Event-related brain potentials isolate the motor component in a tapping task

Repetitive tapping is used to investigate temporal perception, memory, and reproduction. Intertap intervals and their variability, arise from cognitive and motor processes during the task. We used a measure of readiness potential onset to determine motor component latency during the timed interval. Subjects performed a paced, two-handed tapping task at four target intervals (1.5-2.75 s). Overall latency of production increased with increasing ISI, as did variability across target interval, conforming to a generalized Weber's law. In contrast, average motor latency was roughly 0.5 s across ISI. This constant motor latency may also indicate constant variability attributable to motor processing.     

Expectancy-related cerebral potentials associated with voluntary time estimation and omitted stimulus

Expectancy-related and nonexpectancy-related cerebral potentials associated with stimuli and omitted stimuli were recorded in 7 normal subjects. The stimuli were constantly delivered to the right median nerve and the interstimulus interval was set at 7 seconds. When the subject counted to estimate the interstimulus interval correctly, a slow negative deflection appeared about one second prior to both the stimuli and the omitted stimuli. In the case of the omitted stimulus, this expectancy-related negative potential (ENP) returned to the base line after several hundred msec. When the stimuli were delivered, the amplitude of the P300 was much higher when the subject was paying attention to the stimuli than when he was not. The scalp distribution of the ENP was rather anterior to the P300. No ENP appeared when the subject was not paying attention to the stimuli or the omitted stimuli, or when the stimuli were delivered at a random rate.     

Event-related slow potentials in rat cortex during a reaction time task: Cortical area differences

Event-related slow potentials were recorded from frontal and visual cortex of rats during a reaction time task in which trials were initiated at variable intervals by an auditory warning stimulus. Transcortical slow potential (SP) responses during the two-second period between onset of the warning stimulus and extension of a retractable lever were analyzed, using single trial and averaged response data. SP responses recorded from the two cortical areas differed significantly with respect to waveform and amplitude. The results indicate that event-related slow potentials from rat cortex are area dependent and that the small size of the rat brain does not preclude recording of SP changes with differential cortical distribution.     

Event-related desynchronization related to the anticipation of a stimulus providing knowledge of results.

In the present paper, event-related desynchronization (ERD) in the alpha and beta frequency bands is quantified in order to investigate the processes related to the anticipation of a knowledge of results (KR) stimulus. In a time estimation task, 10 subjects were instructed to press a button 4 s after the presentation of an auditory stimulus. Two seconds after the response they received auditory or visual feedback on the timing of their response. Preceding the button press, a centrally maximal ERD is found. Preceding the visual KR stimulus, an ERD is present that has an occipital maximum. Contrary to expectation, preceding the auditory KR stimulus there are no signs of a modality-specific ERD. Results are related to a thalamo-cortical gating model which predicts a correspondence between negative slow potentials and ERD during motor preparation and stimulus anticipation.     

The influence of time after stroke on brain activations during a motor task

After stroke, the pattern of brain activation during performance of a motor task is related to outcome. Here, we compare this relationship in the early (10-14 days) and late (at least 3 months) phases after first-ever stroke. A negative linear relationship between task-related brain activation, as measured by functional magnetic resonance imaging, and outcome is seen in several identical primary and nonprimary motor regions that is independent of time after stroke. In other words, patients with poorer outcome scores recruit more widely within motor-related regions in both the early or late poststroke phase. However, in contralesional middle intraparietal sulcus, contralesional cerebellum, and ipsilesional rostral premotor cortex, this relationship is seen only in the early poststroke phase. Thus, patients with poorer outcome scores recruit these areas in only the early and not the late poststroke phase. These results suggest that there are differences in the cerebral implementation of action in patients with poor outcome that are dependent on the time since stroke. Thus, in those patients with the most to gain from rehabilitation, different therapeutic approaches may be required at different stages after stroke.     

