Brain dynamics in alpha and beta frequencies underlies response activation during readiness of goal-directed hand movement.

How the brain generates response readiness and preparation for hand movements is not yet understood. We hypothesised that coupled interactions in alpha and beta frequencies become modulated in central-motor brain areas during response readiness. Phase synchronization in alpha (~9-11 Hz) and beta (~18-22 Hz) frequencies was analysed prior to a finger response in people with normal lateralised readiness potentials (LRP). Specifically, Phase Locking Values (PLV) and source topographies were assessed in EEG data with Go-NoGo tasks in 18 healthy participants. Analyses involving alpha and beta phase-coupled activity in electrodes overlying central-motor brain regions and from adjacent frontal sites were compared to address the hypothesised specificity of motor area modulations as underlying response readiness. Control analyses using alpha-beta phase-coupling with the alpha at electrodes overlying occipital areas were included. Results revealed smaller PLVs in the alpha-beta phase interactions using alpha from C3, Cz, C4 electrodes compared with alpha from F3, Fz, F4, thereby isolating motor regions specifically. Analyses of the source topography of synchronous beta signals (coupled with central-motor alpha) revealed parietal, occipital and right frontal areas, possibly implicating a role of motor and visual attention, movement intention in the time window of the LRP. In sum, we isolated central-motor interactions involving centrally located alpha, coupled with parietal, occipital, and frontal beta activity in association with processes of movement readiness.

The Brain's Reward Response Occurs Even Without Actual Reward!

What if the brain's response to reward occurs even when there is no reward? Wouldn't that be a further concern for people prone to problem gambling and other forms of addiction, like those related to eating? Electroencephalography was employed to investigate this possibility using probabilistic feedback manipulations and measures of known event-related potentials (ERPs) related to reward processing. We tested the hypothesis-that reward-based ERPs would occur even in the absence of a tangible reward and when manipulations on expectation are implicit. The well-known P300 response potential was a key focus, and was assessed in non-gambling volunteer undergraduates on a task involving experimentally-manipulated probabilities of positive or negative feedback comprising three trial types-80, 50, or 20% positive feedback. A feedback stimulus (F1) followed a guess response between two possible outcomes (implicit win/loss), and then a second feedback stimulus (F2) was presented to confirm an alleged 'win' or 'loss' (explicit win/loss). Results revealed that amplitude of the P300 in F1-locked data (implicit manipulation) was larger (more positive) on average for feedback outcomes that were manipulated to be less likely than expected. The effect is pronounced after increased time on task (later trials), even though the majority of participants were not explicitly aware of our probability manipulations. For the explicit effects in F2-locked data, no meaningful or significant effects were observed. These findings point to the existence of proposed success-response mechanisms that operate not only explicitly but also with implicit manipulations that do not involve any direct indication of a win or loss, and are not associated with tangible rewards. Thus, there seems to be a non-explicit form of perception (we call 'implicit') associated with an internal experience of wins/losses (in the absence of actual rewards or losses) that can be measured in associated brain processes. The potential significance of these findings is discussed in terms of implications for problem gambling.

Pre-movement planning processes in people with congenital mirror movements.

OBJECTIVE: Pre-movement processes were investigated in people with Congenital mirrormovement (CMM), a rare disorder in which bilateral movement (mirroring) occurs in the upper distal extremities (primarily the hands and fingers) during intended unilateral movements. Abnormal density of ipsilateral corticospinal projections is an established hallmark of CMM. This study tested whether the Lateralised Readiness Potential (LRP), which reflects movement planning and readiness, is also abnormal in people with CMM. METHODS: Twenty-eight neurologically-normal controls and 8 people with CMM were tested on a unimanual Go/No-go task while electroencephalography (EEG) was recorded to assess the LRP. RESULTS: No significant group differences were found in reaction time (RT). However, significantly smaller LRP amplitudes were found, on average, in the CMM group compared to Controls at central-motor (C3,C4) sites in stimulus-locked and response-locked epochs; similar group differences were also found at further frontal sites (F3,F4) during response-locked epochs. CONCLUSIONS: Abnormal brain activity in pre-movement processes associated with response planning and preparation is present in people with CMM. SIGNIFICANCE: Aberrant bilateral activity during pre-movement processes is clearly implicated; whether part of the etiology of CMM, or as a mechanism of neuro-compensation, is not yet known.

