Sustaining attention in affective contexts during adolescence: age-related differences and association with elevated symptoms of depression and anxiety

Sustained attention, a key cognitive skill that improves during childhood and adolescence, tends to be worse in some emotional and behavioural disorders. Sustained attention is typically studied in non-affective task contexts; here, we used a novel task to index performance in affective versus neutral contexts across adolescence (N = 465; ages 11-18). We asked whether: (i) performance would be worse in negative versus neutral task contexts; (ii) performance would improve with age; (iii) affective interference would be greater in younger adolescents; (iv) adolescents at risk for depression and higher in anxiety would show overall worse performance; and (v) would show differential performance in negative contexts. Results indicated that participants performed more poorly in negative contexts and showed age-related performance improvements. Those at risk of depression performed more poorly than those at lower risk. However, there was no difference between groups as a result of affective context. For anxiety there was no difference in performance as a function of severity. However, those with higher anxiety showed less variance in their reaction times to negative stimuli than those with lower anxiety. One interpretation is that moderate levels of emotional arousal associated with anxiety make individuals less susceptible to the distracting effects of negative stimuli.

Puberty and risky decision-making in male adolescents

Pubertal development is a potential trigger for increases in risk-taking behaviours during adolescence. Here, we sought to investigate the relationship between puberty and neural activation during risky decision-making in males using functional magnetic resonance imaging (fMRI). Forty-seven males aged 12.5-14.5 years completed an fMRI risk-taking task (BART) and reported their tendencies for risky decision-making using a self-report questionnaire. Puberty was assessed through self-reported pubertal status and salivary testosterone levels. Testosterone concentration, but not physical pubertal status, was positively correlated with self-reported risk-taking behaviour, while neither was correlated with BART performance. Across the whole sample, participants had greater activation of the bilateral nucleus accumbens and right caudate on trials when they made a successful risky decision compared to trials when they made a safe choice or when their risky decision was unsuccessful. There was a negative correlation between pubertal stage and brain activation during unsuccessful risky decision-making trials compared within unsuccessful control trials. Males at a lower stage of pubertal development showed increased activation in the left insula, right cingulate cortex, dorsomedial prefrontal cortex (dmPFC), right putamen and right orbitofrontal cortex (OFC) relative to more pubertally mature males during trials when they chose to take a risk and the balloon popped compared to when they watched the computer make an unsuccessful risky decision. Less pubertally mature males also showed greater activation in brain regions including the dmPFC, right temporal and frontal cortices, right OFC, right hippocampus and occipital cortex in unsuccessful risky trials compared to successful risky trials. These results suggest a puberty-related shift in neural activation within key brain regions when processing outcomes of risky decisions, which may reduce their sensitivity to negative feedback, and in turn contribute to increases in adolescent risk-taking behaviours.

Susceptibility to prosocial and antisocial influence in adolescence

Introduction

Adolescents are particularly susceptible to social influence and previous studies have shown that this susceptibility decreases with age. The current study used a cross-sectional experimental paradigm to investigate the effect of age and puberty on susceptibility to both prosocial and antisocial influence.

Methods

Participants (N = 520) aged 11–18 from London and Cambridge (United Kingdom) rated how likely they would be to engage in a prosocial (e.g. “help a classmate with their work”) or antisocial (e.g. “make fun of a classmate”) act. They were then shown the average rating (in fact fictitious) that other adolescents had given to the same question, and were then asked to rate the same behaviour again.

Results

Both prosocial and antisocial influence decreased linearly with age, with younger adolescents being more socially influenced when other adolescents’ ratings were more prosocial and less antisocial than their own initial rating. Both antisocial and prosocial influence significantly decreased across puberty for boys but not girls (independent of age).

Conclusions

These findings suggest that social influence declines with increasing maturity across adolescence. However, the exact relationship between social influence and maturity is dependent on the nature of the social influence and gender. Understanding when adolescents are most susceptible to different types of social influence, and how this might influence their social behaviour, has important implications for understanding adolescent social development.

Neural correlates of social influence on risk perception during development

Studies have shown that adolescents are more likely than adults to take risks in the presence of peers than when alone, and that young adolescents' risk perception is more influenced by other teenagers than by adults. The current fMRI study investigated the effect of social influence on risk perception in female adolescents (aged 12-14) and adults (aged 23-29). Participants rated the riskiness of everyday situations and were then informed about the (alleged) risk ratings of a social influence group (teenagers or adults), before rating each situation again. The results showed that adolescents adjusted their ratings to conform with others more than adults did, and both age groups were influenced more by adults than by teenagers. When there was a conflict between the participants' own risk ratings and the ratings of the social influence group, activation was increased in the posterior medial frontal cortex, dorsal cingulate cortex and inferior frontal gyrus in both age groups. In addition, there was greater activation during no-conflict situations in the right middle frontal gyrus and bilateral parietal cortex in adults compared with adolescents. These results suggest that there are behavioral and neural differences between adolescents and adults in conflict and no-conflict social situations.

