Jozina B. De Graaf

Error processing during online motor control depends on the response accuracy

We investigated which brain areas show error-related activity during online motor control while errors occur independently from decision making. During motor tasks, error is a deviation from accuracy or correctness. The effect of the accuracy level on error-related brain activity is unclear. Using functional Magnetic Resonance Imaging (fMRI), we investigated how error-related brain activity, especially in fronto-medial wall areas, depended on motor accuracy (MA). Subjects performed a force tracking task with the thumb-index grip: to continuously follow a moving target on a monitor with a cursor which position was controlled by the force amount produced by the fingers. Task difficulty varied with changes in the cursor size (the smaller the cursor, the more difficult the task). We measured the motor accuracy (mean distance between the cursor center and the target) and the error amount (cursor out of the target). Errors were produced when motor accuracy was low and also when motor accuracy was high. For fMRI data processing, we defined a model based on both the error amount and the motor accuracy. The results showed that supplementary motor area (SMA) and dorsal anterior cingulate cortex (ACC) activation increased with error and task difficulty independent of the accuracy of motor control. Interestingly, activity in the rostral part of left ACC only increased with error when the motor accuracy was low, independently from task difficulty. These results suggest a clear functional dissociation between dorsal and rostral ACC in error processing which depends on the amount of attentional resources allocated to motor accuracy.

Functional corticospinal projections from human supplementary motor area revealed by corticomuscular coherence during precise grip force control.

The purpose of the present study was to investigate whether corticospinal projections from human supplementary motor area (SMA) are functional during precise force control with the precision grip (thumb-index opposition). Since beta band corticomuscular coherence (CMC) is well-accepted to reflect efferent corticospinal transmission, we analyzed the beta band CMC obtained with simultaneous recording of electroencephalographic (EEG) and electromyographic (EMG) signals. Subjects performed a bimanual precise visuomotor force tracking task by applying isometric low grip forces with their right hand precision grip on a custom device with strain gauges. Concurrently, they held the device with their left hand precision grip, producing similar grip forces but without any precision constraints, to relieve the right hand. Some subjects also participated in a unimanual control condition in which they performed the task with only the right hand precision grip while the device was held by a mechanical grip. We analyzed whole scalp topographies of beta band CMC between 64 EEG channels and 4 EMG intrinsic hand muscles, 2 for each hand. To compare the different topographies, we performed non-parametric statistical tests based on spatio-spectral clustering. For the right hand, we obtained significant beta band CMC over the contralateral M1 region as well as over the SMA region during static force contraction periods. For the left hand, however, beta band CMC was only found over the contralateral M1. By comparing unimanual and bimanual conditions for right hand muscles, no significant difference was found on beta band CMC over M1 and SMA. We conclude that the beta band CMC found over SMA for right hand muscles results from the precision constraints and not from the bimanual aspect of the task. The result of the present study strongly suggests that the corticospinal projections from human SMA become functional when high precision force control is required.

Inkjet-Printed PEDOT:PSS Electrodes on Paper for Electrocardiography

Inkjet-printed PEDOT:PSS electrodes are shown to record cutaneous electrophysiological signals such as electrocardiograms via a simple finger-to-electrode contact. The recordings are of high quality and show no deterioration over a 3 month period, paving the way for the development of the next generation of low-cost, convenient-to-use healthcare monitoring devices.

TMS reveals a direct influence of spinal projections from human SMAp on precise force production

The corticospinal (CS) system plays an important role in fine motor control, especially in precision grip tasks. Although the primary motor cortex (M1) is the main source of the CS projections, other projections have been found, especially from the supplementary motor area proper (SMAp). To study the characteristics of these CS projections from SMAp, we compared muscle responses of an intrinsic hand muscle (FDI) evoked by stimulation of human M1 and SMAp during an isometric static low‐force control task. Subjects were instructed to maintain a small cursor on a target force curve by applying a pressure with their right precision grip on a force sensor. Neuronavigated transcranial magnetic stimulation was used to stimulate either left M1 or left SMAp with equal induced electric field values at the defined cortical targets. The results show that the SMAp stimulation evokes reproducible muscle responses with similar latencies and amplitudes as M1 stimulation, and with a clear and significant shorter silent period. These results suggest that (i) CS projections from human SMAp are as rapid and efficient as those from M1, (ii) CS projections from SMAp are directly involved in control of the excitability of spinal motoneurons and (iii) SMAp has a different intracortical inhibitory circuitry. We conclude that human SMAp and M1 both have direct influence on force production during fine manual motor tasks.

Cognitive Integration in the Human Primary Sensory and Motor Areas: An Overview

Although many different definitions of cognition exist, there is a general acceptance that cognition can be defined as a higher function with respect to both the primary stages of sensory information processing and the final stage of motor output. This idea has been the basis of many well known psychological models where one can identify “input boxes” (i.e., visual, auditory, somatosensory information), and “output boxes” (i.e., motor commands), with, intermediate, high level (attention, language, memory, ...) and low-level (motor intention, preparation) cognitive functions (see, for instance, the information processing model of Smidt and Lee (2005), or the model for central representation of goal-directed movements of Jeannerod (1990)). Although these models are, without doubt, well suited to the study of cognitive processes from a psychological standpoint, they are not very helpful from a neuroscientific point of view. Indeed, ever since the very first investigations into the functioning of the living brain, the main aim has been to localize cognitive functions into the cortical structures of the brain. There exist at least two problems related to this approach. Firstly, and this is not a recent objection (e.g., Posner and Raichle (1998) page 16), it is doubtful whether the cognitive functions as presently conceived have a meaning for the brain. Let us take for example the so-called “eye-hand coordination”. This “function” is much studied today and many publications report attempts to localize it in the brain. But, for a normally developed brain, this is not a specific function which is needed at specific moments and which is necessarily implemented in a specific brain structure. All input is continuously put in relation with each other as a function of the particular output. It seems more likely that eye-hand coordination is controlled in a continuous, implicit and distributed way. It is pertinent here to mention the ecological approach of perception (Gibson, 1986). This approach is based on the concept of “affordance” that characterizes the object of perception as a whole of many possible actions and interactions, and is in rupture with the cognitive approach. Indeed, according to the latter approach, the brain organizes the perception of the world, whereas in the ecological approach, the world organizes the perception: The role of the brain is to extract the information presented by the world. This theory suggests that the traditional approach of studying cerebral functioning is not very appropriate: the cognitive functions that we define do not have much sense for the brain and, what’s more, we generally put subjects in

Reachability and the sense of embodiment in amputees using prostheses

Amputated patients are hardly satisfied with upper limb prostheses, and tend to favour the use of their contralateral arm to partially compensate their disability. This may seem surprising in light of recent evidences that external objects (rubber hand or tool) can easily be embodied, namely incorporated in the body representation. We investigated both implicit body representations (by evaluating the peripersonal space using a reachability judgement task) and the quality of bodily integration of the patient’s prosthesis (assessed via questionnaires). As expected, the patients estimated that they could reach further while wearing their prosthesis, showing an embodiment of their prosthesis in their judgement. Yet, the real reaching space was found to be smaller with their prosthesis than with their healthy limb, showing a large error between reachability judgement and actual capacity. An overestimation was also found on the healthy side (comparatively to healthy subjects) suggesting a bilateral modification of body representation in amputated patients. Finally, a correlation was found between the quality of integration of the prosthesis and the way the body representation changed. This study therefore illustrates the multifaceted nature of the phenomenon of prosthesis integration, which involves its incorporation as a tool, but also various specific subjective aspects.