylvian fissure to 18 mm at the posterior limit of the inferior temporal sulcus in both brain hemispheres. Peak variability occurs in the vicinity of functional area MT [126] and extends into the posterior heteromodal association cortex of the parietal lobe (14–18 mm). Second, there is a marked anatomic asymmetry in the posterior perisylvian cortex ([52]; up to 10 mm). This asymmetry is not clearly apparent individually, but appears clearly in the average representation. It also contrasts sharply with negligible asymmetry in the frontal, parietal, and occipital cortex (1–2 mm). Similar studies of deep sulcal cortex found this asymmetry to be greater in Alzheimer's patients than in controls matched for age, gender, handed-ness, and educational level, corroborating earlier reports of an asymmetric progression of the disease [115]. The improved ability to localize asymmetry and encode its variability in a disease-specific atlas has encouraged us to develop a probabilistic atlas of the brain in schizophrenia [85] where cortical organization and functional lateralization are also thought to be altered ([68]; cf. [25]).

12.5.2 Channel selection and data segmentation

Channel selection is applied to reduce the system complexity and make the process faster. The finger movement task is controlled by primary motor cortex. Therefore, information level in all the ECoG recordings will differ which insists to select the significant channels. In this method, subject specific correlation is used for channel selection in which correlation coefficient between each channel is computed for each subject with different trial. A binary threshold (th) is applied in correlation matrix to get the highly correlated channels.

(12.12)HCE=HCif corr≥thLCif corr<th

where “th” is threshold. In this method, the value of th is taken as 0.7 (HCE—highly correlated experiments and corr—correlation). In this manner, channel combinations of high correlation (HC) and low correlation (LC) are received. Thereafter, the channel ranking is applied for selecting the significant channels. Thereafter, each channel is observed and counted the number of HC values for all the experiments. A ranking is done on the basis of number of HC values for each channel. Highly correlated 11 channels are finally considered for decomposition and feature computation. The channel selection method is explained in which correlation based HC/LC is defined for each channel with respect to all 23 experiments. Thereafter, total number of HC values is counted for all experiments. Finally, all the channels are arranged in descending order with respect to number of HC which are shown in last column of Table 12.1. The top ordered 11 channels are selected for further processing. The proposed subject specific channel selection method is used for all three subjects.

Table 12.1. The number of HC count for subject 3 index finger using all 23 experiment results.

After performing the channel selection, the long term ECoG signal is segmented into short duration signals. This way, the time complexity is reduced in VMD based signal decomposition. In the proposed method, complete recording is segmented into every 1 s duration signals.

Abstract

The somatic nervous system provides control of skeletal muscle movement. Conscious control of movement originates in the motor cortex (both premotor and primary motor cortex). However, movement is refined and coordinated by various structures in the CNS, including extrapyramidal regions and the cerebellum. Furthermore, spinal reflexes also modulate motor function. Ultimately, the contraction of muscle is induced by activation of motoneurons that innervate skeletal muscle. Electrical impulses from these neurons are converted to a chemical message at the neuromuscular junction, where the neurotransmitter ACh is released by the motoneuron. Numerous diseases of motor control arise from either defects in the CNS, the peripheral neurons (motoneurons) or the muscle itself. Various drugs can influence motor control by acting on the CNS or in the periphery.

Convergent Circuits

There are many local circuits in the cortex where different regions have convergent projections into a single site or ‘node.’ An example is the primary motor cortex. The primary motor cortex provides the main source of control over alpha motor neurons in the spinal cord for the control of skilled movement. What shapes the activity of the motor cortex? Brain imaging studies show that the primary motor cortex is anatomically connected with many different premotor cortical areas; and represents a critical point of information convergence (Figure 6). Critically, no single premotor area has a privileged position as a ‘supramotor’ center (Dum and Strick, 2002). Instead, anatomic connectivity studies demonstrate that the different premotor areas all interact with each other and all project into primary motor cortex. This convergent architecture allows for motor commands to be generated from different sources, depending on task requirements and the context of behavior.

11.3.3.1 Electrode Array Implantation Surgery

A single array composed of 100 silicon microelectrodes in a 10 × 10 grid (Blackrock Microimplantable Systems, Inc.) was chronically implanted in the hand area of the primary motor cortex (M1). A craniotomy was performed above M1, and the dura was incised and reflected. The electrode array was positioned on the crown of the right precentral gyrus, approximately in line with the superior ramus (medial edge) of the arcuate sulcus. In most cases, we used interoperative stimulation of the exposed cortical surface to determine the optimal implant site. A piece of artificial pericardium was applied above the array, the dura was closed using 4.0 Nurolon sutures, and another piece of pericardium was applied over it. The excised bone flap was replaced, and the skin was closed.