Neuromuscular recruitment related to stimulus presentation and task instruction during the anti-saccade task

The contextual control of movement requires the transformation of sensory information into appropriate actions, guided by task‐appropriate rules. Previous conceptualizations of the sensorimotor transformations underlying anti‐saccades (look away from a stimulus) have suggested that stimulus location is first registered and subsequently transformed into its mirror location before being relayed to the motor periphery. Here, by recording neck muscle activity in monkeys performing anti‐saccades, we demonstrate that stimulus presentation induces a transient recruitment of the neck muscle synergy used to turn the head in the wrong direction, even though subjects subsequently looked away from the stimulus correctly. Such stimulus‐driven aspects of recruitment developed essentially at reflexive latencies (～60–70 ms after stimulus presentation), and persisted at modest eccentricities regardless of head‐restraint. Prior to stimulus presentation, neck muscle activity also reflected whether the animals were preparing for an anti‐saccade or a pro‐saccade (look toward a stimulus). Neck muscle activity prior to erroneous anti‐saccades also resembled that observed prior to pro‐saccades. These results emphasize a parallel nature to the sensorimotor transformations underlying the anti‐saccade task, suggesting that the top‐down and bottom‐up processes engaged in this task influence the motor periphery. The bottom‐up aspects of neck muscle recruitment also fit within the context of recent results from the limb‐movement literature, showing that stimulus‐driven activation of muscle synergies may be a generalizing strategy in inertial‐laden systems.     

Movement-related slow potentials during motor imagery and motor suppression in humans

Electro-encephalograms (EEGs) associated with motor imagery and motor suppression were recorded from motor-related frontal regions in humans. A negative potential was observed both during motor imagery and during NO-GO responses, as well as in movement trials. The negative potentials observed in the motor imagery trials had a similar pattern to those observed in the movement trials, although the potentials were different from those during NO-GO responses. The peak amplitude of the negative potential recorded at FCz was significantly larger than those recorded at F3, F4, C3, and C4 in the imagery task. The peak amplitude of the negative component in movement trials was larger than that in the imagery trials of all recording positions. By contrast, during the GO/NO-GO task, the peak amplitude during NO-GO responses was larger than that during the GO responses at every position. It appears, therefore, that motor imagery and motor suppression are associated with their own specific internal processes which are reflected by specific EEG patterns in motor-related frontal areas.     

Preparatory slow potentials and event-related potentials in an auditory cued attention task.

OBJECTIVES: To examine reaction times and event-related potentials (ERPs) in an auditory cued attention task varying motor requirements, cue validity, and cue location.METHODS: Subjects (n=13) listened to cue-target stimulus pairs. Verbal cues (monaural, binaural) indicated the ear to receive a target tone 1.5s later. Cues correctly (valid) or incorrectly (invalid) predicted target ear, or were uninformative (neutral). In separate conditions subjects either responded by pressing one of two buttons, or did not respond to targets. ERPs for cues and targets (P50, N100, P200, late slow wave), and negative slow potentials between cues and targets were assessed.RESULTS: Target reaction times for valid cues were significantly shorter than for invalid cues, with intermediate values for neutral cues. When no motor response was required larger ERPs were seen to both cues and targets. Negative slow potentials had larger amplitudes before target presentation when subjects responded to targets; and were larger following neutral, vs. valid/invalid, cues. ERPs (N100, P200) to invalidly cued targets were significantly larger and a subsequent late slow wave was more positive, relative to validly cued targets.CONCLUSIONS: Expectancy for targets begins shortly after cue presentation, and is affected by both motor requirements and the information content of the cue. ERP amplitudes to targets are modulated by the correspondence between cue information and actual target location.     

Patterns of task-related slow brain potentials in dyslexia

Six dyslexic youths who met the Hughes and Denckla criteria of "dyslexia pure" and 10 normal control subjects were investigated with DC recordings of task-related cortical negativity using 10 leads over the right and left hemispheres. Potentials were recorded during the following tasks: reading, orthographic error detection, letter series, word assembly, word fluency, finding of antonyms, and viewing of Necker cubes. Both groups exhibited greater right hemisphere negativity during the Necker cube task. Whereas controls revealed greater left hemisphere negativity during linguistic tasks, the reverse was found with dyslexics. The right shift was pronounced with the reading, orthographic error detection, and antonym conditions. Differences between the two groups were also found for the pattern of cortical distribution. We conclude that dyslexia is associated with changes in the lateral distribution of cortical activity during certain types of language processing.     

