Response times are affected by mispredictions in a stochastic game

Acting as a goalkeeper in a video-game, a participant is asked to predict the successive choices of the penalty taker. The sequence of choices of the penalty taker is generated by a stochastic chain with memory of variable length. It has been conjectured that the probability distribution of the response times is a function of the specific sequence of past choices governing the algorithm used by the penalty taker to make his choice at each step. We found empirical evidence that besides this dependence, the distribution of the response times depends also on the success or failure of the previous prediction made by the participant. Moreover, we found statistical evidence that this dependence propagates up to two steps forward after the prediction failure.

Effect of muscle length in a handgrip task on corticomotor excitability of extrinsic and intrinsic hand muscles under resting and submaximal contraction conditions

The neurophysiological mechanisms underlying muscle force control for different wrist postures still need to be better understood. To further elucidate these mechanisms, the present study aimed to investigate the effects of wrist posture on the corticospinal excitability by transcranial magnetic stimulation (TMS) of extrinsic (flexor [FCR] and extensor carpi radialis [ECR]) and intrinsic (flexor pollicis brevis (FPB)) muscles at rest and during a submaximal handgrip strength task. Fourteen subjects (24.06 ± 2.28 years) without neurological or motor disorders were included. We assessed how the wrist posture (neutral: 0°; flexed: +45°; extended: -45°) affects maximal handgrip strength (HGSmax ) and the motor evoked potentials (MEP) amplitudes during rest and active muscle contractions. HGSmax was higher at 0° (133%) than at -45° (93.6%; p < 0.001) and +45° (73.9%; p < 0.001). MEP amplitudes were higher for the FCR at +45° (83.6%) than at -45° (45.2%; p = 0.019) and at +45° (156%; p < 0.001) and 0° (146%; p = 0.014) than at -45° (106%) at rest and active condition, respectively. Regarding the ECR, the MEP amplitudes were higher at -45° (113%) than at +45° (60.8%; p < 0.001) and 0° (72.6%; p = 0.008), and at -45° (138%) than +45° (96.7%; p = 0.007) also at rest and active conditions, respectively. In contrast, the FPB did not reveal any difference among wrist postures and conditions. Although extrinsic and intrinsic hand muscles exhibit overlapping cortical representations and partially share the same innervation, they can be modulated differently depending on the biomechanical constraints.

Plasticity of face-hand sensorimotor circuits after a traumatic brachial plexus injury

Background

Interactions between the somatosensory and motor cortices are of fundamental importance for motor control. Although physically distant, face and hand representations are side by side in the sensorimotor cortex and interact functionally. Traumatic brachial plexus injury (TBPI) interferes with upper limb sensorimotor function, causes bilateral cortical reorganization, and is associated with chronic pain. Thus, TBPI may affect sensorimotor interactions between face and hand representations.

Objective

The aim of this study was to investigate changes in hand-hand and face-hand sensorimotor integration in TBPI patients using an afferent inhibition (AI) paradigm.

Method

The experimental design consisted of electrical stimulation (ES) applied to the hand or face followed by transcranial magnetic stimulation (TMS) to the primary motor cortex to activate a hand muscle representation. In the AI paradigm, the motor evoked potential (MEP) in a target muscle is significantly reduced when preceded by an ES at short-latency (SAI) or long-latency (LAI) interstimulus intervals. We tested 18 healthy adults (control group, CG), evaluated on the dominant upper limb, and nine TBPI patients, evaluated on the injured or the uninjured limb. A detailed clinical evaluation complemented the physiological investigation.

Results

Although hand-hand SAI was present in both the CG and the TBPI groups, hand-hand LAI was present in the CG only. Moreover, less AI was observed in TBPI patients than the CG both for face-hand SAI and LAI.

Conclusion

Our results indicate that sensorimotor integration involving both hand and face sensorimotor representations is affected by TBPI.

