The effects of response parameters on CNV amplitude

Attempted Arm and Hand Movements can be Decoded from Low-Frequency EEG from Persons with Spinal Cord Injury

We show that persons with spinal cord injury (SCI) retain decodable neural correlates of attempted arm and hand movements. We investigated hand open, palmar grasp, lateral grasp, pronation, and supination in 10 persons with cervical SCI. Discriminative movement information was provided by the time-domain of low-frequency electroencephalography (EEG) signals. Based on these signals, we obtained a maximum average classification accuracy of 45% (chance level was 20%) with respect to the five investigated classes. Pattern analysis indicates central motor areas as the origin of the discriminative signals. Furthermore, we introduce a proof-of-concept to classify movement attempts online in a closed loop, and tested it on a person with cervical SCI. We achieved here a modest classification performance of 68.4% with respect to palmar grasp vs hand open (chance level 50%).

Response retrieval and motor planning during typing

Recent work in language production research suggests complex relationships between linguistic and motor processes. Typing is an interesting candidate for investigating further this issue. First, typing presumably relies on the same distributed left-lateralized brain network as handwriting and speech production. Second, typing has its own set of highly specific motor constraints, such as internal keystroke representations that hold information about both letter identity and spatial characteristics of the key to strike. The present study aims to further develop research on typed production, by targeting the dynamics between linguistic and motor neural networks. Specifically, we used a typed picture-naming task to examine the interplay between response retrieval and motor planning. To track processes associated with both linguistic processing and keystroke representation, we manipulated, respectively, the semantic context in which the target appeared and the side of the first keystrokes of the word. We recorded high-density electroencephalography (EEG) continuously from the presentation of a picture, to the typing of its name, and computed both event-related potentials (ERP) and beta-band power analyses. Non-parametric data-driven analysis revealed a clear pattern of response preparation over both hemispheres close to response time, in both the ERP and beta-band power modulations. This was preceded by a left-lateralized power decrease in the beta-band, presumably representing memory retrieval, and an early contrast in ERP, between left and right keystrokes' preparation. We discuss these results in terms of a dynamic access approach for internal keystroke representations, and argue for an integrative rather than separatist view of linguistic and motor processes.

(Don't) Mind the effort: Effects of contextual interference on ERP indicators of motor preparation

Motor learning is associated with a decrease in frontal control-related brain activity and increase of central and parietal motor-related activity. Contextual interference (CI), manipulated typically by blocked versus randomized training schedules, affects motor learning, resulting in inferior performance during training but in superior performance during retention and transfer. The CI effect is often explained by increased processing demands under high CI training. Consistently, in the motor preparation phase, the activity of control- and attention-related brain areas is increased under high CI. Here, we investigated the effect of CI on learning-related changes in ERPs during motor preparation. Participants learned throwing at virtual targets and were tested for retention in the target condition 1 week later. The frontal P3 component decreased with learning during the first session and across sessions. In addition, there was a trend for a stronger reduction of P3 during retention after high CI training. Both initial and late contingent negative variation (iCNV and lCNV) amplitudes decreased with learning and showed a significantly stronger reduction under high CI. We conclude that CI modulates the interplay of cognitive and motor processes in the preparatory phase of motor learning and that a stronger involvement of cognitive processes during high CI training accounts for differential effects of CI on ERP indicators of motor preparation during retention.

Effects of response sequence length on motor programming: a chronometric analysis

The present experiment studied choice response context effects on the programming of response sequences using behavioural and electrophysiological methods. Participants were asked to produce responses differing in sequence length (1-key vs. 3-key responses) with either their left or right hand in a choice reaction time (RT) task. The choice response context was manipulated by a blocked or mixed execution of 1-key and 3-key responses. A sequence length effect on RT was observed in the blocked but not in the mixed condition. The time course of the lateralized readiness potential indicates a motoric locus of the sequence length effect, suggesting that the response hand is activated before the entire motor program is established.

The effect of response type (motor output versus mental counting) on the intracerebral distribution of the slow cortical potentials in an externally cued (CNV) paradigm

OBJECTIVE

Previous surface CNV studies including a hand motor output have suggested that the late phase of the CNV reflects the preparation of the sensorimotor cortices involved in the motor output given the same similarity in scalp potential distribution with readiness potential. However, the poor spatial resolution of the scalp recorded CNV data prevented a definitive conclusion. This intracerebral study allowed us to test this hypothesis using a CNV paradigm in which a non-motor task is used as a reference. This study concerned the intracerebrally located generators of the Contingent Negative Variation in two different paradigm settings: (i) motor output required, (ii) silent counting required (non-motor control condition).