Perceptual asymmetries in a time estimation task with emotional sounds

Four experiments investigated potential interactions between emotional content and perceptual asymmetries in the estimation of short time intervals. In all experiments, the word “bower” was presented monaurally to the left or right ear in an emotional tone and participants performed a temporal bisection task. In Experiment 1, angry and neutral stimuli ranged in duration from 260 to 440 ms (in steps of 20 ms) whereas in Experiments 2–4, durations ranged from 260 to 480 ms (in steps of 20 ms). In Experiment 3, the emotional tone of happiness replaced anger. In Experiment 4, anger and happiness were used as stimuli. In all experiments, results showed a larger bisection point for the right compared to the left ear. In addition, in all experiments, the constant error was farther away from zero for the right than for the left ear. The bisection point was also longer for the angry (Experiments 1 and 2) or happy (Experiment 3) than for the neutral emotional tone. Finally, happiness produced a shorter bisection point than anger in Experiment 4. Results are discussed in terms of their implications for time perception mechanisms and their potential cerebral representation.     

The influence of time preparation on motor processes assessed by surface Laplacian estimation

OBJECTIVE: The present study was aimed at testing whether foreperiod duration affects the activity recorded over the primary sensorimotor cortices during the reaction time. METHODS: The foreperiod duration (500 or 2500 ms) was varied across blocks of trials during a between-hand choice reaction time task; surface Laplacians were estimated from EEG recordings by the source derivation method. RESULTS: Reaction time was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod. A contralateral negativity/ipsilateral positivity pattern showed up over the primary sensorimotor cortices. The time between the contralateral negativity onset and the electromyographic onset was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod, which suggests that the foreperiod affects the implementation of the motor command. Furthermore, the interval between the onset of the voluntary electromyographic activity and the mechanical response was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod. CONCLUSIONS: These results indicate that time preparation affects both central and peripheral motor processes.     

Distribution of slow cortical potentials preceding self-paced hand and hindlimb movements in the premotor and motor areas of monkeys

Surface negative-depth positive, slowly increasing potentials prior to self-paced hand and hindlimb movements were recorded in the dorsal aspect of the motor and premotor cortices with chronically implanted electrodes. It was shown that the potentials were recorded in the contralateral forelimb motor area prior to hand movements but were hardly seen in the hindlimb motor area. On hindlimb movements, the contralateral hindlimb motor area showed the premovement potentials, whereas the forelimb motor area revealed little or no premovement potentials. The contralateral premotor cortex was shown to induce the premovement potentials in its wider areas and participate in both of hand and hindlimb movements in a similar fashion, with predominances in its dorsolateral portion for hand movements and in its dorsomedial portion for hindlimb movements respectively. In the hemisphere ipsilateral to the moving hand, the relatively large premovement slow potentials emerged frequently also in the premotor cortex, whereas only the small potential was obtained from the forelimb motor area. These results suggest that the premotor cortex (area 6) participates in the more general and associative organization of motor function than the motor cortex (area 4) which represents the specialized role in the motor performance.     

Approximate entropy of motoneuron firing patterns during a motor preparation task

The aim of this study was to test whether approximate entropy (ApEn) analysis provides a suitable method of detecting differences induced by a motor preparation task in time-ordered inter-spike intervals (ISIs) recorded in tonically firing motoneurons. Unlike classical methods of analyzing neuronal discharge variability, in which serial order is no taken into account, the approximate entropy (ApEn) was proposed by Pincus [Pincus SM. Approximate entropy as a measure of system complexity. Proc Natl Acad Sci USA 1991;88:2297-301] to analyze ordered series. ApEn statistic is a number assigned to an ordered series, where higher values correspond to greater serial irregularity. In the present study, the activity of 31 single motor units (SMUs) was recorded in human extensor carpi radialis muscles and the ISI durations were analyzed during the performance of a pre-cueing reaction time motor task involving a 3-s preparatory period. ApEn values were computed for each SMU during three steps of the preparatory period and during the preceding control period. Lower ApEn values, were found during preparatory period. The decrease in ApEn values, i.e., the increase in serial regularity, was monotonic from the control to the end of the preparatory period. These results show that ApEn model-independent statistics are a relevant means of detecting changes related to motor preparation in the regularity of time-ordered inter-spike intervals (ISIs).     

