Learning and altering behaviours by reinforcement: neurocognitive differences between children and adults.

This study examined neurocognitive differences between children and adults in the ability to learn and adapt simple stimulus-response associations through feedback. Fourteen typically developing children (mean age=10.2) and 15 healthy adults (mean age=25.5) completed a simple task in which they learned to associate visually presented stimuli with manual responses based on performance feedback (acquisition phase), and then reversed and re-learned those associations following an unexpected change in reinforcement contingencies (reversal phase). Electrophysiological activity was recorded throughout task performance. We found no group differences in learning-related changes in performance (reaction time, accuracy) or in the amplitude of event-related potentials (ERPs) associated with stimulus processing (P3 ERP) or feedback processing (feedback-related negativity; FRN) during the acquisition phase. However, children's performance was significantly more disrupted by the reversal than adults and FRN amplitudes were significantly modulated by the reversal phase in children but not adults. These findings indicate that children have specific difficulties with reinforcement learning when acquired behaviours must be altered. This may be caused by the added demands on immature executive functioning, specifically response monitoring, created by the requirement to reverse the associations, or a developmental difference in the way in which children and adults approach reinforcement learning.

'Everybody just thinks I'm weird': a qualitative exploration of the psychosocial experiences of adolescents with Tourette syndrome.

BACKGROUND: Research suggests Tourette syndrome (TS) can have a negative impact on quality of life. To date, little research has examined the perspectives of young people with this condition in depth. METHODS: Six 14- to 16-year-olds with TS took part in semi-structured interviews to explore the perceived impact of this condition on self and on relationships with others. The transcripts were analysed using interpretative phenomenological analysis. RESULTS: The young people felt that TS was a constant presence in their lives, but one they have learnt to cope with well. Most had developed supportive friendships but encountered problems when interacting with the wider peer network. Specific concerns around meeting new people and future employment were voiced. CONCLUSIONS: The adolescents described specific ways in which TS affects quality of life and social interactions, and the effort it can take to cope effectively with this condition.

Inefficient cerebral recruitment as a vulnerability marker for schizophrenia.

BACKGROUND: Patients with schizophrenia and their first-degree relatives exhibit both abnormally diminished and increased neural activation during cognitive tasks. In particular, excessive task-related activity is often observed when tasks are easy, suggesting that inefficient cerebral recruitment may be a marker of vulnerability for schizophrenia. This hypothesis might best be tested using a very easy task, thus avoiding confounding by individual differences in task difficulty. METHOD: Eighteen people with schizophrenia, 18 unaffected full siblings of patients with schizophrenia and 26 healthy controls performed an easy auditory target-detection task in a 3-T magnetic resonance imaging (MRI) scanner. Groups were matched for accuracy on the task. Blood oxygen level-dependent (BOLD) responses to non-target stimuli in participants with vulnerability for schizophrenia (siblings and patients) were compared with those of healthy controls, and those of patients with those of unaffected siblings. BOLD responses to targets were compared with baseline, across groups. RESULTS: Subjects with vulnerability for schizophrenia showed significant hyperactivation to non-targets in brain areas activated by targets in all groups, in addition to reduced deactivation to non-targets in areas suppressed by targets in all groups. Siblings showed greater activation than patients to non-targets in the medial frontal cortex. Patients exhibited significantly longer reaction times (RTs) than unaffected siblings and healthy controls. CONCLUSIONS: Inefficient cerebral recruitment is a vulnerability marker for schizophrenia, marked by reduced suppression of brain areas normally deactivated in response to task stimuli, and increased activation of areas normally activated in response to task stimuli. Moreover, siblings show additional activation in the medial frontal cortex that may be protective.

ERP indices of persisting and current inhibitory control: a study of saccadic task switching.

Previous studies have found that inhibition of a biologically dominant prepotent response tendency is required during the execution of a less familiar, non-prepotent response. However, the lasting impact of this inhibition and the cognitive mechanisms to flexibly switch between prepotent and non-prepotent responses are poorly understood. We examined the neurophysiological (ERP) correlates of switching between prosaccade and antisaccade responses in 22 healthy volunteers. The behavioural data showed significant switch costs in terms of response latency for the prosaccade task only. These costs occurred exclusively in trials when preparation for the switch was limited to 300 ms, suggesting that inhibition of the prepotent prosaccade task either passively dissipated or was actively overcome during the longer 1000 ms preparation interval. In the neurophysiological data, a late frontal negativity (LFN) was visible during preparation for a switch to the prosaccade task that was absent when switching to the antisaccade task, which may reflect the overcoming of persisting inhibition. During task implementation both saccade types were associated with a late parietal positivity (LPP) for switch relative to repetition trials, possibly indicating attentional reorienting to the switched-to task, and visible only with short preparation intervals. When the prosaccade and antisaccade task were contrasted directly during task implementation, the antisaccade task exhibited increased stimulus-locked N2 and decreased P3 amplitudes indicative of active inhibition. The present findings indicate that neurophysiological markers of persisting and current inhibition can be revealed using a prosaccade/antisaccade-switching task.