METHODS

Stereoelectroencephalography (SEEG) recordings of the contingent negative variation (CNV) in a somato-somatosensory stimulation paradigm with a motor or counting task were taken from nine patients with drug-resistant epilepsy. The intracerebral recordings were taken from 25 cortical areas in both hemispheres (supplementary motor area-SMA; the cingulate gyrus; the orbitofrontal, premotor and dorsolateral prefrontal cortices; lateral temporal cortex, amygdalohippocampal complex; and the parietooccipital cortex).

RESULTS

The slow waves were generated in the SMA, the premotor, dorsolateral, and orbitofrontal cortices, the cingulate gyrus, and parts of the lateral temporal, mesial temporal structures and parietal cortex. We found a significant difference between the two tasks in the CNV potential generation. The task with the motor output produced significantly higher numbers of CNV potential generators when compared to the task with silent counting.

CONCLUSIONS

The CNV potential generators varied between motor and non-motor tasks. The intracerebral distribution of the potentials linked with expectation is task dependent. Our main conclusion is that the executive network is more active during the motor task than during counting task.

Contralateral and ipsilateral motor activation in visual simple reaction time: a test of the hemispheric coactivation model

Motor potentials contralateral versus ipsilateral to the responding hand were examined in a visual simple reaction time (RT) experiment in order to test the hemispheric coactivation model of Miller (Cogn Psychol 49:118-154, 2004). Visual stimuli were presented on the left side of fixation, on the right side, or on both sides, and in the RT task participants had to respond as quickly as possible to the onset of any stimulus. The same stimulus displays were also presented in a counting task, for which participants had merely to count the stimuli. Hemisphere-specific movement-related potentials contralateral and ipsilateral to the responding hand were isolated by subtracting count-task ERPs from RT-task ERPs. Consistent with the hemispheric coactivation model, there was evidence of movement-related ipsilateral positivity as well as contralateral negativity, suggesting that the motor areas of both hemispheres contribute to response initiation in simple RT. The distinction between contralateral and ipsilateral motor activation appears useful in clarifying the roles of the two hemispheres in response initiation.

The lack of focused anticipation of verbal information in stutterers: a magnetoencephalographic study

The motivation of this work was to investigate stuttering--a disorder of speech motor control--in the light of preparatory neural activity of voluntary movements related to speech. To this end, brain activity was recorded with a whole cortex magnetoencephalograph (MEG) in developmental stutterers and nonstutterers while three different tasks of single-word reading were performed. Visually presented words had to be silently read immediately after word presentation (condition 1), spoken aloud immediately after word presentation (condition 2), or spoken aloud after a delay of 1.3 s as indicated by a second visual stimulus (condition 3). Condition 2 clearly showed marked neurophysiological differences between stutterers and nonstutterers. Only nonstutterers showed clear neural activity before speech onset, which is interpreted as being linked to visual word presentation and to reflect focused verbal anticipation. This prespeech activity might reflect the "Bereitschaftsfeld2" (BF2) that is the later component of the "Bereitschaftsfeld", a well-known preparatory activity described for many other voluntary movements. Our results strongly link the lack of such preparatory brain activity at the single-word level to the disability of fluent speech in stutterers. The present results strongly support the notion that stuttering is related to impaired focused attention or anticipation.

Topographical analysis of stimulus-related and response-related electrical scalp activity and interhemispheric dynamics in normal humans

It is believed that reaction time estimates of interhemispheric relay (IHR) time or accuracy cost reflect motor relay and that visual evoked response potential (ERP) estimates reflect visual relay. If this is so, then response-related ERP estimates of IHR might be expected to correlate more with reaction time (RT) estimates of IHR than visual ERPs do, and the former ought to interact with the latter. A simple reaction time experiment (Poffenberger paradigm) was carried out with an 18-electrode montage on 10 normal subjects to investigate visual and motor interhemispheric relay effects and their interrelation. Three components in stimulus-synchronized and three other components in response-synchronized averaged signals were analyzed. Latencies and amplitudes of these components were studied as a function of the visual field stimulated and the hand required to respond. Effects interpretable as interhemispheric relay effects were observed in stimulus-related as well as response-related components. Few interhemispheric relay effect estimates in stimulus-related and response-related electrical scalp potentials were related to behavioral estimates of interhemispheric relay effects (derived from reaction times and omission errors). The spatiotemporal distributions of the electrical interhemispheric relay effects differed in stimulus and response-related components and they were statistically unrelated. We conclude that sensory interhemispheric relay may be picked up with stimulus-synchronized ERPs whereas motor interhemispheric relay effects may be measurable with response-related ERPs in normal humans. However, this proposal ought to be tested with callosotomized subjects.

High resolution spatiotemporal analysis of the contingent negative variation in simple or complex motor tasks and a non-motor task

OBJECTIVES

Since the characteristics of the Bereitschaftspotential (BP) - voluntary movement paradigm of internally-driven movements - have been established recently by our group using high resolution DC-EEG techniques, it was of great interest to apply similar techniques to the other slow brain potential--contingent negative variation (CNV) of externally-cued movements--with the same motor tasks using the same subjects.