PI3Kδ inhibition elicits anti-leukemic effects through Bim-dependent apoptosis

PI3Kδ plays pivotal roles in the maintenance, proliferation and survival of malignant B-lymphocytes. Although not curative, PI3Kδ inhibitors (PI3Kδi) demonstrate impressive clinical efficacy and, alongside other signaling inhibitors, are revolutionizing the treatment of hematological malignancies. However, only limited in vivo data are available regarding their mechanism of action. With the rising number of novel treatments, the challenge is to identify combinations that deliver curative regimes. A deeper understanding of the molecular mechanism is required to guide these selections. Currently, immunomodulation, inhibition of B-cell receptor signaling, chemokine/cytokine signaling and apoptosis represent potential therapeutic mechanisms for PI3Kδi. Here we characterize the molecular mechanisms responsible for PI3Kδi-induced apoptosis in an in vivo model of chronic lymphocytic leukemia (CLL). In vitro, PI3Kδi-induced substantive apoptosis and disrupted microenvironment-derived signaling in murine (Eμ-Tcl1) and human (CLL) leukemia cells. Furthermore, PI3Kδi imparted significant therapeutic responses in Eμ-Tcl1-bearing animals and enhanced anti-CD20 monoclonal antibody therapy. Responses correlated with upregulation of the pro-apoptotic BH3-only protein Bim. Accordingly, Bim-/- Eμ-Tcl1 Tg leukemias demonstrated resistance to PI3Kδi-induced apoptosis were refractory to PI3Kδi in vivo and failed to display combination efficacy with anti-CD20 monoclonal antibody therapy. Therefore, Bim-dependent apoptosis represents a key in vivo therapeutic mechanism for PI3Kδi, both alone and in combination therapy regimes.

EGR2 mutations define a new clinically aggressive subgroup of chronic lymphocytic leukemia

Recurrent mutations within EGR2 were recently reported in advanced-stage chronic lymphocytic leukemia (CLL) patients and associated with a worse outcome. To study their prognostic impact, 2403 CLL patients were examined for mutations in the EGR2 hotspot region including a screening (n=1283) and two validation cohorts (UK CLL4 trial patients, n=366; CLL Research Consortium (CRC) patients, n=490). Targeted deep-sequencing of 27 known/postulated CLL driver genes was also performed in 38 EGR2-mutated patients to assess concurrent mutations. EGR2 mutations were detected in 91/2403 (3.8%) investigated cases, and associated with younger age at diagnosis, advanced clinical stage, high CD38 expression and unmutated IGHV genes. EGR2-mutated patients frequently carried ATM lesions (42%), TP53 aberrations (18%) and NOTCH1/FBXW7 mutations (16%). EGR2 mutations independently predicted shorter time-to-first-treatment (TTFT) and overall survival (OS) in the screening cohort; they were confirmed associated with reduced TTFT and OS in the CRC cohort and independently predicted short OS from randomization in the UK CLL4 cohort. A particularly dismal outcome was observed among EGR2-mutated patients who also carried TP53 aberrations. In summary, EGR2 mutations were independently associated with an unfavorable prognosis, comparable to CLL patients carrying TP53 aberrations, suggesting that EGR2-mutated patients represent a new patient subgroup with very poor outcome.

The influence of prior expectations on facial expression discrimination in schizophrenia

BACKGROUND

Belief inflexibility is a thinking style observed in patients with schizophrenia, in which patients tend to refute evidence that runs counter to their prior beliefs. This bias has been related to a dominance of prior expectations (prior beliefs) over incoming sensory evidence. In this study we investigated the reliance on prior expectations for the processing of emotional faces in schizophrenia.

METHOD

Eighteen patients with schizophrenia and 18 healthy controls were presented with sequences of emotional (happy, fearful, angry or neutral) faces. Perceptual decisions were biased towards a particular expression by a specific instruction at the start of each sequence, referred to as the context in which stimuli occurred. Participants were required to judge the emotion on each face and the effect of the context on emotion discrimination was investigated.

RESULTS

For threatening emotions (anger and fear), there was a performance cost for facial expressions that were incongruent with, and perceptually close to, the expression named in the instruction. For example, for angry faces, participants in both groups made more errors and reaction times (RTs) were longer when they were asked to look out for fearful faces compared with the other contexts. This bias against sensory evidence that runs counter to prior information was stronger in the patients, evidenced by a group by context interaction in accuracy and RTs for anger and fear respectively.