Reorganization of thalamocortical connections in congenitally blind humans

Cross-modal plasticity in blind individuals has been reported over the past decades showing that nonvisual information is carried and processed by "visual" brain structures. However, despite multiple efforts, the structural underpinnings of cross-modal plasticity in congenitally blind individuals remain unclear. We mapped thalamocortical connectivity and assessed the integrity of white matter of 10 congenitally blind individuals and 10 sighted controls. We hypothesized an aberrant thalamocortical pattern of connectivity taking place in the absence of visual stimuli from birth as a potential mechanism of cross-modal plasticity. In addition to the impaired microstructure of visual white matter bundles, we observed structural connectivity changes between the thalamus and occipital and temporal cortices. Specifically, the thalamic territory dedicated to connections with the occipital cortex was smaller and displayed weaker connectivity in congenitally blind individuals, whereas those connecting with the temporal cortex showed greater volume and increased connectivity. The abnormal pattern of thalamocortical connectivity included the lateral and medial geniculate nuclei and the pulvinar nucleus. For the first time in humans, a remapping of structural thalamocortical connections involving both unimodal and multimodal thalamic nuclei has been demonstrated, shedding light on the possible mechanisms of cross-modal plasticity in humans. The present findings may help understand the functional adaptations commonly observed in congenitally blind individuals.

Upper limb joint coordination preserves hand kinematics after a traumatic brachial plexus injury

Background

Traumatic brachial plexus injury (TBPI) causes a sensorimotor deficit in upper limb (UL) movements.

Objective

Our aim was to investigate the arm–forearm coordination of both the injured and uninjured UL of TBPI subjects.

Methods

TBPI participants (n = 13) and controls (n = 10) matched in age, gender, and anthropometric characteristics were recruited. Kinematics from the shoulder, elbow, wrist, and index finger markers were collected, while upstanding participants transported a cup to their mouth and returned the UL to a starting position. The UL coordination was measured through the relative phase (RP) between arm and forearm phase angles and analyzed as a function of the hand kinematics.

Results

For all participants, the hand transport had a shorter time to peak velocity (p &lt; 0.01) compared to the return. Also, for the control and the uninjured TBPI UL, the RP showed a coordination pattern that favored forearm movements in the peak velocity of the transport phase (p &lt; 0.001). TBPI participants' injured UL showed a longer movement duration in comparison to controls (p &lt; 0.05), but no differences in peak velocity, time to peak velocity, and trajectory length, indicating preserved hand kinematics. The RP of the injured UL revealed altered coordination in favor of arm movements compared to controls and the uninjured UL (p &lt; 0.001). Finally, TBPI participants' uninjured UL showed altered control of arm and forearm phase angles during the deceleration of hand movements compared to controls (p &lt; 0.05).

Conclusion

These results suggest that UL coordination is reorganized after a TBPI so as to preserve hand kinematics.

Visuo-Motor Affective Interplay: Bonding Scenes Promote Implicit Motor Pre-dispositions Associated With Social Grooming-A Pilot Study

Proximity and interpersonal contact are prominent components of social connection. Giving affective touch to others is fundamental for human bonding. This brief report presents preliminary results from a pilot study. It explores if exposure to bonding scenes impacts the activity of specific muscles related to physical interaction. Fingers flexion is a very important component when performing most actions of affectionate contact. We explored the visuo-motor affective interplay by priming participants with bonding scenes and assessing the electromyographic activity of the fingers flexor muscle, in the absence of any overt movements. Photographs of dyads in social interaction and of the same dyads not interacting were employed. We examined the effects upon the electromyographical activity: (i) during the passive exposure to pictures, and (ii) during picture offset and when expecting the signal to perform a fingers flexion task. Interacting dyads compared to matched non-interacting dyads increased electromyographic activity of the fingers flexor muscle in both contexts. Specific capture of visual bonding cues at the level of visual cortex had been described in the literature. Here we showed that the neural processing of visual bonding cues reaches the fingers flexor muscle. Besides, previous visualization of bonding cues enhanced background electromyographic activity during motor preparation to perform the fingers flexion task, which might reflect a sustained leakage of central motor activity downstream leading to increase in firing of the respective motor neurons. These data suggest, at the effector level, an implicit visuo-motor connection in which social interaction cues evoke intrinsic dispositions toward affectionate social behavior.