Origin of surface motor unit potentials in hypothenar motor unit number estimation

Introduction: Far‐field potentials (FFPs) from muscles other than the abductor digiti minimi (ADM) may interfere with motor unit number estimation (MUNE) from that muscle. Methods: We identified the origin of each surface motor unit potential (SMUP) during hypothenar MUNE using the multiple point stimulation method in 20 control subjects by recording from individual ulnar‐innervated muscles with a common proximal reference (pref). Results: ADM SMUPs comprised 39.0% of the accepted SMUPs, followed by those from the fourth dorsal interosseous muscle (14.0%), the fourth lumbrical muscle (9.2%), and the second and third palmar interosseous muscles (8.8% each). The percentage of ADM SMUPs varied from 18% to 73% of accepted SMUPs among individual subjects. Accepted non‐ADM SMUPs were usually much smaller than ADM SMUPs, and many more non‐ADM SMUPs were excluded due to their small size. Conclusions: A large contribution from non‐ADM or non‐hypothenar SMUPs obscures the meaning of the MUNE value. Muscle Nerve, 48: 185–190, 2013     

Event-related potentials in schizophrenic patients during a degraded stimulus version of the visual continuous performance task

Previous studies of the auditory P300 event-related potential (ERP) have reported smaller amplitudes in chronic schizophrenics but similar consistencies have not been observed with visual P300s. This study examined P300s in symptomatically stable, medicated, chronic schizophrenics (n = 14) and normal controls (n = 14) performing a visual continuous performance task utilizing degraded stimuli to burden encoding processes. Performance analysis found slower response times, fewer target detections and more false alarms in patients than in controls. Analysis of ERPs showed P300 amplitudes of schizophrenics to be significantly smaller than those of controls and, unlike controls, schizophrenics failed to exhibit significant target vs. non-target P300 amplitude differences. Discriminant analysis indicated target and non-target midline (Fz, Cz, Pz) P300 amplitudes together correctly classified all patients and controls. Exploratory topographic analysis indicated that P300 amplitudes were not asymmetrical in patients, as has been observed with auditory P300s, and, unlike the performance measures, the P300s did not correlate with the patient's positive or negative symptom ratings. The implications of these findings are described in relation to attentional disturbances and trait versus state issues in schizophrenics.     

Automaticity in attractive face processing: brain potentials from a dual task

Attractive faces have a special status, possibly because of evolutionary reasons. We assessed the automaticity of facial attractiveness processing in a dual-task paradigm manipulating the availability of cognitive resources to face processing by a primary tone task presented at varying stimulus onset asynchrony (SOA). In event-related brain potentials, attractive relative to neutral faces induced an increased posterior negativity from 260 ms onwards indicating enhanced stimulus encoding at the cortical level. Interestingly, effects of attractive faces on event-related brain potentials were most pronounced at high temporal overlap with the primary task (short stimulus onset asynchrony). This indicates that a shortage of cognitive resources may enhance the processing of attractive faces, revealing hard-wired processing biases of the human information processing system for evolutionarily prepared stimuli.     

Habituation in a simple repetitive motor task: a study with movement-related cortical potentials.

OBJECTIVE: The movement-related cortical potential (MRCP) attenuates over the right hemisphere during the performance of a complex motor sequence. Because subjects have to learn complex sequences, earlier research has attributed this decrease of negativity to motor learning. The aims of this study were (1) to examine whether such an attenuation also occurs in the course of a repetitive motor task so simple that learning is not required, and (2) whether there are any transfer effects when subjects change from one to the other hand. METHODS: MRCPs were recorded in 33 right-handed healthy subjects. In a counterbalanced crossover design, subjects made 100 self-paced unilateral button presses with their left or right index finger, and then continued on the other side of the body for another 100 movements. Tasks were performed with the same speed during the entire experiment. RESULTS: (1) The amplitude of the MRCP attenuated over the right hemisphere in the course of the tasks irrespective of the side of movement. (2) The amplitude of the MRCP decreased across the entire scalp until a minimum level was reached at the end of the earlier sequence, and then increased slightly from this low level during the following sequence made after a switch of hand. CONCLUSIONS: The right hemisphere may predominate motor activation or attentional demands directed towards movement execution or somatosensory inputs even in very simple motor tasks. The decrease and subsequent increase of negativity during the first and second sequence, respectively, may reflect the subjects' changing arousal.