CONCLUSIONS

Overall, the present data suggest an overdependence on prior expectations for threatening stimuli, reflecting belief inflexibility, in schizophrenia.

Effects of age and MAOA genotype on the neural processing of social rejection

Adolescents are often sensitive to peer rejection, a factor that might contribute to the risk of affective disorder in this age group. Previous studies suggest a significant overlap among socioaffective brain regions involved in the response to social rejection, regions continuing to develop functionally during adolescence and regions influenced by monoamine oxidase A (MAOA) polymorphism. The current study investigated whether the neural response to social rejection is functionally immature in adolescents compared with adults, and whether these responses are modulated by MAOA genotype. Blood-oxygen-level-dependent response was measured with functional magnetic resonance imaging during a rejection-themed emotional Stroop task in 19 adolescents (aged 14-16) and 16 adults (aged 23-28) genotyped for MAOA polymorphism. Similar numbers of MAOA-L and MAOA-H carriers were recruited to maximize power to detect genotype effects. Main effects of rejection stimuli (relative to neutral and acceptance control stimuli) were seen in predicted socioaffective brain regions. Adolescents did not show the adult pattern of modulation by rejection stimuli in the right ventrolateral prefrontal cortex, suggesting continued functional maturation of this regulatory region during adolescence. Age and genotype interacted in the left amygdala, in which the predicted effect of genotype on responses to rejection stimuli was seen in the adults, but not in the adolescents. The data suggest continued functional development of the circuitry underlying the processing of social rejection between adolescence and adulthood, and show that the effects of MAOA genotype on neural responses may vary with age.

Thinking about intentions

In this fMRI study, we investigated the convergence of underlying neural networks in thinking about a scenario involving one's own intentional action and its consequences and setting up and holding in mind an intention to act. A factorial design was employed comprising two factors: i. Causality (intentional or physical events) and ii. Prospective Memory (present or absent). In each condition, subjects answered questions about various hypothetical scenarios, which related either to the link between the subject's own intentions and consequential actions (Intentional Causality) or to the link between a natural, physical event and its consequences (Physical Causality). A prospective memory task was embedded in half the blocks. In this task, subjects were required to keep in mind an intention (to press a key on seeing a red stimulus background) whilst carrying out the ongoing Causality task. Answering questions about intentional causality versus physical causality activated a network of regions that have traditionally been associated with Theory of Mind, including the medial prefrontal cortex (mPFC), the superior temporal sulcus and the temporal poles bilaterally. In addition, the precuneus bordering with posterior cingulate cortex, an area involved in self-awareness and self-related processing, was activated more when thinking about intentional causality. In the prospective memory task, activations were found in the right parietal cortex, frontopolar cortex (BA 10) and precuneus. Different subregions within the precuneus/posterior cingulate cortex were activated in both main effects of intentional causality and prospective memory. Therefore, the precuneus/posterior cingulate cortex subserves separately thinking about one's own intentions and consequent actions and bearing in mind an intention to make an action. Previous studies have shown that prospective memory, requiring the formation of an intention and the execution of a corresponding action, is associated with decreased activation in the dorsal mPFC, close to the region activated in Theory of Mind tasks. Here, we found that holding in mind an intention to act and at the same time thinking about an intentional action led to reduced activity in a dorsal section of the mPFC. This was a different region from a more anterior, inferior dorsal mPFC region that responded to intentional causality. This suggests that different regions of mPFC play different roles in thinking about intentions.

Somatosensory activations during the observation of touch and a case of vision–touch synaesthesia

In this study, we describe a new form of synaesthesia in which visual perception of touch elicits conscious tactile experiences in the perceiver. We describe a female subject (C) for whom the observation of another person being touched is experienced as tactile stimulation on the equivalent part of C's own body. Apart from this clearly abnormal synesthetic experience, C is healthy and normal in every other way. In this study, we investigate whether C's 'mirrored touch' synesthetic experience is caused by overactivity in the neural system that responds to the observation of touch. A functional MRI experiment was designed to investigate the neural system involved in the perception of touch in a group of 12 non-synesthetic control subjects and in C. We investigated neural activity to the observation of touch to a human face or neck compared with the observation of touch to equivalent regions on an object. Furthermore, to investigate the somatosensory topography of the activations during observation of touch, we compared activations when observing a human face or neck being touched with activations when the subjects themselves were touched on their own face or neck. The results demonstrated that the somatosensory cortex was activated in the non-synesthetic subjects by the mere observation of touch and that this activation was somatotopically organized such that observation of touch to the face activated the head area of primary somatosensory cortex, whereas observation of touch to the neck did not. Moreover, in non-synesthetic subjects, the brain's mirror system-comprising premotor cortex, superior temporal sulcus and parietal cortex-was activated by the observation of touch to another human more than to an object. C's activation patterns differed in three ways from those of the non-synesthetic controls. First, activations in the somatosensory cortex were significantly higher in C when she observed touch. Secondly, an area in left premotor cortex was activated in C to a greater extent than in the non-synesthetic group. Thirdly, the anterior insula cortex bilaterally was activated in C, but there was no evidence of such activation in the non-synesthetic group. The results suggest that, in C, the mirror system for touch is overactive, above the threshold for conscious tactile perception.