The Neuroscience Experiments System (NES)-A Software Tool to Manage Experimental Data and Its Provenance

Computational tools can transform the manner by which neuroscientists perform their experiments. More than helping researchers to manage the complexity of experimental data, these tools can increase the value of experiments by enabling reproducibility and supporting the sharing and reuse of data. Despite the remarkable advances made in the Neuroinformatics field in recent years, there is still a lack of open-source computational tools to cope with the heterogeneity and volume of neuroscientific data and the related metadata that needs to be collected during an experiment and stored for posterior analysis. In this work, we present the Neuroscience Experiments System (NES), a free software to assist researchers in data collecting routines of clinical, electrophysiological, and behavioral experiments. NES enables researchers to efficiently perform the management of their experimental data in a secure and user-friendly environment, providing a unified repository for the experimental data of an entire research group. Furthermore, its modular software architecture is aligned with several initiatives of the neuroscience community and promotes standardized data formats for experiments and analysis reporting.

Kinematic Changes in the Uninjured Limb After a Traumatic Brachial Plexus Injury

Background: Traumatic brachial plexus injury (TBPI) typically causes sensory, motor and autonomic deficits of the affected upper limb. Recent studies have suggested that a unilateral TBPI can also affect the cortical representations associated to the uninjured limb.

Objective: To investigate the kinematic features of the uninjured upper limb in participants with TBPI.

Methods: Eleven participants with unilateral TBPI and twelve healthy controls matched in gender, age and anthropometric characteristics were recruited. Kinematic parameters collected from the index finger marker were measured while participants performed a free-endpoint whole-body reaching task and a cup-to-mouth task with the uninjured upper limb in a standing position.

Results: For the whole-body reaching task, lower time to peak velocity (p = 0.01), lower peak of velocity (p = 0.003), greater movement duration (p = 0.04) and shorter trajectory length (p = 0.01) were observed in the TBPI group compared to the control group. For the cup-to-mouth task, only a lower time to peak velocity was found for the TBPI group compared to the control group (p = 0.02). Interestingly, no differences between groups were observed for the finger endpoint height parameter in either of the tasks. Taken together, these results suggest that TBPI leads to a higher cost for motor planning when it comes to movements of the uninjured limb as compared to healthy participants. This cost is even higher in a task with a greater postural balance challenge.

Conclusion: This study expands the current knowledge on bilateral sensorimotor alterations after unilateral TBPI and should guide rehabilitation after a peripheral injury.

Cerebellar damage affects the inference of human motion

The present study aims at the cerebellum's role in prediction mechanisms triggered by action observation. Five cerebellar patients and six age-paired control subjects were asked to estimate the occluded end point position of the shoulder's trajectories in Sit-to-Stand (STS) or Back-to-Sit (BTS) conditions, following or not biological rules. Contrarily to the control group, the prediction accuracy of the end point position in cerebellar patients did not depend on biological rules. Interestingly, both groups presented similar results when estimating the vanishing position of the target. Taken together, these results suggest that cerebellar damage affectsthe capacity of predicting upcoming actions by observation.

Retrieving the structure of probabilistic sequences of auditory stimuli from EEG data

Using a new probabilistic approach we model the relationship between sequences of auditory stimuli generated by stochastic chains and the electroencephalographic (EEG) data acquired while 19 participants were exposed to those stimuli. The structure of the chains generating the stimuli are characterized by rooted and labeled trees whose leaves, henceforth called contexts, represent the sequences of past stimuli governing the choice of the next stimulus. A classical conjecture claims that the brain assigns probabilistic models to samples of stimuli. If this is true, then the context tree generating the sequence of stimuli should be encoded in the brain activity. Using an innovative statistical procedure we show that this context tree can effectively be extracted from the EEG data, thus giving support to the classical conjecture.