The role of spatial information in advance task-set control: an event-related potential study.

Task-switching has proved to be a fruitful paradigm for studying cognitive control mechanisms. Interestingly, this avenue of study has revealed that subjects are, to some degree, able to bring about a change in task-set prior to the performance of that task (provided that they are given advance warning of the upcoming task, for instance in the form of a cue). Event-related potentials (ERPs) have proved to be a good way of measuring these rapid anticipatory control processes. To explore these processes further, the current study examined the relationship between the availability of spatial information and cue-locked task-switching ERP effects. Two groups of subjects were compared: one group could separate the task-sets on the basis of the targets' colour (the 'colour' group), the second on the basis of the targets' location (the 'spatial' group). The performance of both groups benefited to the same extent from advance cueing of task-transitions (switches or repeats), yet the ERP data revealed cue-locked (but not target-locked) differences between the two groups. The most striking of these differences was the absence of both a late positivity over posterior scalp and a late negativity over frontal scalp when the spatial group switched between tasks. Thus, it seems unlikely that these effects index stimulus-response 'reconfiguration'per se--as the mappings were identical for both groups of subjects--but rather that these task-switching processes are sensitive to how the mappings are represented.

Fractionating the cognitive control required to bring about a change in task: a dense-sensor event-related potential study.

The ability to change our behavior is one that we frequently exert, although determining the mechanisms by which we do so is far from trivial. Task switching is a useful experimental paradigm for studying cognitive control functions. Switching between tasks is associated with a decrement in performance, or "switch-cost," relative to repeating the same task. We have previously demonstrated that this cost is dependent on switching from performing one task to performing another; changing only our intended performance does not elicit the same performance deficit. Using event-related potentials (ERPs), we dissociated two electrophysiological indices mirroring this behavioral distinction [Astle, D. E., Jackson, G. M., & Swainson, R. Dissociating neural indices of dynamic cognitive control in advance task-set preparation: An ERP study of task switching. Brain Res, 1125, 94-103, 2006]. However, what was unclear were the specific aspects of performance that were critical for triggering the neural mechanisms associated specifically with switching from a previously performed task. Two candidate aspects were: (i) that performance required a physical response and (ii) that the two tasks shared their responses (they had bivalent response mappings). The present study therefore compared three separate groups to explore the effects of these different aspects of performance. Each group completed the same basic task-switching paradigm, but with either an overt response or covert response, and either switching between tasks that shared their responses (bivalent response mappings) or had separate responses (univalent response mappings). When comparing precue-locked ERPs, we observed three separable components: one common to all three groups, one which primarily dissociated overt from covert responding, and one which primarily dissociated bivalent from univalent responding. We therefore concluded that changing our behavior engages at least three dissociable mechanisms. Interestingly, in the overt conditions, residual switch-costs were absent; in addition, therefore, we concluded that it is possible to engage cognitive control in advance, such that the new behavior is as efficient as were the subject to have repeated the old behavior.

Cognitive deficits in early-onset schizophrenia spectrum patients and their non-psychotic siblings: a comparison with ADHD.

BACKGROUND: Previous research has shown cognitive deficits in patients with schizophrenia spectrum disorders in the areas of executive function, verbal memory and attention. Subtle deficits have been shown in healthy first-degree relatives of patients, suggesting that they may be trait markers. The specificity of these markers for schizophrenia compared with another neurodevelopmental disorder, Attention Deficit Hyperactivity Disorder (ADHD) has not been reliably established. METHODS: The Rey Auditory Verbal Learning Test (RAVLT), Hayling Sentence Completion Test (HSCT), FAS Test of orthographic verbal fluency (FAS) and Continuous Performance Test-Identical Pairs (CPT-IP) were administered to adolescent schizophrenia spectrum patients (SZ; n=30), adolescent siblings of schizophrenia spectrum patients (SZ-SIB; n=36), healthy control participants (HC; n=72); a neurodevelopmental comparison group of adolescents with ADHD (n=27). RESULTS: The SZ group were impaired on all measures. The SZ-SIB group were impaired on IQ, immediate recall (RAVLT), target sensitivity (CPT-IP), response initiation (HSCT); error rates for the FAS and HSCT. There were no significant differences between the SZ-SIB and ADHD groups on individual measures of cognitive function. Principal Components Analysis revealed four factors on which further analyses were conducted. The SZ-SIB and ADHD groups showed different profiles of impairment on components related to response initiation and sustained attention/vigilance when each was compared with the HC group. CONCLUSIONS: Deficits in intellectual function, verbal memory and response initiation/inhibition were found in the SZ-SIB group indicating that these are markers of risk for schizophrenia. Subtle differences in profiles of impairment in the SZ-SIB and ADHD groups on composite measures of attention and response initiation require further investigation.