The detection of intentional contingencies in simple animations in patients with delusions of persecution

BACKGROUND

It has been proposed that delusions of persecution are caused by the tendency to over-attribute malevolent intentions to other people's actions. One aspect of intention attribution is detecting contingencies between an agent's actions and intentions. Here, we used simplified stimuli to test the hypothesis that patients with persecutory delusions over-attribute contingency to agents' movements.

METHOD

Short animations were presented to three groups of subjects: (1) schizophrenic patients; (2) patients with affective disorders; and (3) normal control subjects. Patients were divided on the basis of the presence or absence of delusions of persecution. Participants watched four types of film featuring two shapes. In half the films one shape's movement was contingent on the other shape. Contingency was either 'intentional': one shape moved when it 'saw' another shape; or 'mechanical': one shape was launched by the other shape. Subjects were asked to rate the strength of the relationship between the movement of the shapes.

RESULTS

Normal control subjects and patients without delusions of persecution rated the relationship between the movement of the shapes as stronger in both mechanical and intentional contingent conditions than in non-contingent conditions. In contrast, there was no significant difference between the ratings of patients with delusions of persecution for the conditions in which movement was animate. Patients with delusions of persecution perceived contingency when there was none in the animate non-contingent condition.

CONCLUSIONS

The results suggest that delusions of persecution may be associated with the over-attribution of contingency to the actions of agents.

The detection of contingency and animacy from simple animations in the human brain

Contingencies between objects and people can be mechanical or intentional-social in nature. In this fMRI study we used simplified stimuli to investigate brain regions involved in the detection of mechanical and intentional contingencies. Using a factorial design we manipulated the 'animacy' and 'contingency' of stimulus movement, and the subject's attention to the contingencies. The detection of mechanical contingency between shapes whose movement was inanimate engaged the middle temporal gyrus and right intraparietal sulcus. The detection of intentional contingency between shapes whose movement was animate activated superior parietal networks bilaterally. These activations were unaffected by attention to contingency. Additional regions, the right middle frontal gyrus and left superior temporal sulcus, became activated by the animate-contingent stimuli when subjects specifically attended to the contingent nature of the stimuli. Our results help to clarify neural networks previously associated with 'theory of mind' and agency detection. In particular, the results suggest that low-level perception of agency in terms of objects reacting to other objects at a distance is processed by parietal networks. In contrast, the activation of brain regions traditionally associated with theory of mind tasks appears to require attention to be directed towards agency and contingency.

Delusions of alien control in the normal brain

Delusions of alien control, or passivity experiences, are symptoms associated with schizophrenia in which patients misattribute self-generated actions to an external source. In this study hypnosis was used to induce a similar misattribution of self-generated movement in normal, healthy individuals. Positron Emission Tomography (PET) was employed to investigate the neural correlates of active movements correctly attributed to the self, compared with identical active movements misattributed to an external source. Active movements attributed to an external source resulted in significantly higher activations in the parietal cortex and cerebellum than identical active movements correctly attributed to the self. We suggest that, as a result of hypnotic suggestion, the functioning of this cerebellar-parietal network is altered so that self-produced actions are experienced as being external. These results have implications for the brain mechanisms underlying delusions of control, which may be associated with overactivation of the cerebellar-parietal network.

An interference effect of observed biological movement on action

It has been proposed that actions are intrinsically linked to perception and that imagining, observing, preparing, or in any way representing an action excites the motor programs used to execute that same action. There is neurophysiological evidence that certain brain regions involved in executing actions are activated by the mere observation of action (the so-called "mirror system;" ). However, it is unknown whether this mirror system causes interference between observed and simultaneously executed movements. In this study we test the hypothesis that, because of the overlap between action observation and execution, observed actions should interfere with incongruous executed actions. Subjects made arm movements while observing either a robot or another human making the same or qualitatively different arm movements. Variance in the executed movement was measured as an index of interference to the movement. The results demonstrate that observing another human making incongruent movements has a significant interference effect on executed movements. However, we found no evidence that this interference effect occurred when subjects observed a robotic arm making incongruent movements. These results suggest that the simultaneous activation of the overlapping neural networks that process movement observation and execution infers a measurable cost to motor control.