Unilateral Brachial Plexus Lesion Impairs Bilateral Touch Threshold

Unilateral brachial plexus injury (BPI) impairs sensory and motor functions of the upper limb. This study aimed to map in detail brachial plexus sensory impairment both in the injured and the uninjured upper limb. Touch sensation was measured through Semmes-Weinstein monofilaments at the autonomous regions of the brachial plexus nerves, hereafter called points of exclusive innervation (PEIs). Seventeen BPI patients (31.35 years±6.9 SD) and 14 age-matched healthy controls (27.57 years±5.8 SD) were tested bilaterally at six selected PEIs (axillary, musculocutaneous, median, radial, ulnar, and medial antebrachial cutaneous [MABC]). As expected, the comparison between the control group and the brachial plexus patients' injured limb showed a robust difference for all PEIs (p ≤ 0.001). Moreover, the comparison between the control group and the brachial plexus uninjured limb revealed a difference for the median (p = 0.0074), radial (p = 0.0185), ulnar (p = 0.0404), and MABC (p = 0.0328) PEIs. After splitting the sample into two groups with respect to the dominance of the injured limb, higher threshold values were found for the uninjured side when it occurred in the right dominant limb compared to the control group at the median (p = 0.0456), radial (p = 0.0096), and MABC (p = 0.0078) PEIs. This effect was absent for the left, non-dominant arm. To assess the effect of the severity of sensory deficits observed in the injured limb upon the alterations of the uninjured limb, a K-means clustering algorithm (k = 2) was applied resulting in two groups with less or more severe sensory impairment. The less severely affected patients presented higher thresholds at the median (p = 0.0189), radial (p = 0.0081), ulnar (p = 0.0253), and MABC (p = 0.0187) PEIs in the uninjured limb in comparison with the control group, whereas higher thresholds at the uninjured limb were found only for the median PEI (p = 0.0457) in the more severely affected group. In conclusion, an expressive reduction in touch threshold was found for the injured limb allowing a precise mapping of the impairment caused by the BPI. Crucially, BPI also led to reduced tactile threshold in specific PEIs in the uninjured upper limb. These new findings suggest a superordinate model of representational plasticity occurring bilaterally in the brain after a unilateral peripheral injury.

Widespread white matter microstructural differences in schizophrenia across 4322 individuals: results from the ENIGMA Schizophrenia DTI Working Group

The regional distribution of white matter (WM) abnormalities in schizophrenia remains poorly understood, and reported disease effects on the brain vary widely between studies. In an effort to identify commonalities across studies, we perform what we believe is the first ever large-scale coordinated study of WM microstructural differences in schizophrenia. Our analysis consisted of 2359 healthy controls and 1963 schizophrenia patients from 29 independent international studies; we harmonized the processing and statistical analyses of diffusion tensor imaging (DTI) data across sites and meta-analyzed effects across studies. Significant reductions in fractional anisotropy (FA) in schizophrenia patients were widespread, and detected in 20 of 25 regions of interest within a WM skeleton representing all major WM fasciculi. Effect sizes varied by region, peaking at (d=0.42) for the entire WM skeleton, driven more by peripheral areas as opposed to the core WM where regions of interest were defined. The anterior corona radiata (d=0.40) and corpus callosum (d=0.39), specifically its body (d=0.39) and genu (d=0.37), showed greatest effects. Significant decreases, to lesser degrees, were observed in almost all regions analyzed. Larger effect sizes were observed for FA than diffusivity measures; significantly higher mean and radial diffusivity was observed for schizophrenia patients compared with controls. No significant effects of age at onset of schizophrenia or medication dosage were detected. As the largest coordinated analysis of WM differences in a psychiatric disorder to date, the present study provides a robust profile of widespread WM abnormalities in schizophrenia patients worldwide. Interactive three-dimensional visualization of the results is available at www.enigma-viewer.org.

Cerebral Dynamics during the Observation of Point-Light Displays Depicting Postural Adjustments

Objective: As highly social creatures, human beings rely part of their skills of identifying, interpreting, and predicting the actions of others on the ability of perceiving biological motion. In the present study, we aim to investigate the electroencephalographic (EEG) cerebral dynamics involved in the coding of postural control and examine whether upright stance would be codified through the activation of the temporal-parietal cortical network classically enrolled in the coding of biological motion. Design: We registered the EEG activity of 12 volunteers while they passively watched point light displays (PLD) depicting quiet stable (QB) and an unstable (UB) postural situations and their respective scrambled controls (QS and US). In a pretest, 13 volunteers evaluated the level of stability of our two biological stimuli through a stability scale. Results: Contrasting QB vs. QS revealed a typical ERP difference in the right temporal-parietal region at an early 200-300 ms time window. Furthermore, when contrasting the two biological postural conditions, UB vs. QB, we found a higher positivity in the 400-600 ms time window for the UB condition in central-parietal electrodes, lateralized to the right hemisphere. Conclusions: These results suggest that PLDs depicting postural adjustments are coded in the brain as biological motion, and that their viewing recruit similar networks with those engaged in postural stability control. Additionally, higher order cognitive processes appear to be engaged in the identification of the postural instability level. Disentangling the EEG dynamics during the observation of postural adjustments could be very useful for further understanding the neural mechanisms underlying postural control.