Enhanced cognitive control in Tourette Syndrome during task uncertainty.

Tourette Syndrome (TS) is a developmental neurological condition that is characterised by the presence of multiple motor and one or more vocal tics. Tics are highly stereotyped repetitive behaviours that fluctuate in type, complexity and severity. TS has been linked to impaired cognitive control processes, however, a recent study (Mueller et al. in Curr Biol 16:570-573, 2006) demonstrated that young people with TS, although exhibiting chronic motor and vocal tics, nevertheless performed significantly better than a group of age-matched controls on a task that required extremely high levels of cognitive control (i.e., predictably shifting between executing pro-saccade and anti-saccade responses to a visual stimulus). As predictable task sequences allow task-related cognitive processes to commence prior to the presentation of target stimuli we examined whether the superior performance of the TS group could be replicated when task sequences were varied unpredictably. Our results confirmed that both the TS group and an age-matched control group benefited, by the same extent, when the saccade task (pro-saccade vs. anti-saccade) was pre-cued. In contrast, while the control group showed a significant decrease in performance on task switch trials relative to task repetition trials-the TS group exhibited no significant 'costs' of switching task. While task performance was modulated by response and target location shifts in the control group, these factors had less impact on the TS group's performance on task switch trials. These results confirm and extend the previous demonstration that individuals with TS exhibit paradoxically greater levels of cognitive control than healthy controls.

Behavioural and neurophysiological correlates of bivalent and univalent responses during task switching.

A hallmark of human behaviour is its flexibility. In any given circumstance there is typically a range of possible responses that could be selected. In the current study participants were presented with stimulus displays that afforded two simple cognitive tasks and were required to switch predictably between them. The judgements for each task were either uniquely mapped onto separate effectors (univalent conditions) or else mapped onto shared effectors (bivalent condition). The results demonstrated that whilst behavioural switch costs were similar across the mapping conditions, these conditions differed in the patterns of brain activity observed during task preparation and early visual processing of the target. Specifically, a cue-locked switch-related late frontal negativity was present over frontal sensors for the bivalent condition only, and a target-locked N1 over occipital sensors was larger in the bivalent condition than the univalent conditions. In contrast, a switch-related target-locked P3b component was common to all mapping conditions. These findings are discussed with respect to differences in processing demands for switching between tasks with bivalent versus univalent responses.

Dissociating neural indices of dynamic cognitive control in advance task-set preparation: an ERP study of task switching.

Switching between different tasks is associated with performance deficits, or 'switch costs', relative to repeating the same task. Recent evidence suggests that response rather than task selection processes may be a major cause of switch costs [Schuch, S., Koch, I., 2003. The role of response selection for inhibition of task sets in task shifting. J Exp Psychol Hum Percept Perform, 29 (1) 92-105]. Thus, switch costs are not incurred if on the preceding trial a task has been prepared for but no response required (a 'no-go' trial). We investigated the relationship between response selection and the subsequent preparation of an alternative task set. While switch costs were absent following 'no-go' trials, ERP differences during the precueing interval showed that response selection has implications for subsequent task preparation as well as for task performance per se. The results are discussed in relation to the dissociation of intention versus action in behavioural control and the role of inhibition in switching between task sets.

Using advance information in dynamic cognitive control: an ERP study of task-switching.

