Hand choice is unaffected by high frequency continuous theta burst transcranial magnetic stimulation to the posterior parietal cortex

The current study used a high frequency TMS protocol known as continuous theta burst stimulation (cTBS) to test a model of hand choice that relies on competing interactions between the hemispheres of the posterior parietal cortex. Based on the assumption that cTBS reduces cortical excitability, the model predicts a significant decrease in the likelihood of selecting the hand contralateral to stimulation. An established behavioural paradigm was used to estimate hand choice in each individual, and these measures were compared across three stimulation conditions: cTBS to the left posterior parietal cortex, cTBS to the right posterior parietal cortex, or sham cTBS. Our results provide no supporting evidence for the interhemispheric competition model. We find no effects of cTBS on hand choice, independent of whether the left or right posterior parietal cortex was stimulated. Our results are nonetheless of value as a point of comparison against prior brain stimulation findings that, in contrast, provide evidence for a causal role for the posterior parietal cortex in hand choice

Spatial Binding Impairments in Visual Working Memory following Temporal Lobectomy

Disorders of the medial temporal lobe (MTL) adversely affect visual working memory (vWM) performance, including feature binding. It is unclear whether these impairments generalize across visual dimensions or are specifically spatial. To address this issue, we compared performance in two tasks of 13 epilepsy patients, who had undergone a temporal lobectomy, and 15 healthy controls. In the vWM task, participants recalled the color of one of two polygons, previously displayed side by side. At recall, a location or shape probe identified the target. In the perceptual task, participants estimated the centroid of three visible disks. Patients recalled the target color less accurately than healthy controls because they frequently swapped the nontarget with the target color. Moreover, healthy controls and right temporal lobectomy patients made more swap errors following shape than space probes. Left temporal lobectomy patients, showed the opposite pattern of errors instead. Patients and controls performed similarly in the perceptual task. We conclude that left MTL damage impairs spatial binding in vWM, and that this impairment does not reflect a perceptual or attentional deficit

The dissociating effects of fear and disgust on multisensory integration in autism: evidence from evoked potentials

BackgroundDeficits in Multisensory Integration (MSI) in ASD have been reported repeatedly and have been suggested to be caused by altered long-range connectivity. Here we investigate behavioral and ERP correlates of MSI in ASD using ecologically valid videos of emotional expressions.MethodsIn the present study, we set out to investigate the electrophysiological correlates of audiovisual MSI in young autistic and neurotypical adolescents. We employed dynamic stimuli of high ecological validity (500 ms clips produced by actors) that depicted fear or disgust in unimodal (visual and auditory), and bimodal (audiovisual) conditions.ResultsWe report robust MSI effects at both the behavioral and electrophysiological levels and pronounced differences between autistic and neurotypical participants. Specifically, neurotypical controls showed robust behavioral MSI for both emotions as seen through a significant speed-up of bimodal response time (RT), confirmed by Miller’s Race Model Inequality (RMI), with greater MSI effects for fear than disgust. Adolescents with ASD, by contrast, showed behavioral MSI only for fear. At the electrophysiological level, the bimodal condition as compared to the unimodal conditions reduced the amplitudes of the visual P100 and auditory P200 and increased the amplitude of the visual N170 regardless of group. Furthermore, a cluster-based analysis across all electrodes revealed that adolescents with ASD showed an overall delayed and spatially constrained MSI effect compared to controls.ConclusionGiven that the variables we measured reflect attention, our findings suggest that MSI can be modulated by the differential effects on attention that fear and disgust produce. We also argue that the MSI deficits seen in autistic individuals can be compensated for at later processing stages by (a) the attention-orienting effects of fear, at the behavioral level, and (b) at the electrophysiological level via increased attentional effort

Decision heuristics in contexts integrating action selection and execution

Heuristics can inform human decision making in complex environments through a reduction of computational requirements (accuracy-resource trade-off) and a robustness to overparameterisation (less-is-more). However, tasks capturing the efficiency of heuristics typically ignore action proficiency in determining rewards. The requisite movement parameterisation in sensorimotor control questions whether heuristics preserve efficiency when actions are nontrivial. We developed a novel action selection-execution task requiring joint optimisation of action selection and spatio-temporal skillful execution. State-appropriate choices could be determined by a simple spatial heuristic, or by more complex planning. Computational models of action selection parsimoniously distinguished human participants who adopted the heuristic from those using a more complex planning strategy. Broader comparative analyses then revealed that participants using the heuristic showed combined decisional (selection) and skill (execution) advantages, consistent with a less-is-more framework. In addition, the skill advantage of the heuristic group was predominantly in the core spatial features that also shaped their decision policy, evidence that the dimensions of information guiding action selection might be yoked to salient features in skill learning

Effects of caffeine on reaction time are mediated by attentional rather than motor processes