Observing Grasping Actions Directed to Emotion-Laden Objects: Effects upon Corticospinal Excitability

The motor system is recruited whenever one executes an action as well as when one observes the same action being executed by others. Although it is well established that emotion modulates the motor system, the effect of observing other individuals acting in an emotional context is particularly elusive. The main aim of this study was to investigate the effect induced by the observation of grasping directed to emotion-laden objects upon corticospinal excitability (CSE). Participants classified video-clips depicting the right-hand of an actor grasping emotion-laden objects. Twenty video-clips differing in terms of valence but balanced in arousal level were selected. Motor evoked potentials (MEPs) were then recorded from the first dorsal interosseous using transcranial magnetic stimulation (TMS) while the participants observed the selected emotional video-clips. During the video-clip presentation, TMS pulses were randomly applied at one of two different time points of grasping: (1) maximum grip aperture, and (2) object contact time. CSE was higher during the observation of grasping directed to unpleasant objects compared to pleasant ones. These results indicate that when someone observes an action of grasping directed to emotion-laden objects, the effect of the object valence promotes a specific modulation over the motor system.

Reduced functional connectivity within the primary motor cortex of patients with brachial plexus injury

This study aims at the effects of traumatic brachial plexus lesion with root avulsions (BPA) upon the organization of the primary motor cortex (M1). Nine right-handed patients with a right BPA in whom an intercostal to musculocutaneous (ICN-MC) nerve transfer was performed had post-operative resting state fMRI scanning. The analysis of empirical functional correlations between neighboring voxels revealed faster correlation decay as a function of distance in the M1 region corresponding to the arm in BPA patients as compared to the control group. No differences between the two groups were found in the face area. We also investigated whether such larger decay in patients could be attributed to a gray matter diminution in M1. Structural imaging analysis showed no difference in gray matter density between groups. Our findings suggest that the faster decay in neighboring functional correlations without significant gray matter diminution in BPA patients could be related to a reduced activity in intrinsic horizontal connections in M1 responsible for upper limb motor synergies.

Motor planning of goal-directed action is tuned by the emotional valence of the stimulus: a kinematic study

The basic underpinnings of homeostatic behavior include interacting with positive items and avoiding negative ones. As the planning aspects of goal-directed actions can be inferred from their movement features, we investigated the kinematics of interacting with emotion-laden stimuli. Participants were instructed to grasp emotion-laden stimuli and bring them toward their bodies while the kinematics of their wrist movement was measured. The results showed that the time to peak velocity increased for bringing pleasant stimuli towards the body compared to unpleasant and neutral ones, suggesting higher easiness in undertaking the task with pleasant stimuli. Furthermore, bringing unpleasant stimuli towards the body increased movement time in comparison with both pleasant and neutral ones while the time to peak velocity for unpleasant stimuli was the same as for that of neutral stimuli. There was no change in the trajectory length among emotional categories. We conclude that during the “reach-to-grasp” and “bring-to-the-body” movements, the valence of the stimuli affects the temporal but not the spatial kinematic features of motion. To the best of our knowledge, we show for the first time that the kinematic features of a goal-directed action are tuned by the emotional valence of the stimuli.

Balance Impairments after Brachial Plexus Injury as Assessed through Clinical and Posturographic Evaluation

Objective: To investigate whether a sensorimotor deficit of the upper limb following a brachial plexus injury (BPI) affects the upright balance.

Design: Eleven patients with a unilateral BPI and 11 healthy subjects were recruited. The balance assessment included the Berg Balance Scale (BBS), the number of feet touches on the ground while performing a 60 s single-leg stance and posturographic assessment (eyes open and feet placed hip-width apart during a single 60 s trial). The body weight distribution (BWD) between the legs was estimated from the center of pressure (COP) lateral position. The COP variability was quantified in the anterior-posterior and lateral directions.

Results: BPI patients presented lower BBS scores (p = 0.048) and a higher frequency of feet touches during the single-leg stance (p = 0.042) compared with those of the healthy subjects. An asymmetric BWD toward the side opposite the affected arm was shown by 73% of BPI patients. Finally, higher COP variability was observed in BPI patients compared with healthy subjects for anterior-posterior (p = 0.020), but not for lateral direction (p = 0.818).