Ensuring that behavior remains appropriate over time requires dynamic, flexible control. We used the task-switching procedure to investigate the mechanisms whereby advance information is used to control behavior under conditions of frequently changing task-rules. The color of target stimuli signaled which task-set (or behavioral 'rule') was required on each trial. We provided different forms of advance information in two conditions and found a double dissociation in their effects: visual precues ('precueing') facilitated task-switching, whereas a fixed task-sequence ('predictability') facilitated task-repetition. In addition, precueing was associated with a late parietal positive ERP which preceded target onset, whereas predictability produced an increase in the target-locked centro-parietal P3b ERP. We suggest that these results indicate the activity of two distinct mechanisms. The first, driven by a task-cue and indexed by the late parietal positivity, may drive efficient task-performance on precued switch trials but occurs too late on non-precued switch trials to index an anticipatory task-set reconfiguration process. The second may constitute active consolidation or maintenance of a particular task-set which occurs at least one trial ahead, when task-repetitions are predictable, and results in facilitation of target stimulus evaluation.

ERP correlates of a receptive language-switching task.

Previous research has shown large response time costs (in excess of 50 ms) when bilingual speakers switch predictably back and forth between naming items (a productive switching task) in their first (L1) and second languages (L2). A recent study using event-related potentials (ERPs) has shown that switching between languages is associated with activity over frontal (N2) and parietal (late positive complex) areas of cortex (Jackson, Swainson, Cunnington, & Jackson, 2001). Switching between naming in different languages requires a switch in both language representations and language-specific motor responses. The current study investigated a receptive (input) language-switching task with a common manual response. Number words were presented in L1 and L2, and participants were required to judge whether the words were odd or even (a parity judgement). Response costs were considerably reduced, and the frontal and parietal switch related activity reported in the productive switching task was absent. Receptive switching was associated with early switch-related activity over central sensors that were not language specific. These results are discussed in relation to the idea that there is no language-specific lexical selection mechanism. Instead the costs of receptive language switching may arise from outside the bilingual lexicon.

Cognitive control mechanisms revealed by ERP and fMRI: evidence from repeated task-switching.

We investigated the extent to which a common neural mechanism is involved in task set-switching and response withholding, factors that are frequently confounded in task-switching and go/no-go paradigms. Subjects' brain activity was measured using event-related electrical potentials (ERPs) and event-related functional MRI (fMRI) neuroimaging in separate studies using the same cognitive paradigm. Subjects made compatible left/right keypress responses to left/right arrow stimuli of 1000 msec duration; they switched every two trials between responding at stimulus onset (GO task-green arrows) and stimulus offset (WAIT task-red arrows). With-holding an immediate response (WAIT vs. GO) elicited an enhancement of the frontal N2 ERP and lateral PFC activation of the right hemisphere, both previously associated with the "no-go" response, but only on switch trials. Task-switching (switch vs. nonswitch) was associated with frontal N2 amplification and right hemisphere ventrolateral PFC activation, but only for the WAIT task. The anterior cingulate cortex (ACC) was the only brain region to be activated for both types of task switch, but this activation was located more rostrally for the WAIT than for the GO switch trials. We conclude that the frontal N2 ERP and lateral PFC activation are not markers for withholding an immediate response or switching tasks per se, but are associated with switching into a response-suppression mode. Different regions within the ACC may be involved in two processes integral to task-switching: processing response conflict (rostral ACC) and overcoming prior response suppression (caudal ACC).

Functional coupling between the limbs during bimanual reach-to-grasp movements.

While it is frequently advantageous to be able to use our hands independently, many actions demand that we use our hands co-operatively. In this paper we present two experiments that examine functional binding between the limbs during the execution of bimanual reach-to-grasp movements. The first experiment examines the effect of gaze direction on unimanual and bimanual reaches. Even when subjects' eye movements are restricted during bimanual reaches so that they may only foveate one target object, the limbs remain tightly synchronized to a common movement duration. In contrast, grip aperture is independently scaled to the size of the target for each hand. The second experiment demonstrates however, that the independent scaling of grip aperture is task dependent. If the two target objects are unified so that they appear to be part of a single object, grip apertures become more similar across the hands (i.e., grip aperture to the large target object is reduced in size while peak aperture to the small target item is increased in size). These results suggest that the coupling of the limbs can operate at a functional level.

Co-ordination of bimanual movements in a centrally deafferented patient executing open loop reach-to-grasp movements.

Many everyday tasks require that we use our hands co-operatively. For tasks where both hands are required to perform the same action, a common motor program can be used. But, where each hand must perform a different action, some degree of independent control of each hand is required. In this paper we examine the co-ordination of bimanual movement kinematics in a female patient recovering from brain injury involving anterior regions of the parietal lobe of the right hemisphere, which has resulted in a dense hemianaesthesia of her left arm. A particular focus of this paper is the co-ordination of bimanual movements for reaches executed without visual feedback. Specifically we present new data, which quantify the synchronisation of patient D.B.'s hands by comparing their relative time lag at the start and the end of her bimanual reaches. The results are discussed with particular reference to the role played by limb proprioception in the planning and control of prehension movements.