ABSTRACT

Proprioception refers to sensory inputs that principally regulate motor control, such as inputs that signal muscle stretch and tension. Proprioceptive cortex includes part of SI cortex (area 3a) as well as part of primary motor cortex. We propose a computational model of neocortex receiving proprioceptive input, a detailed map of which has not yet been clearly defined experimentally. Our model makes a number of testable predictions that can help guide future experimental studies of proprioceptive cortex. They are first, overlapping maps of both individual muscles and of spatial locations; second, multiple, redundant representations of individual muscles where antagonist muscle length representations are widely separated; third, neurons tuned to plausible combinations of muscle lengths and tensions; and finally, proprioceptive “hypercolumns, ” i.e., compact regions in which all possible muscle lengths and tensions and spatial regions are represented.

Review Questions

1.

What neurons directly control muscle contraction? Where are the cell bodies of these neurons?

What is a motor unit? How is muscle contraction graded?

What is the primary motor cortex? Where is the sensory association area? Where is the premotor cortex and the supplementary motor cortex? What is the somatotopic mapping of motor control?

What role does the spinal cord play in control of movement?

What happens when there is damage to the sensory association area?

Name the basal ganglia. What is the major input to the caudate nucleus? To the putamen?

What is the direct pathway? Does it promote or inhibit wanted effort? How does it do this?

What is the indirect pathway? Does it promote or inhibit wanted effort?

What role does the substantia nigra play in the control of movement by the basal ganglia? What disease is association with dysfunction of the substantia nigra?

What information is carried by the mossy fibers? The climbing fibers? What happens when cerebellar function is compromised?

What is the endolymph? What is the perilymph? How do hair cells detect acceleration? Where is the information processed in the CNS?

3.2.4 Motor and Sensory Areas

The major motor and sensory areas are separated by the central sulcus and the immediate areas anterior (precentral gyrus) and posterior (postcentral gyrus), forming, respectively, the primary motor and sensory cortices. Neurons within the primary motor cortex control voluntary movement by controlling somatic motor neurons in the deep brain and spinal cord, while neurons within the primary sensory cortex receive somatic sensory information from afferent neurons located within the skin and muscle that detect changes in pressure, pain vibration, taste, and temperature.

The organization of the primary motor cortex can be described like the keys on a piano. When struck, the piano keys produce a distinct sound and a collection of sounds in the right order produces music, rather than just random noise. Similarly, the primary motor cortex is mapped in such a way that each region controls a specific muscle. When stimulated electrically or magnetically, a muscle contraction may be observed in that specific skeletal muscle in which it is controlling. To help better understand how the primary motor cortex controls voluntary muscle, the idea of a “motor homunculus” was developed to depict the level of organization and contribution of the primary motor cortex in muscle control (Fig. 3.1). Similarly, the primary sensory cortex is organized in a manner that mirrors the motor homunculus. Like monitoring gauges in the dashboard of a car, the primary sensory cortex report key information regarding touch, pain, pressure, vibration, taste, and temperature. Other sensory information, such as sight, sound, smell, and taste are controlled by other parts of the cerebral cortex, such as the visual cortex of the occipital lobe, and the auditory and olfactory cortex in the temporal lobe.

3.6.1 The cognitive system

Cognitive abilities of natural intelligence process are supported by specific neuronal networks. Human being has a motor hierarchy that functions in an interdependent way: The spinal cord and brainstem are involved in processing the activity of individual muscles such as walking and reflex actions that initiate consciously. There are also the third and fourth levels of that hierarchy:

Voluntary movements require the participation of the third and fourth levels of the hierarchy: the motor cortex and the association cortex. These areas of the cerebral cortex plan voluntary actions, coordinate sequences of movements, make decisions about proper behavioral strategies and choices, evaluate the appropriateness of a particular action given the current behavioral or environmental context, and relay commands to the appropriate sets of lower motor neurons to execute the desired actions.

(Knierim, 2020, n.p.).

The motor cortex comprises: The primary motor cortex, premotor cortex, and supplementary motor area:

The motor cortex comprises three different areas of the frontal lobe, immediately anterior to the central sulcus. These areas are the primary motor cortex (Brodmann’s area 4), the premotor cortex, and the supplementary motor area […]. Electrical stimulation of these areas elicits movements of particular body parts. The primary motor cortex, or M1, is located on the precentral gyrus and on the anterior paracentral lobule on the medial surface of the brain. Of the three motor cortex areas, stimulation of the primary motor cortex requires the least amount of electrical current to elicit a movement. Low levels of brief stimulation typically elicit simple movements of individual body parts. Stimulation of premotor cortex or the supplementary motor area requires higher levels of current to elicit movements, and often results in more complex movements than stimulation of primary motor cortex. […] the premotor cortex and supplementary motor areas appear to be higher level areas that encode complex patterns of motor output and that select appropriate motor plans to achieve desired end results.

