Temporal organization of covert motor processes during response selection and preparation

Speed, accuracy, and serial order in sequence production

The production of complex sequences like music or speech requires the rapid and temporally precise production of events (e.g., notes and chords), often at fast rates. Memory retrieval in these circumstances may rely on the simultaneous activation of both the current event and the surrounding context (Lashley, 1951). We describe an extension to a model of incremental retrieval in sequence production (Palmer & Pfordresher, 2003) that incorporates this logic to predict overall error rates and speed-accuracy trade-offs, as well as types of serial ordering errors. The model-assumes that retrieval of the current event is influenced by activations of surrounding events. Activations of surrounding events increase over time, such that both the accessibility of distant events and overall accuracy increases at slower production rates. The model's predictions were tested in an experiment in which pianists performed unfamiliar music at 8 different tempi. Model fits to speed-accuracy data and to serial ordering errors support model predictions. Parameter fits to individual data further suggest that working memory contributes to the retrieval of serial order and overall accuracy is influenced in addition by motor dexterity and domain-specific skill.

Covert motor activity on NoGo trials in a task sharing paradigm: evidence from the lateralized readiness potential

Previous studies on task sharing propose that a representation of the co-actor's task share is generated when two actors share a common task. An important function of co-representation seems to lie in the anticipation of others' upcoming actions, which is essential for one's own action planning, as it enables the rapid selection of an appropriate response. We utilized measures of lateralized motor activation, the lateralized readiness potential (LRP), in a task sharing paradigm to address the questions (1) whether the generation of a co-representation involves motor activity in the non-acting person when it is other agent's turn to respond, and (2) whether co-representation of the other's task share is generated from one's own egocentric perspective or from the perspective of the actor (allocentric). Results showed that although it was the other agent's turn to respond, the motor system of the non-acting person was activated prior to the other's response. Furthermore, motor activity was based on egocentric spatial properties. The findings support the tight functional coupling between one's own actions and actions produced by others, suggesting that the involvement of the motor system is crucial for social interaction.

Movement planning and reprogramming in individuals with autism

Two experiments explored how individuals with and without autism plan and reprogram movements. Participants were given partial or complete information regarding the location of the upcoming manual movement. In Experiment 1, direct information specified the hand or direction of the upcoming movement. These results replicated previous reports that participants with autism utilize advance information to prepare their movements in the same manner as their chronologically age matched peers. Experiment 2 examined how individuals respond to an unexpected change in the movement requirements. Participants received advance information about the hand and direction of the upcoming movement. On 20% of the trials participants needed to adjust either the hand or direction they had prepared. Overall, the individuals with autism had difficulty reprogramming already planned movements, particularly if a different effector was required.

Evidence for fast, low-level motor resonance to action observation: an MEG study

Lateralized magnetic fields were recorded from 12 subjects using a 151 channel magnetoencephalography (MEG) system to investigate temporal and functional properties of motor activation to the observation of goal-directed hand movements by a virtual actor. Observation of left and right hand movements generated a neuromagnetic lateralized readiness field (LRF) over contralateral motor cortex. The early onset of the LRF and the fact that the evoked component was insensitive to the correctness of the observed action suggest the operation of a fast and automatic form of motor resonance that may precede higher levels of action understanding.

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 beat goes on: rhythmic modulation of cortical potentials by imagined tapping

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180 degrees out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions.

Sensorimotor effects of pergolide, a dopamine agonist, in healthy subjects: a lateralized readiness potential study

OBJECTIVE

The major purpose of the present study was to further elucidate dopaminergic modulation of sensorimotor processing in healthy human subjects.

MATERIALS AND METHODS

To more specifically analyze dopaminergic effects on premotor and motor stages of sensorimotor processing, lateralized readiness potentials (LRPs) were obtained. In a randomized double-blind crossover design, either 0.075 mg of the D1/D2 dopamine (DA) agonist pergolide or placebo were administered to 12 healthy male volunteers ranging from 19 to 25 years in age. The subjects performed a two-choice visual reaction time task. In addition to behavioral measures, such as response speed and error rate, stimulus-locked LRP (S-LRP) and response-locked LRP (LRP-R) latencies were determined. To better dissociate potential central and peripheral motor effects, measures of response dynamics and response-locked electromyogram (EMG-R) recordings were also obtained.

OBSERVATIONS

Pergolide reliably enhanced speed of stimulus-related information processing as indicated by shorter S-LRP latencies while LRP-R latencies, reaction time, and indicators of response dynamics were not influenced by DA agonistic treatment. Furthermore, lower EMG-R amplitudes and an increased number of wrong-hand responses were observed under pergolide compared to placebo.

CONCLUSION

The results indicate that dopaminergic neurotransmission effectively modulates early perceptual and cognitive stages of information processing as suggested by neural network models of the functional role of prefrontal DA. The lack of an effect on aspects of motor processing may be due to a higher capacity of the nigrostriatal compared to the mesocortical DA system to compensate pharmacologically induced changes in dopaminergic activity.