The control of bimanual reach-to-grasp movements in hemiparkinsonian patients.

The basal ganglia are thought to participate in the control and programming of a variety of motor behaviours. However, the precise nature of this participation still remains to be clarified. This paper examines the proposal that the basal ganglia may serve to scale the amplitude of limb movements, with basal-ganglia dysfunction leading to the inappropriate scaling of intended motor activity. Several authors have suggested that examining the loss of function in Parkinson's-disease (PD) patients offers perhaps the best way of learning about the role played by the basal ganglia in human motor function. While it has previously been reported that PD patients underscale the transport phase of their reach-to grasp movements, it has generally been assumed that the grasp component is normal. In this paper we demonstrate, using a group of hemiparkinson patients, that the scaling of the grasp component is also underscaled in PD patients.

The coordination of bimanual prehension movements in a centrally deafferented patient.

Many everyday tasks require that we use our hands co-operatively, for example, when unscrewing a jar. For tasks where both hands are required to perform the same action, a common motor programme can be used. However, where each hand needs to perform a different action, some degree of independent control of each hand is required. We examined the coordination of bimanual movement kinematics in a female patient recovering from a cerebrovascular accident involving anterior regions of the parietal lobe of the right hemisphere, which resulted in a dense hemianaesthesia of her left arm. Our results indicate that unimanual movements executed by our patient using her non-sensate hand are relatively unimpaired. In contrast, during bimanual movements, reaches executed by our patient using her non-sensate hand show gross directional errors and spatiotemporal irregularities, including the inappropriate coupling of movement velocities. These data are discussed with reference to the role played by limb proprioception in the planning and control of prehension movements.

Attention for action: coordinating bimanual reach-to-grasp movements.

Theories of attention have frequently pointed to the finding that there is a significant performance decrement ('cost') to responding to two different objects concurrently. However, much of the research aimed at investigating how attention is 'divided' in such circumstances has adopted response time (RT) as the measure of interest. In this paper we investigate how attention is 'divided' during the execution of concurrent motor responses, by studying bimanual reach-to-grasp movements directed towards two separate target objects. Furthermore, a key aspect of our study is that each hand is required to perform either the same action (congruent reaches) or a different action (incongruent reaches). Thus in Expt 1 we manipulated the movement amplitude of each hand, while in Expt 2 we manipulated object size. The results of this study suggest that while there is an overall cost associated with carrying out two movements simultaneously, kinematic measures are unaffected by whether the actions required of each hand are the same (congruent) or different (incongruent). The problem of executing incongruent bimanual movements appears to be solved by synchronizing each limb to a common movement duration, while movement velocity and grip aperture are independently scaled. These findings are discussed in relation to theories developed to explain the coordination of the reach-and-grasp phases of unimanual prehension, and in the context of recent theories of attention for action.

The selection and suppression of action: ERP correlates of executive control in humans.

A key aspect of higher cortical function is the ability to selectively withhold or suppress action where appropriate. To examine the time course of executive control we used dense-sensor EEG recording techniques to study event-related electrical potentials (ERPs) during a visual 'go/no-go' task. We show that during both go and no-go trials there is a positive deflection in the ERP, which develops over posterior parietal sensors approximately 350 ms (P300) after the onset of a conditional visual stimulus, but is selectively suppressed during no-go trials. We also show that this modulation of the parietal P300 is preceded by a negative deflection in the ERP recorded over frontal cortex (N2), which is apparent only for no-go trials. We suggest that this signal provides an electrophysiological marker in man for the decision to withhold the execution of a motor response.

The influence of initial hand posture on the expression of prehension parameters.

This paper describes the transport and grasp kinematic parameters associated with four initial hand postures (palm flat and thumb against the hand, palm flat and thumb extended laterally, index and thumb in opposition, and index and thumb in opposition and elbow flexed 90 degrees). A group of healthy adult subjects reached for and picked up a wooden dowel placed midsagittally, at one of three distances (20 cm, 25 cm and 30 cm). The initial posture of the hand and arm altered transport (peak velocity and peak negative acceleration) as well as grasp (peak angle and time to peak angle) parameters, particularly when the elbow was flexed 90 degrees. The pattern of results was reproduced in a pointing paradigm. The findings are discussed in the context of joint space models of reaching.