A novel role for the DNA repair gene Rad51 in Netrin-1 signalling.

Mutations in RAD51 have recently been linked to human Congenital Mirror Movements (CMM), a developmental disorder of the motor system. The only gene previously linked to CMM encodes the Netrin-1 receptor DCC, which is important for formation of corticospinal and callosal axon tracts. Thus, we hypothesised that Rad51 has a novel role in Netrin-1-mediated axon development. In mouse primary motor cortex neurons, Rad51 protein was redistributed distally down the axon in response to Netrin-1, further suggesting a functional link between the two. We next manipulated Rad51 expression, and assessed Netrin-1 responsiveness. Rad51 siRNA knockdown exaggerated Netrin-1-mediated neurite branching and filopodia formation. RAD51 overexpression inhibited these responses, whereas overexpression of the CMM-linked R250Q mutation, a predicted loss-of-function, had no effect. Thus, Rad51 appears to negatively regulate Netrin-1 signalling. Finally, we examined whether Rad51 might operate by modulating the expression of the Unc5 family, known negative regulators of Netrin-1-responsiveness. Unc5b and Unc5c transcripts were downregulated in response to Rad51 knockdown, and upregulated with RAD51 overexpression, but not R250Q. Thus, Rad51 negatively regulates Netrin-1 signalling, at least in part, by modulating the expression of Unc5s. Imbalance of positive and negative influences is likely to lead to aberrant motor system development resulting in CMMs.

The allocation of attention to learning of goal-directed actions: a cognitive neuroscience framework focusing on the Basal Ganglia.

The present paper builds on the idea that attention is largely in service of our actions. A framework and model which captures the allocation of attention for learning of goal-directed actions is proposed and developed. This framework highlights an evolutionary model based on the notion that rudimentary functions of the basal ganglia have become embedded into increasingly higher levels of networks which all contribute to adaptive learning. Supporting the proposed model, background literature is presented alongside key evidence based on experimental studies in the so-called "split-brain" (surgically divided cerebral hemispheres), and selected evidence from related areas of research. Although overlap with other existing findings and models is acknowledged, the proposed framework is an original synthesis of cognitive experimental findings with supporting evidence of a neural system and a carefully formulated model of attention. It is the hope that this new synthesis will be informative in fields of cognition and other fields of brain sciences and will lead to new avenues for experimentation across domains.

Reliability and diagnostic characteristics of clinical tests of upper limb motor function.

There is a paucity of information on the inter-rater reliability and predictive value of components of the neurological examination. Selected tests of upper limb motor function were studied in 34 patients with Parkinson's disease, upper motor neuron disease or cerebellar disease and in 25 control participants. Video recordings were independently evaluated and scored by two clinicians to determine inter-rater reliability (kappa) and predictive values. Kappa values ranged from 0.00 to 0.73. Highest positive predictive values (PPV) were obtained for the Barré test, arm raise, forearm rolling and finger nose tests. Negative predictive values (NPV) were mostly low, with highest values for unimanual sequential finger tap and rhythmic tap. The combined tests had PPV of 0.58 and NPV of 0.73. This study demonstrates that these clinical tests have poor inter-rater reliability and low negative predictive value when used in isolation.

Concussion causes transient dysfunction in cortical inhibitory networks but not the corpus callosum.

The corpus callosum (CC) is thought to be especially vulnerable in traumatic brain injury. Bimanual cost (a slowing of reaction time with bimanual compared to unimanual responses) is a sensitive indicator of CC function. To determine whether CC dysfunction is a significant feature of mild traumatic brain injury, unimanual and bimanual reaction times were studied in 10 recently concussed patients and 10 healthy participants. Reaction times were studied within 1 week of concussion and again after 1 month. Concussion symptoms were assessed with the Rivermead Postconcussion Symptoms Questionnaire. The bimanual cost was present at both testing sessions in patients and healthy controls. Although overall reaction times were slower in concussed patients during session 1, these had improved by session 2, as did the symptom scores. These findings suggest that the pathogenesis of mild traumatic brain injury involves intrahemispheric cortical networks rather than impaired interhemispheric communication via the CC.

Experience-dependent effects in unimanual and bimanual reaction time tasks in musicians.