How the brain perceives causality: an event-related fMRI study

Detection of the causal relationships between events is fundamental for understanding the world around us. We report an event-related fMRI study designed to investigate how the human brain processes the perception of mechanical causality. Subjects were presented with mechanically causal events (in which a ball collides with and causes movement of another ball) and non-causal events (in which no contact is made between the balls). There was a significantly higher level of activation of V5/MT/MST bilaterally, the superior temporal sulcus bilaterally and the left intraparietal sulcus to causal relative to non-causal events. Directing attention to the causal nature of the stimuli had no significant effect on the neural processing of the causal events. These results support theories of causality suggesting that the perception of elementary mechanical causality events is automatically processed by the visual system.

The cerebellum is involved in predicting the sensory consequences of action

We used H2(15)O PET to examine neural responses to parametrically varied degrees of discrepancy between the predicted and actual sensory consequences of movement. Subjects used their right hand to move a robotic arm. The motion of this robotic arm determined the position of a second foam-tipped robotic arm, which made contact with the subject's left palm. Using this robotic interface, computer controlled delays were introduced between the movement of the right hand and the tactile stimulation on the left. Activity in the right lateral cerebellar cortex showed a positive correlation with delay. These results suggest the cerebellum is involved in signalling the sensory discrepancy between the predicted and actual sensory consequences of movements.

Abnormalities in the awareness and control of action

Much of the functioning of the motor system occurs without awareness. Nevertheless, we are aware of some aspects of the current state of the system and we can prepare and make movements in the imagination. These mental representations of the actual and possible states of the system are based on two sources: sensory signals from skin and muscles, and the stream of motor commands that have been issued to the system. Damage to the neural substrates of the motor system can lead to abnormalities in the awareness of action as well as defects in the control of action. We provide a framework for understanding how these various abnormalities of awareness can arise. Patients with phantom limbs or with anosognosia experience the illusion that they can move their limbs. We suggest that these representations of movement are based on streams of motor commands rather than sensory signals. Patients with utilization behaviour or with delusions of control can no longer properly link their intentions to their actions. In these cases the impairment lies in the representation of intended movements. The location of the neural damage associated with these disorders suggests that representations of the current and predicted state of the motor system are in parietal cortex, while representations of intended actions are found in prefrontal and premotor cortex.

The perception of self-produced sensory stimuli in patients with auditory hallucinations and passivity experiences: evidence for a breakdown in self-monitoring

BACKGROUND

To test the hypothesis that certain psychotic symptomatology is due to a defect in self-monitoring, we investigated the ability of groups of psychiatric patients to differentiate perceptually between self-produced and externally produced tactile stimuli.

METHODS

Responses to tactile stimulation were assessed in three groups of subjects: schizophrenic patients; patients with bipolar affective disorder or depression; and normal control subjects. Within the psychiatric groups subjects were divided on the basis of the presence or absence of auditory hallucinations and/or passivity experiences. The subjects were asked to rate the perception of a tactile sensation on the palm of their left hand. The tactile stimulation was either self-produced by movement of the subject's right hand or externally produced by the experimenter.

RESULTS

Normal control subjects and those psychiatric patients with neither auditory hallucinations nor passivity phenomena experienced self-produced stimuli as less intense, tickly and pleasant than identical, externally produced tactile stimuli. In contrast, psychiatric patients with these symptoms did not show a decrease in their perceptual ratings for tactile stimuli produced by themselves as compared with those produced by the experimenter. This failure to show a difference in perception between self-produced and externally produced stimuli appears to relate to the presence of auditory hallucinations and/or passivity experiences rather than to the diagnosis of schizophrenia.

CONCLUSIONS

We propose that auditory hallucinations and passivity experiences are associated with an abnormality in the self-monitoring mechanism that normally allows us to distinguish self-produced from externally produced sensations.

Why can't you tickle yourself?