Background Caffeine has a well-established effect on reaction times (RTs) but the neurocognitive mechanisms underlying this are unclear. Methods In the present study, 15 female participants performed an oddball task after ingesting caffeine or a placebo, and electroencephalographic data were obtained. Single-trial P3b latencies locked to the stimulus and to the response were extracted and mediation models were fitted to the data to test whether caffeine’s effect on RTs was mediated by its effect on either type of P3b latencies. Results Stimulus-locked latencies showed clear evidence of mediation, with approximately a third of the effect of caffeine on RTs running through the processes measured by stimulus-locked latencies. Caffeine did not affect response-locked latencies, so could not mediate the effect. Discussion These findings are consistent with caffeine’s effect on RTs being a result of its effect on perceptual-attentional processes, rather than motor processes. The study is the first to apply mediation analysis to single-trial P3b data and this technique holds promise for mental chronometric studies into the effects of psychopharmacological agents. The R code for performing the single trial analysis and mediation analysis are included as supplementary materials

Multisensory stimulation in hemianopic patients boosts orienting responses to the hemianopic field and reduces attentional resources to the intact field

Purpose: Lateralised lesions can disrupt inhibitory cross-callosal fibres which maintain interhemispheric equilibrium in attention networks, with a consequent attentional bias towards the ipsilesional field. Some evidence of this imbalance has also been found in hemianopic patients (Tant et al., 2002). The aim of the present study was to reduce this attentional bias in hemianopic patients by using multisensory stimulation capable of activating subcortical structures responsible for orienting attention, such as the superior colliculus. Methods: Eight hemianopic patients underwent a course of multisensory stimulation treatment for two weeks and their behavioural and electrophysiological performance was tested at three time intervals: baseline 1 (before treatment), control baseline 2 (two weeks after baseline 1 and immediately before treatment as a control for practice effects) and finally after treatment. Results: The results show improvements on various clinical measures, on orienting responses in the hemianopic field, and a reduction of electrophysiological activity (P3 amplitude) in response to stimuli presented in the intact visual field. Conclusions: These results suggest that the primary visual deficit in hemianopic patients might be accompanied by an ipsilesional attentional bias which might be reduced by multisensory stimulation

Multisensory stimulation in hemianopic patients boosts orienting responses to the hemianopic field and reduces attentional resources to the intact field

Purpose: Lateralised lesions can disrupt inhibitory cross-callosal fibres which maintain interhemispheric equilibrium in attention networks, with a consequent attentional bias towards the ipsilesional field. Some evidence of this imbalance has also been found in hemianopic patients (Tant et al., 2002). The aim of the present study was to reduce this attentional bias in hemianopic patients by using multisensory stimulation capable of activating subcortical structures responsible for orienting attention, such as the superior colliculus. Methods: Eight hemianopic patients underwent a course of multisensory stimulation treatment for two weeks and their behavioural and electrophysiological performance was tested at three time intervals: baseline 1 (before treatment), control baseline 2 (two weeks after baseline 1 and immediately before treatment as a control for practice effects) and finally after treatment. Results: The results show improvements on various clinical measures, on orienting responses in the hemianopic field, and a reduction of electrophysiological activity (P3 amplitude) in response to stimuli presented in the intact visual field. Conclusions: These results suggest that the primary visual deficit in hemianopic patients might be accompanied by an ipsilesional attentional bias which might be reduced by multisensory stimulation

Reorganization of sensorimotor representations of the intact limb after upper but not lower limb traumatic amputation

It is becoming increasingly clear that limb loss induces wider spread reorganization of representations of the body that are nonadjacent to the affected cortical territory. Data from upper extremity amputees reveal intrusion of the representation of the ipsilateral intact limb into the former hand territory. Here we test for the first time whether this reorganization of the intact limb into the deprived cortex is specific to the neurological organization of the upper limbs or reflects large scale adaptation that is triggered by any unilateral amputation. BOLD activity was measured as human subjects with upper limb and lower limb traumatic amputation and their controls moved the toes on each foot, open and closed each hand and pursed their lips. Subjects with amputation were asked to imagine moving the missing limb while remaining still. Bayesian pattern component modeling of fMRI data showed that intact ipsilateral movements and contralateral movements of the hand and foot were distinctly represented in the deprived sensorimotor cortex years after upper limb amputation. In contrast, there was evidence reminiscent of contralateral specificity for hand and foot movements following lower limb amputation, like that seen in controls. We propose the cortical reorganization of the intact limb to be a function of use-dependent plasticity that is more specific to the consequence of upper limb loss of forcing an asymmetric reliance on the intact hand and arm. The contribution of this reorganization to phantom pain or a heightened risk of overuse and resultant maladaptive plasticity needs investigating before targeting such reorganization in intervention