Engaging in musical training has been shown to result in long-term cognitive benefits. The authors examined whether basic cognitive-motor processes differ in people with extensive musical training and in nonmusicians. Musicians (n = 20) and nonmusicians (n = 20) performed a simple reaction time (RT) task under unimanual and bimanual conditions. Musicians' RTs were faster overall than were those of nonmusicians, and those who began their musical training at an earlier age (around age 7-8 years, on average) exhibited a larger bimanual cost than did those who began later (around 12 years, on average). The authors conclude that experience-dependent changes associated with musical training can result in greater efficacy of interhemispheric connections if those changes occur during certain critical periods of brain development.

Bimanual gestures: expressions of spatial representations that accompany speech processes.

The present study investigated a possible relationship between gestures and spatial processes underlying speech, with a focus on both unimanual and bimanual gestures. The amount, form, and type of gestures accompanying spontaneous verbal responses were quantified in five conditions that manipulated the degree to which the verbal description required spatial elaboration. Two conditions that required spatial elaboration included describing one's present house or lounge. To assess gestures accompanying temporally ordered events, a third condition required description of one's daily routine. The two remaining conditions assessed time periods associated with the past (describe the house you lived in as a child) and future (describe the house you would like to live in 15-20 years from now). Higher levels of gesture were found in spatial conditions compared to the temporally ordered routine condition for bimanual gestures, and the reverse was found for unimanual gestures. These results are described in terms of a hypothesised link between bimanual gestures and spatial cognition.

Dissociation of bimanual responses with the Simon effect: on the nonunitization of bimanual responses.

The authors examined whether responses of the 2 hands were completely unitized when participants (N=36) produced bimanual responses to lateralized targets in a Simon-type paradigm. Their primary aim was to investigate whether lateralized stimuli differentially influence the response dynamics of the 2 hands. Simon effects were obtained in reaction time and force components of the bimanual response by the hand on the same side as the lateralized stimulus were more forceful than were those of the other hand. Also, Simon effects were larger when the lateralized target appeared alone than when it was accompanied by a distractor on the other side of the display. Finally, responses of the 2 hands were correlated most strongly when stimulus displays were symmetrical. The authors conclude that bimanual responses are strongly coupled, but not perfectly so.

Spatial conceptual influences on the coordination of bimanual actions: when a dual task becomes a single task.

When the left and right hands produce 2 different rhythms simultaneously, coordination of the hands is difficult unless the rhythms can be integrated into a unified temporal pattern. In the present study, the authors investigated whether a similar account can be applied to the spatial domain. Participants (N = 8) produced a movement trajectory of semicircular form in single-limb and bimanual conditions. In the bimanual tasks, 1 limb moved above the other in the frontal plane. Bimanual unified tasks were constructed so that the spatial paths to be produced by the 2 limbs could be easily conceptualized as parts of a unified circle pattern. Bimanual distinct tasks availed a less obvious spatial pattern that would unify the 2 tasks, despite similar demands placed on the coordination dynamics in the 2 cases (e.g., the phase relations). The authors conclude that a dual task becomes a single task, and interlimb interference is reduced, when the spatial patterns produced by the 2 hands form a geometric arrangement that can be conceptualized as a unified representation.

The effect of callosotomy on novel versus familiar bimanual actions: a neural dissociation between controlled and automatic processes?

The corpus collosum is the large band of fibers that connects the two cerebral hemispheres of the brain. Individuals who have had the fibers of these tracts surgically severed by callosotomy are able to draw two different spatial figures simultaneously using the left and right hands, without evidence of interactions in the spatial planning processes. Paradoxically, tasks (e.g., tying shoes) that appear to depend on spatial interactions between the left and right hands, each of which is controlled by a separate cerebral hemisphere, pose little difficulty. How can this be? In the study reported here, we observed that well-learned cooperative actions of the hands remain intact in 2 callosotomy patients, whereas actions novel to these patients are virtually impossible for them to produce without visual guidance. We infer that duplicate memory engrams of well-learned actions can be accessed by both cerebral hemispheres without callosal mediation, whereas callosal interactions are necessary for precise cross-matching of sensory information during spatial planning or perceptual-motor learning.

The psychological refractory period effect following callosotomy: uncoupling of lateralized response codes.