It is well known that you cannot tickle yourself. Here, we discuss the proposal that such attenuation of self-produced tactile stimulation is due to the sensory predictions made by an internal forward model of the motor system. A forward model predicts the sensory consequences of a movement based on the motor command. When a movement is self-produced, its sensory consequences can be accurately predicted, and this prediction can be used to attenuate the sensory effects of the movement. Studies are reviewed that demonstrate that as the discrepancy between predicted and actual sensory feedback increases during self-produced tactile stimulation there is a concomitant decrease in the level of sensory attenuation and an increase in tickliness. Functional neuroimaging studies have demonstrated that this sensory attenuation might be mediated by somatosensory cortex and anterior cingulate cortex: these areas are activated less by a self-produced tactile stimulus than by the same stimulus when it is externally produced. Furthermore, evidence suggests that the cerebellum might be involved in generating the prediction of the sensory consequences of movement. Finally, recent evidence suggests that this predictive mechanism is abnormal in patients with auditory hallucinations and/or passivity experiences.

Four-year PhDs in neuroscience: an assessment after four years

In 1996, as an innovation for the UK, the Wellcome Trust set up two 'American style' four-year PhD programmes in neuroscience, with an initial year of broad training followed by a three-year PhD. Here, some of the first cohort of students, who are soon to graduate and the coordinators of the programmes, give their views on this experiment in neuroscience research training.

The cerebellum contributes to somatosensory cortical activity during self-produced tactile stimulation

We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. The somatosensory cortex showed increased levels of activity when the stimulus was externally produced. In the cerebellum there was less activity associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements and providing the signal that is used to attenuate the sensory response to self-generated stimulation. In this paper, we use regression analyses to test this hypothesis explicitly. Specifically, we predicted that activity in the cerebellum contributes to the decrease in somatosensory cortex activity during self-produced tactile stimulation. Evidence in favor of this hypothesis was obtained by demonstrating that activity in the thalamus and primary and secondary somatosensory cortices significantly regressed on activity in the cerebellum when tactile stimuli were self-produced but not when they were externally produced. This supports the proposal that the cerebellum is involved in predicting the sensory consequences of movements. In the present study, this prediction is accurate when tactile stimuli are self-produced relative to when they are externally produced, and is therefore used to attenuate the somatosensory response to the former type of tactile stimulation but not the latter.

Spatio-temporal prediction modulates the perception of self-produced stimuli

We investigated why self-produced tactile stimulation is perceived as less intense than the same stimulus produced externally. A tactile stimulus on the palm of the right hand was either externally produced, by a robot or self-produced by the subject. In the conditions in which the tactile stimulus was self-produced, subjects moved the arm of a robot with their left hand to produce the tactile stimulus on their right hand via a second robot. Subjects were asked to rate intensity of the tactile sensation and consistently rated self-produced tactile stimuli as less tickly, intense, and pleasant than externally produced tactile stimuli. Using this robotic setup we were able to manipulate the correspondence between the action of the subjects' left hand and the tactile stimulus on their right hand. First, we parametrically varied the delay between the movement of the left hand and the resultant movement of the tactile stimulus on the right hand. Second, we implemented varying degrees of trajectory perturbation and varied the direction of the tactile stimulus movement as a function of the direction of left-hand movement. The tickliness rating increased significantly with increasing delay and trajectory perturbation. This suggests that self-produced movements attenuate the resultant tactile sensation and that a necessary requirement of this attenuation is that the tactile stimulus and its causal motor command correspond in time and space. We propose that the extent to which self-produced tactile sensation is attenuated (i.e., its tickliness) is proportional to the error between the sensory feedback predicted by an internal forward model of the motor system and the actual sensory feedback produced by the movement.

CCR7 (EBI1) receptor down-regulation in asthma: differential gene expression in human CD4+ T lymphocytes

Asthma is an inflammatory disorder, and the CD4+ T lymphocyte plays a key role in mediating the inflammatory response. We used a high-density grid, hybridization-based, differential gene expression technology to analyse molecular mechanisms underlying in vivo CD4+ T-cell activation in both steroid-resistant asthma (SRA) and steroid-sensitive asthma (SSA). Hybridization of radioactively-labelled first-strand cDNAs prepared from different biological samples, to identical high-density gridded arrays of PCR amplicons derived from cDNA clone inserts immobilized on nylon membranes, was compared by phosphorimaging. Hybridization data were captured and processed using image analysis software that can identify the location and signal intensity of each hybridized cDNA. This produces a hierarchy of signals of differing intensities between the two grids, representing differential gene expression in the two different RNA samples. CCR7 (EBI1), a lymphocyte-specific G-protein-coupled receptor, was down-regulated in the CD4+ T cells of SRA and SSA non-atopic, compared to non-asthmatic non-atopic individuals. This observation is intriguing given that CCR7 and its ligand EBI1-Ligand Chemokine (ELC), may play a role in the migration and homing of normal lymphocytes. Also, TNFR2 is up-regulated in both SSA non-atopic and SRA atopic as compared to non-asthmatic controls. LAMR1 is down-regulated in CD4+ T cells of SRA compared to non-asthmatic individuals, irrespective of their atopic status. These could be general phenomena resulting from cytokine release.

Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanism involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

Identification of two novel diurnal genes by screening of a rat brain cDNA library

While the hypothalamus is fundamental for sleep and circadian regulation, the molecular mechanisms involved are poorly understood. We have used a differential gene expression technique to identify hypothalamic genes which have altered expression in rat sleep periods. Complex cDNA probes from rat hypothalami removed at Zeitgeber times 4 and 15 were hybridised to rat brain cDNA library girds. From 30 differentially expressed clones, six were further analysed and two were confirmed to exhibit increased expression at Zeitgeber time 4. A Northern blot hybridization of brain, heart, kidney, lung, testis and skin mRNA showed that both clones were brain specific. Therefore, we have identified two novel brain specific diurnally expressed hypothalamic genes. Both genes may have roles in sleep or circadian regulation.

Central cancellation of self-produced tickle sensation

A self-produced tactile stimulus is perceived as less ticklish than the same stimulus generated externally. We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. More activity was found in somatosensory cortex when the stimulus was externally produced. In the cerebellum, less activity was associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements, providing the signal that is used to cancel the sensory response to self-generated stimulation.

GLUT5 expression and fructose transport in human skeletal muscle

Biochemical and immunocytochemical studies have revealed that, in addition to GLUT1 and GLUT4, human skeletal muscle also expresses the GLUT5 hexose transporter. The subcellular distribution of GLUT5 is distinct from that of GLUT4, being localised exclusively in the sarcolemmal membrane. The substrate selectivity of GLUT5 is also considered to be different to that of GLUT1 and GLUT4 in that it operates primarily as a fructose transporter. Consistent with this suggestion studies in isolated human sarcolemmal vesicles have shown that fructose transport obeys saturable kinetics with a Vmax of 477 +/- 37 pmol.mg protein-1 min-1 and a Km of 8.3 +/- 1.2 mM. Unlike glucose uptake, fructose transport in sarcolemmal vesicles was not inhibited by cytochalasin B suggesting that glucose and fructose are unlikely to share a common route of entry into human muscle. Muscle exercise, which stimulates glucose uptake through the increased translocation of GLUT4 to the plasma membrane, does not increase fructose transport or sarcolemmal GLUT5 content. In contrast, muscle inactivity, induced as a result of limb immobilisation, caused a significant reduction in muscle GLUT4 expression with no detectable effects on GLUT5. The presence of a fructose transporter in human muscle is compatible with studies showing that this tissue can utilise fructose for both glycolysis and glycogenesis. However, the full extent to which provision of fructose via GLUT5 is important in meeting the energy requirements of human muscle during both physiological and pathophysiological circumstances remains an issue requiring further investigation.

Predicting the consequences of our own actions: the role of sensorimotor context estimation

During self-generated movement it is postulated that an efference copy of the descending motor command, in conjunction with an internal model of both the motor system and environment, enables us to predict the consequences of our own actions (von Helmholtz, 1867; Sperry, 1950; von Holst, 1954; Wolpert, 1997). Such a prediction is evident in the precise anticipatory modulation of grip force seen when one hand pushes on an object gripped in the other hand (Johansson and Westling, 1984; Flanagan and Wing, 1933). Here we show that self-generation is not in itself sufficient for such a prediction. We used two robots to simulate virtual objects held in one hand and acted on by the other. Precise predictive grip force modulation of the restraining hand was highly dependent on the sensory feedback to the hand producing the load. The results show that predictive modulation requires not only that the movement is self-generated, but also that the efference copy and sensory feedback are consistent with a specific context; in this case, the manipulation of a single object. We propose a novel computational mechanism whereby the CNS uses multiple internal models, each corresponding to a different sensorimotor context, to estimate the probability that the motor system is acting within each context.

How do we predict the consequences of our actions? A functional imaging study

Humans are readily able to distinguish expected and unexpected sensory events. Whether a single mechanism underlies this ability is unknown. The most common type of expected sensory events are those generated as a consequence of self-generated actions. Using H2 15O PET, we studied brain responses to such predictable sensory events (tones) and to similar unpredictable events and especially how the processing of predictable sensory events is modified by the context of a causative self-generated action. Increases in activity when the tones were unpredictable were seen in the inferior and superior temporal lobe bilaterally, the right parahippocampal gyrus and right parietal cortex. Self-generated actions produced activity in a number of motor and premotor areas, including dorsolateral prefrontal cortex. We observed an interaction between the predictability of stimuli and self-generated actions in several areas, including the medial posterior cingulate cortex, left insula, dorsomedial thalamus, superior colliculus and right inferior temporal cortex. This modulation of activity associated with stimulus predictability in the context of self-generated actions implies that these areas may be involved in self-monitoring processes. Detection of expected stimuli and the detection of the sensory consequences of self-generated actions appear to be functionally distinct processes, and are carried out in different cortical areas. These observations support theoretical approaches to cognition that postulate the existence of a self-monitoring system.