METHODS

The CNV for simple bimanual sequential movements (task 1), complex bimanual sequential movements (task 2) and a non-motor condition (task 3) was recorded on the scalp using a 64 channel DC-EEG in 16 healthy subjects, and the data were analyzed with high resolution spatiotemporal statistics and current source density (CSD).

RESULTS

(1) The CNV was distributed over frontal, frontocentral, central and centroparietal regions; a negative potential was found at the frontal pole and a positive potential was found over occipital regions. (2) CNV amplitudes were higher for task 2 than for task 1, and there was no late CNV for task 3. (3) A high resolution spatiotemporal analysis revealed that during the early CNV component, statistical differences existed between the motor tasks (tasks 1 and 2) and the non-motor task (task 3), which occurred at frontocentral, central, centroparietal, parietal and parieto-occipital regions. During the late CNV component, additional significant differences were found not only between the motor tasks and the non-motor task but also between motor task 1 and task 2 at frontocentral, central and centroparietal regions. (4) Comparison of the CNV between the frontomesial cortex (situated over the supplementary/cingulate areas, SCMA) and both lateral pre-central areas (situated over the primary motor areas, MIs) showed that there was no statistically significant difference between the two cortical motor areas except for the early CNV. (5) Comparison of the CNV between the 3 tasks over the cortical motor areas showed that there were significant differences between the motor tasks and the non-motor task regarding the auditory evoked potential (AEP) and the early CNV component, and between all 3 tasks in the late CNV, the visual evoked potential (VEP(2)) and the N-P component. (6) The ranges and the densities of the CSD maps were larger and higher for complex than for simple tasks. The current sinks of the AEP and the early CNV were located at Fz, the late CNV at FCz and surrounding regions. As to be expected, current sources of the VEPs were located at the occipital lobes. The CNV was a current sink (negative) except for the VEP's main component which was a current source (positive).

CONCLUSIONS

(1) The CNV topography over the scalp varied with the complexity of motor tasks and between motor and non-motor conditions. (2) The origin of the early CNV may rest in the frontal lobes, while the late CNV may stem from more extensive cortical areas including SCMA, MIs, etc. (3) The late CNV component is not identical with the BP.

Response complexity and precue interval effects on the lateralized readiness potential

Fundamental properties of an important new tool in cognitive electrophysiology, the lateralized readiness potential (LRP), were examined in two experiments. Experiment 1 resolved an apparent inconsistency in the literature by demonstrating that this response-specific lateralization is larger preceding complex then preceding simple finger movements. In Experiment 2, the foveally presented precue, which indicated hand of response, preceded the go/no-go stimulus by 0, 100, 300, or 1,400 ms. Analyses of LRP latency indicated that hand-specific preparation began earlier with longer foreperiods but was temporally linked to the reaction stimulus as well as the precue. Although the degree of lateralization did not predict reaction speed in either study, a nonlateralized, response-locked negativity was larger prior to faster reactions.

Interhemispheric differences in the planning and execution of sequences of skilled finger movements

An index-middle finger (double) tapping task was used to examine hemispheric differences in the planning and execution of skilled finger movements. In two experiments, subjects responded to a simple cue presented tachistoscopically in the left or right visual field, by performing a predetermined number of double taps, (between one and eight inclusive), with either the left or right hand. Reaction times (RT) increased linearly as a function of increasing number of taps, when response sequences were controlled by the left hemisphere. In contrast, an inverse quadratic trend was obtained with right hemisphere control. When both hemispheres were involved in the stimulus-response sequence, the latency function incorporated elements of both trends, suggesting interaction between the hemispheres. The RT trends reflect differences in motor planning between the hemispheres. The conditions engaging only the right or left hemispheres did not differ in motor execution, as measured by tapping duration, variability or errors. However, when both hemispheres were involved there was evidence of interaction, which was evident as interference when the right visual field or left hemisphere was cued but the motor response was under the control of the right hemisphere (left hand). Overall, the results indicate that hand differences in fine motor skill may be determined by hemispheric differences associated with motor preparation rather than response execution.

Event-related potential indices of speech motor programming in stutterers and non-stutterers

CNVs were recorded from stutterers and non-stutterers prior to spoken words which varied according to the number of syllables, whether the words were the same or different on each trial, and the degree of repetition within the word. The effects of these response parameters on slow potential activity recorded over the speech motor area were evident both prior to, and also during, the response, suggesting that the slow potentials were reflecting both speech pre-programming and ongoing programmed control. Differences between groups were only evident prior to the response, particularly when words were familiar and therefore likely to be entirely pre-programmed. This suggests that stutterers have difficulty in setting up the parameters of the response, rather than in ongoing programmed control.