The speed of visual attention in schizophrenia: electrophysiological and behavioral evidence

Schizophrenia is characterized by a substantial slowing of manual response times and by impairments in attention. However, prior research has not investigated whether attention itself is slowed in schizophrenia, and this was the goal of the present study. In Experiment 1, the N2pc component of the event-related potential waveform-an electrophysiological correlate of the focusing of attention-was recorded from 24 schizophrenia spectrum patients and 13 control subjects. Although behavioral response times were delayed by over 100 ms in the patient group, the onset latency of the N2pc component was virtually identical across groups, and no reduction in N2pc amplitude was observed in the patient group. In Experiment 2, a new cueing paradigm was developed to provide a behavioral measure of the speed of attention in 22 schizophrenia spectrum patients and 13 control subjects. We found that the average time required to allocate attention to a cued location was only 19 ms greater for the patient group than for the control group, with most patients within the range of the control subjects. Together, these experiments revealed little or no slowing of the allocation of visual-spatial attention in patients with schizophrenia. Thus, the mechanisms responsible for allocating attention to salient visual targets appear to be largely unaffected by the illness, and the well documented slowing of manual response times in schizophrenia cannot easily be explained by a slowing of attention.

Different effects of exogenous cues in a visual detection and discrimination task: delayed attention withdrawal and/or speeded motor inhibition?

Several studies examining spatial attention have found a discrepancy regarding the effects of exogenous cues on reaction times in visual detection and discrimination tasks. Namely, across a wide range of cue-target intervals, responses are slower for targets at cued than at uncued locations (inhibition of return) in detection tasks, whereas responses are faster for targets at cued than at uncued locations (facilitation) in discrimination tasks. Two hypotheses were proposed to account for this discrepancy. First, attention may dwell much longer on the exogenously cued location in discrimination tasks because stimuli have to be identified (i.e., the delayed attention withdrawal hypothesis). Secondly, due to increased motor preparation in detection tasks, cue-induced motor inhibition may rise much faster in these tasks than in discrimination tasks (i.e., the speeded motor inhibition hypothesis). We examined to what extent these hypotheses can account for effects of exogenous cues in a detection and discrimination task on the extrastriate P1 component, and the onset of motor activation, as indexed by the lateralized readiness potential. Some support was found for the delayed attention withdrawal hypothesis, as task-dependent cueing effects were found on the P1 component. Other aspects of our data, however, indicate that motor inhibition is also involved. Based on these findings, we propose that effects of exogenous cues in detection and discrimination tasks are determined by the interplay between two mechanisms, of which the time courses of activation may be modulated by the specific setting.

Function of striatum beyond inhibition and execution of motor responses

We used functional magnetic resonance imaging (fMRI) to study the role of the striatum in inhibitory motor control. Subjects had to refrain from responding to designated items (STOP trials) within a similar series of motor stimuli. Striatal activation was increased significantly compared to that when responding to all targets within a series of motor stimuli, indicating that the striatum is more active when inhibitory motor control over responses is required. The likelihood of a STOP trial was varied parametrically by varying the number of GO trials before a STOP trial. We could thus measure the effect of expecting a STOP trial on the fMRI response in the striatum. We show for the first time in humans that the striatum becomes more active when the likelihood of inhibiting a planned motor response increases. Our findings suggest that the striatum is critically involved in inhibitory motor control, most likely by controlling the execution of planned motor responses.

Lateralization of event-related beta desynchronization in the EEG during pre-cued reaction time tasks

OBJECTIVE

Here, we investigate whether the event-related desynchronization (ERD) of spectral components of the cortical EEG in the beta (13-30 Hz) frequency range may, in part, index motor selection processes. Specifically, we sought evidence for a contralaterally dominant component of the beta ERD that is limited to trials in which motor selection is possible prior to any imperative cue to move, with attendant behavioural advantage.

METHODS

We measured reaction time and assessed the lateralization of beta ERD in 12 healthy volunteers as they performed pre-cued choice reaction time tasks, in which warning S1 cues were either fully predictive about the laterality of a subsequent imperative S2 signal or provided no laterality information. We calculated 'lateralized ERD index' (LERDI), a parallel measure to the lateralized readiness potential in the time domain.

RESULTS

Trials with 100% S1-S2 congruency produced significantly shorter reaction times than trials with 50% S1-S2 congruency, where laterality information was unreliable. Beta LERDI indicated significantly greater lateralisation of the ERD in the warning-go interval and of event-related synchronization (ERS) following movement in the 100% condition than in the 50% condition. The lateralization of the beta ERD with respect to hand persisted, even when subjects were instructed to make movements of opposite laterality to those prompted.

CONCLUSIONS

Lateralized EEG changes occur in the beta band in the S1-S2 interval prior to movement, but only when informative warning cues allow early motor selection, as suggested by the shortening of reaction time. Furthermore, the enhanced contralateral ERS with 100% S1-S2 congruency suggests that this phenomenon is at least partly independent of afferent feedback, as the same movement was made in the 100 and 50% conditions.

SIGNIFICANCE

Lateralized suppression of beta power prior to externally generated movements is associated with motor selection.

Preparing for Action: Inferences from CNV and LRP

Abstract The execution of efficient motor actions is often preceded by preparation in the central nervous system. Although this kind of preparation cannot be observed directly, it, nevertheless, shortens reaction time. In this review we focus on two types of action preparation, namely event and temporal preparation. In particular, we show how modern event-related brain potential techniques can be employed to determine both the covert processes underlying such preparatory effects as well as their locus within the processing chain between stimulus input and action output.