Effects of limb immobilization on cytochrome c oxidase activity and GLUT4 and GLUT5 protein expression in human skeletal muscle

1. We investigated the effects of limb immobilization (for 1 or 6 weeks) in a long leg cast after a closed tibial fracture (n = 11). Biopsies of vastus lateralis were taken on admission and after either 1 week (n = 5) or 6 weeks (n = 6) and analysed for muscle fibre type characteristics, cytochrome c oxidase activity and the abundance of GLUT4 and GLUT5 hexose transporters. 2. After 1 week of immobilization there was a significant decrease (8%) in the cross-sectional area of type I, but not type II, muscle fibers and in the protein-DNA ratio (16%) compared with the initial biopsy. Six weeks of immobilization led to further muscle atrophy compared with the initial biopsy and a further reduction in the cross-sectional area of both type I and II fibres (29% and 36% decrease respectively) and in the protein-DNA ratio (25%). No changes were observed in the free leg after 1 week. However, at th end of the 6 week study period, the cross-sectional area of boty type I and II fibres of the free leg were increased (7% and 5%) and there was significant increase in the protein-DNA ratio (14%), indicating a net increase in muscle protein content. 3. Assay for cytochrome c oxidase activity showed significant reduction after 1 (30%) or 6 weeks (36%) of immobilization, reflecting a reduced capacity for oxidative metabolism. No significant changes in activity were observed in muscle from the free leg after 1 or 6 weeks of study. 4. The concentrations of GLUT4 and GLUT5 protein were determined by Western blot analysis. Limb immobilization induced a marked (50%) reduction in muscle GLUT4 protein concentration after 1 week that persisted for 6 weeks. A transient but significant increase (approximately twofold) in GLUT4 concentration was detected in muscle from the free leg after 1 week, but this returned to pre-imobilization values at 6 week. Unlike GLUT4, no significant changes in the abundance of the GLUT5 protein were detected in either the immobilized or free leg at the end of the 1 or 6 week periods. 5. The present findings indicate that disuse rapidly induces a selective loss of activity and abundance of some non-myofibrillar proteins in humans. The decrease in GLUT4 protein abundance and cytochrome c oxidase activity during muscle disuse is consistent with a decreased capacity for glucose uptake and with a lower oxidative potential of inactive muscle. The lack of any major changes in GLUT5 protein abundance during limb immobilization indicates that the expression of some non-myofibrillar proteins is differentially regulated in response to muscle disuse.

The GLUT5 hexose transporter is also localized to the basolateral membrane of the human jejunum

The intestine is a major site of expression of the human GLUT5 hexose transporter, which is thought to be localized exclusively to the brush border membrane (BBM) where its major role is likely to be in the absorption of fructose. In this study we present novel biochemical and morphological evidence showing that the GLUT5 transporter is also expressed in the basolateral membrane (BLM) of the human intestine. BBM and BLM were isolated by fractionation of human jejunum. BBM were enriched with alkaline phosphatase activity by over 9-fold relative to a crude jejunal homogenate and contained immunoreactive sucrase-isomaltase and GLUT5 proteins. By contrast the BBM fraction was substantially depleted of immunoreactive a1 subunits of the Na,K-ATPase and GLUT2 glucose transporters which were abundantly present in the BLM fraction. This BLM fraction was enriched by over 11-fold in potassium-stimulated phosphatase activity relative to the crude homogenate; BLM also reacted to immunological probes for GLUT5 but showed no observable reactivity with antibodies directed against sucrase-isomaltase. Quantitative immunoblotting revealed that the BBM and BLM contained near equal amounts of GLUT5 per mg of membrane protein. Immunogold localization of GLUT5 on ultrathin sections of human jejunum showed that GLUT5 was present in both apical BBM and BLM. This gold labelling was absent when antiserum was pre-incubated with the antigenic peptide corresponding to a specific C-terminal sequence of human GLUT5. Quantitative analyses of the number of gold particles per unit length of BBM and BLM indicated that the mean density of gold labelling was marginally greater in the BBM (0.399 gold particles/micrometer) than in the BLM (0.293 gold particle/micrometer). The localization of GLUT5 in the BLM of the human jejunum may suggest that it specifically participates in the transfer of fructose across the basal membrane of the enterocyte.