A callosotomy patient was tested in 2 dual-task experiments requiring successive speeded responses to lateralized stimuli. The patient showed a robust psychological refractory period (PRP) effect. Three aspects of the data indicate that, unlike for the control participants, the PRP effect for the split-brain patient should not be attributed to a response selection bottleneck. First, the patient did not show an increase in reaction time (RT) when the 2 tasks required responses from a common output system compared with when different output systems were used. Second, inconsistent stimulus-response mappings for the 2 tasks increased RTs for the control participants but had minimal effect on the performance of the split-brain patient. Third, the consistency manipulation was underadditive with stimulus onset asynchrony but was additive or overadditive for the normal participants. These results suggest that the persistent PRP effect following callosotomy should be attributed to a bottleneck associated with response initiation, a strategy adopted to comply with the task demands, or a combination of these factors.

Spatial coupling in the coordination of complex actions.

The majority of investigations on coordinated action have focused on temporal constraints in movements. Recent studies have demonstrated spatial constraints when the hands produce different trajectory shapes simultaneously. The focus of the current study was to determine whether spatial coupling occurs in individual parameters of the actions, or whether the shapes per se undergo accommodation. Subjects were tested on a bimanual paradigm to investigate the nature of spatial constraints in complex tasks. Shape and size of the required trajectories were varied for two limbs. When trajectories that require different shapes were assigned to the two hands, disruption in the spatial characteristics of the trajectories was observed. Disruption in the global patterns of the trajectories could be described on the basis of coupling in individual parameters of action, direction, and amplitude, which could be inferred by decomposing the trajectories into orthogonal components. Amplitude accommodation in these orthogonal components of motion increased linearly with the difference in required amplitude for the two limbs. Interpretations of these effects suggest that directional coupling is a result of interference between two different response plans, whereas amplitude coupling may be related to either planning or execution variables. These results strongly suggest the need for further investigation of the spatial domain of complex coordinated action.

Differences in bimanual coordination associated with stuttering.

The motor coordination of adults who stutter was examined in the performance of a bimanual movement task. Fifteen subjects who stutter and 15 matched subjects who do not stutter performed three trials of a bimanual finger movement task. Subjects were required to produce a flexion and extension movement of the metacarpophalangeal joint of each index finger in rhythm to a metronome. The rate of movement increased during the 70 s trial. Stutterers could maintain movements at the prescribed rate as well as nonstutterers; however, stutterers moved with less amplitude and peak velocity. In addition, dynamical analysis revealed that subjects who stutter exhibited greater relative phase variability than subjects who do not stutter. These results shed new light on the mixed results of earlier studies on nonspeech motor performance of individuals who stutter and suggest that there are strategic differences as well as coordination differences that should be observable across a variety on motor tasks requiring coordination of multiple effectors.

Reduced Timing Variability in Patients with Unilateral Cerebellar Lesions during Bimanual Movements.

Timing variability on a repetitive tapping task was studied in subjects with unilateral cerebellar lesions. During unimanual tapping, within-hand variability was larger when tapping with the ipsilesional hand in comparison to tapping with the contralesional hand. However, variability in the impaired hand was greatly reduced when subjects tapped with two hands together. The improvement in within-hand variability during bimanual tapping was associated with a reduction in central variability rather than response implementation variability according to the two-process model of Wing and Kristofferson (1973). It is proposed that (1) each half of the cerebellum independently regulates the temporal aspects of movements on the ipsilateral side and (2) temporal coupling constraints require these separate signals to be integrated prior to response implementation for bimanual movements.

Motor Performance of Stutterers and Nonstutterers on Timing and Force Control Tasks.

Recently it has been suggested that speech and manual timing tasks share a common central process (Franz, Zelaznik, & Smith, 1992): Because stuttering is thought to be related to deficits in motoric processes such as timing, stutterers (n = 15) were compared with a set of age-, education-, and sex-matched nonstutterers on timing and isometric force-production tasks. In the timing tasks, subjects flexed and extended the right index finger at the metacarpophalangeal joint at cycle durations of 600, 500, 400, 300, and 200 ms. In the force-production tasks, subjects generated isometric forces to match target force levels displayed on a cathode-ray tube (CRT) screen. There were five levels of force, ranging from.11 to 7.85 newtons. Overall, there were no differences in timing and force-production performance between stutterers and nonstutterers. These results are similar to those obtained recently by Hulstijn, Summers, van Lieshout, and Peters (1992). We suggest that stuttering is not characterized by a general deficit in rhythmic timing. Instead, the motor deficit associated with stuttering should be viewed as speech specific.