(Knierim, 2020, n.p.).

The classical neuroscience defines the brain motor scheme covering the following areas and functions: Broca area; sensory area; somatosensorial area; auditive area; visual area; Wernicke area; association area; prefrontal cortex (superior mental functions: representation, planning, and execution of the actions; cognition; behavior and emotional control; environment adaptation; working memory). The Figs. 5 and 6 illustrate this classification.

The complexity of cognition system led, in a fMRI study, Benjamin et al. (2017) to identify multiple language-critical areas that includes Broca’s and Wernicke Area (inferior and superior), Exner’s Area, Supplementary Speech Area, Angular Gyrus, and Basal Temporal Language Area.

Although classical doctrine relates some areas of the brain to language, we propose in this book to think of language linked to natural intelligence. In this way, natural language is conceived as a complex system that goes beyond the network of neurons and supporting cells to provide an understanding (natural intelligence) of the world involving functional mechanisms such as thought, memory, emotion, and sleep.

It is proposed to understand natural language as the system that involves since the capture (input) of the external stimulus made by the body, the passage through the central cognitive system (natural intelligence) that transforms the stimulus into mental representation and exit (output) by human action, all of them working together as an integrated whole.

The nervous system is traditionally divided into three principal anatomic units: the central nervous system (CNS), the peripheral nervous system (PNS), and the autonomic nervous system (ANS).These systems are not automatically or functionally distinct, and they work together as an integrated whole. Therefore, when function […] the nervous system is more conveniently divided into sensory, motor, and higher brain functions.

[…] The CNS includes the brain and the spinal cord. Its primary functions are receiving and processing sensory information and creating appropriate responses to be relayed to muscles and glands. It is the site of emotion, memory, cognition, and learning. The CNS is bathed in cerebrospinal fluid (CSF) [and] interacts with the neurons of PNS through synapses in the spinal cord and cranial nerve glia. The cranial and spinal nerves constitute the PNS.

(Copstead and Banasik, 2013, p. 858).

The peripheral nervous systems comprise 31 pairs of spinal nerves and 12 pairs of cranial nerves. Certain areas of the cerebral cortex are associated with specific functions: Frontal lobe is in charge of complex thought, motivation, and morality; the temporal lobe encompasses the auditory center and parts of the language center; the occipital lobe is linked to visual functions; the parietal lobe contains the somatosensory cortex; the limbic area is responsible for memory and emotion (Copstead and Banasik, 2013, p. 877) (Figs. 7 and 8).

The body is somatotopically represented by the spinal cord and the cerebral cortex as taught by Copstead and Banasik (2013, p. 891):

Projections to the somatosensory cortex begin in sensory receptors throughout the body. Receptors send axons to the spinal cord through the dorsal root. Stimulations of the receptors by mechanical deformation, temperature, or chemical alters membrane permeability, resulting in receptor potentials. The intensity of the stimulus is reflected in the rate of action potentials generated.

(Copstead and Banasik, 2013, p. 891).

Stimulation of the primary motor results in movements that travel, crossing the spinal cord through neuronal connections, which produce reflexive alterations in muscle contraction. This is a response to sensory information (Copstead and Banasik, 2013, p. 895) (Fig. 9).

According to Copstead and Banasik (2013, p. 895), although science recognizes that the cerebral cortex is “integral to the elaboration of complex thought, learning, memory, and so-called higher brain functions,” little is known about the way the brain fulfills these higher functions. Gallagher (2017, p. 15), on this subject, defends the theory of Enactivism (holistic conception of cognition involving body-brain-environment) in which the body, using the motor control or forward control mechanism “enacts (or re-enacts) a process […] coupled to a new cognitive action.” He (Gallagher, 2017, p. 15) argues that cognitive states like imagining or remembering do not begin in a representational process:

In remembering, for example, there may be reactivation of perceptual neural processes that had been activated during the original experience. It has also been shown, using electromyography (EMG) that other non-neural bodily processes, e.g., subliminal tensing of muscles and facial expressions, may be (re)activated in cases of remembering, imagining, reflecting, etc.

(Gallagher, 2017, p. 15).

On the other hand, natural intelligence in our view constitutes a process that encompasses a symbolic system, which gives rise to a representation “translating” bodily processes into values or meanings. In this way, bodily processes are represented mentally by mental signs with respective semantic properties, as we explain in more detail in Section 3.6.2.