Conclusions: This study demonstrates that upper limb sensorimotor deficits following BPI affect body balance, serving as a warning for the clinical community about the need to prevent and treat the secondary outcomes of this condition.

Preparing to caress: a neural signature of social bonding

It is assumed that social bonds in humans have consequences for virtually all aspects of behavior. Social touch-based contact, particularly hand caressing, plays an important role in social bonding. Pre-programmed neural circuits likely support actions (or predispositions to act) toward caressing contacts. We searched for pre-set motor substrates toward caressing by exposing volunteers to bonding cues and having them gently stroke a very soft cloth, a caress-like movement. The bonding cues were pictures with interacting dyads and the control pictures presented non-interacting dyads. We focused on the readiness potential, an electroencephalographic marker of motor preparation that precedes movement execution. The amplitude of the readiness potential preceding the grasping of pleasant emotional-laden stimuli was previously shown to be reduced compared with neutral ones. Fingers flexor electromyography measured action output. The rationale here is that stroking the soft cloth when previously exposed to bonding cues, a compatible context, would result in smaller amplitudes of readiness potentials, as compared to the context with no such cues. Exposure to the bonding pictures increased subjective feelings of sociability and decreased feelings of isolation. Participants who more frequently engage in mutual caress/groom a "significant other" in daily life initiated the motor preparation earlier, reinforcing the caress-like nature of the task. As hypothesized, readiness potentials preceding the caressing of the soft cloth were significantly reduced under exposure to bonding as compared to control pictures. Furthermore, an increased fingers flexor electromyographic activity was identified under exposure to the former as compared to the latter pictures. The facilitatory effects are likely due to the recruitment of pre-set cortical motor repertoires related to caress-like movements, emphasizing the distinctiveness of neural signatures for caress-like movements.

Motor imagery modulation of body sway is task-dependent and relies on imagery ability

In this study we investigate to what extent the effects of motor imagery on postural sway are constrained by movement features and the subject's imagery ability. Twenty-three subjects were asked to imagine three movements using the kinesthetic modality: rising on tiptoes, whole-body forward reaching, and whole-body lateral reaching. After each task, subjects reported the level of imagery vividness and were subsequently grouped into a HIGH group (scores ≥3, “moderately intense” imagery) or a LOW group (scores ≤2, “mildly intense” imagery). An eyes closed trial was used as a control task. Center of gravity (COG) coordinates were collected, along with surface EMG of the deltoid (medial and anterior portion) and lateral gastrocnemius muscles. COG variability was quantified as the amount of fluctuations in position and velocity in the forward-backward and lateral directions. Changes in COG variability during motor imagery were observed only for the HIGH group. COG variability in the forward-backward direction was increased during the rising on tiptoes imagery, compared with the control task (p = 0.01) and the lateral reaching imagery (p = 0.02). Conversely, COG variability in the lateral direction was higher in rising on tiptoes and lateral reaching imagery than during the control task (p < 0.01); in addition, COG variability was higher during the lateral reaching imagery than in the forward reaching imagery (p = 0.02). EMG analysis revealed no effects of group (p > 0.08) or task (p > 0.46) for any of the tested muscles. In summary, motor imagery influences body sway dynamics in a task-dependent manner, and relies on the subject' imagery ability.

Biological motion coding in the brain: analysis of visually driven EEG functional networks

Herein, we address the time evolution of brain functional networks computed from electroencephalographic activity driven by visual stimuli. We describe how these functional network signatures change in fast scale when confronted with point-light display stimuli depicting biological motion (BM) as opposed to scrambled motion (SM). Whereas global network measures (average path length, average clustering coefficient, and average betweenness) computed as a function of time did not discriminate between BM and SM, local node properties did. Comparing the network local measures of the BM condition with those of the SM condition, we found higher degree and betweenness values in the left frontal (F7) electrode, as well as a higher clustering coefficient in the right occipital (O2) electrode, for the SM condition. Conversely, for the BM condition, we found higher degree values in central parietal (Pz) electrode and a higher clustering coefficient in the left parietal (P3) electrode. These results are discussed in the context of the brain networks involved in encoding BM versus SM.

Perspective-taking in blindness: electrophysiological evidence of altered action representations

It is well established that the mental simulation of actions involves visual and/or somatomotor representations of those imagined actions. To investigate whether the total absence of vision affects the brain activity associated with the retrieval of motor representations, we recorded the readiness potential (RP), a marker of motor preparation preceding the execution, as well as the motor imagery of the right middle-finger extension in the first-person (1P; imagining oneself performing the movement) and in the third-person (3P; imagining the experimenter performing the movement) modes in 19 sighted and 10 congenitally blind subjects. Our main result was found for the single RP slope values at the Cz channel (likely corresponding to the supplementary motor area). No difference in RP slope was found between 1P and 3P in the sighted group, suggesting that similar motor preparation networks are recruited to simulate our own and other people's actions in spite of explicit instructions to perform the task in 1P or 3P. Conversely, reduced RP slopes in 3P compared with 1P found in the blind group indicated that they might have used an alternative, nonmotor strategy to perform the task in 3P. Moreover, movement imagery ability, assessed both by means of mental chronometry and a modified version of the Movement Imagery Questionnaire-Revised, indicated that blind and sighted individuals had similar motor imagery performance. Taken together, these results suggest that complete visual loss early in life modifies the brain networks that associate with others' action representations.

Electrophysiological correlates of biological motion permanence in humans

Spatiotemporal discontinuity of visual input is a common occurrence in daily life. For example, when a walking person disappears temporarily behind a wall, observers have a clear sense of his physical presence despite the absence of any visual information (movement permanence). To investigate the neural substrates of biological motion permanence, we recorded scalp EEG activity of sixteen subjects while they passively observed either biological or scrambled motion disappearing behind an occluder and reappearing. The moment of the occluder's appearance was either fixed or randomized. The statistical comparison between the biological and scrambled motion ERP waveforms revealed a modulation of activity in centro-parietal and right occipito-temporal regions during the occlusion phase when the biological motion disappearance was time-locked, possibly reflecting the recall of sensorimotor representations. These representations might allow the prediction of moving organisms in occlusion conditions. When the appearance of the occluder was unpredictable there was no difference between biological and scrambled motion either before or during occlusion, indicating that temporal prediction is relevant to the processing of biological motion permanence.

Semi-automatic measurement of visual verticality perception in humans reveals a new category of visual field dependency

Previous assessment of verticality by means of rod and rod and frame tests indicated that human subjects can be more (field dependent) or less (field independent) influenced by a frame placed around a tilted rod. In the present study we propose a new approach to these tests. The judgment of visual verticality (rod test) was evaluated in 50 young subjects (28 males, ranging in age from 20 to 27 years) by randomly projecting a luminous rod tilted between -18 and +18° (negative values indicating left tilts) onto a tangent screen. In the rod and frame test the rod was displayed within a luminous fixed frame tilted at +18 or -18°. Subjects were instructed to verbally indicate the rod's inclination direction (forced choice). Visual dependency was estimated by means of a Visual Index calculated from rod and rod and frame test values. Based on this index, volunteers were classified as field dependent, intermediate and field independent. A fourth category was created within the field-independent subjects for whom the amount of correct guesses in the rod and frame test exceeded that of the rod test, thus indicating improved performance when a surrounding frame was present. In conclusion, the combined use of subjective visual vertical and the rod and frame test provides a specific and reliable form of evaluation of verticality in healthy subjects and might be of use to probe changes in brain function after central or peripheral lesions.

Vision without Proprioception Modulates Cortico-spinal Excitability during Hand Motor Imagery

Several studies have shown a cortico-spinal facilitation during motor imagery. This facilitation effect is weaker when the actual hand posture is incompatible with the imagined movement. To determine whether the source of this interference effect arises from online proprioceptive information, we examined transcranial magnetic stimulation (TMS)-induced motor-evoked potentials during motor imagery in the deafferented subject G.L. The patient and 7 control subjects were asked to close their eyes and imagine joining the tips of the thumb and the little finger while maintaining a hand posture compatible or incompatible with the imagined movement. Contrary to control subjects' performance, G.L.'s results show that the facilitation observed during motor imagery was independent of the hand posture. To examine how vision of the hand interacts with the imagery process, G.L. and control subjects performed the same task with the eyes open. Like control subjects, when G.L. looked at her hand, a greater facilitation was observed when her hand posture was compatible with the imagined movement than when it was incompatible. These results suggest that in the absence of proprioception, vision may facilitate or inhibit motor representations and support the idea that limb position in the brain is organized around multisensory representations.

Mapping phantom movement representations in the motor cortex of amputees

Limb amputation results in plasticity of connections between the brain and muscles, with the cortical motor representation of the missing limb seemingly shrinking, to the presumed benefit of remaining body parts that have cortical representations adjacent to the now-missing limb. Surprisingly, the corresponding perceptual representation does not suffer a similar fate but instead persists as a phantom limb endowed with sensory and motor qualities. How can cortical reorganization after amputation be reconciled with the maintenance of a motor representation of the phantom limb in the brain? In an attempt to answer this question we explored the relationship between the cortical representation of the remaining arm muscles and that of phantom movements. Using transcranial magnetic stimulation (TMS) we systematically mapped phantom movement perceptions while simultaneously recording stump muscle activity in three above-elbow amputees. TMS elicited sensations of movement in the phantom hand when applied over the presumed hand area of the motor cortex. In one subject the amplitude of the perceived movement was positively correlated with the intensity of stimulation. Interestingly, phantom limb movements that the patient could not produce voluntarily were easily triggered by TMS, suggesting that the inability to voluntarily move the phantom is not equivalent to a loss of the corresponding movement representation. We suggest that hand movement representations survive in the reorganized motor area of amputees even when these cannot be directly accessed. The activation of these representations is probably necessary for the experience of phantom movement.

A freezing-like posture to pictures of mutilation

Postural sway and heart rate were recorded in young men viewing emotionally engaging pictures. It was hypothesized that they would show a human analog of "freezing" behavior (i.e., immobility and heart rate deceleration) when confronted with a sustained block of unpleasant (mutilation) images, relative to their response to pleasant/arousing (sport action) or neutral (objects) pictures. Volunteers stood on a stabilometric platform during picture viewing. Significantly reduced body sway was recorded during the unpleasant pictures, along with increased mean power frequency (indexing muscle stiffness). Heart rate during unpleasant pictures also showed the expected greater deceleration. This pattern resembles the "freezing" and "fear bradycardia" seen in many species when confronted with threatening stimuli, mediated by neural circuits that promote defensive survival.

The Influence of Hand Posture on Corticospinal Excitability during Motor Imagery: A Transcranial Magnetic Stimulation Study

In order to study the interaction between proprioceptive information and motor imagery, we herein investigate how compatible and incompatible postural signals influence corticospinal excitability during the mental simulation of hand movements. Subjects were asked to imagine themselves joining the tips of the thumb and the little finger while they maintained one of the two following hand postures: posture A (PA, compatible), little finger, index and thumb extended, the remaining fingers flexed; or posture B (PB, incompatible), index and thumb extended, other fingers flexed. All subjects rated the imagined finger opposition movements as easier to perform when the hand was kept in PA than in PB (P < 0.01) and the correlation between the duration of motor imagery and movement execution was also higher for PA than PB (P < 0.01). For each posture, motor evoked potentials (MEPs) elicited by focal transcranial magnetic stimulation (TMS) of the left motor cortex were recorded from the right opponens pollicis muscle during both motor imagery (MI) and rest (R) conditions. MEP area varied according to the hand posture: PA induced a higher increase in corticospinal excitability, when compared with PB. These results indicate that the actual limb posture affects the process of motor imagery. The source of this postural modulation effect is discussed.

Light-induced Egr-1 expression in the striate cortex of the opossum

In the present study, immunocytochemistry was used to assess the expression of Egr-1 nuclear protein across selected regions of the opossum visual system. In light-deprived (LD) animals, only a few scattered cell nuclei were found throughout the striate cortex (V1). Exposure to light promoted a significant increase in the density of Egr-1 labeled nuclei in V1. Laminar distribution of immunoreactive nuclei in light-stimulated animals (LS) tended to vary with topography: the lateral region, which corresponds to the central representation of the visual field, appeared to have higher density of cells expressing protein in the supragranular layers, as compared to the medial region, which corresponds to the representation of the peripheral field of vision. Finally, LS animals displayed a narrow band of labeled cell nuclei in the intergeniculate leaflet (IGL) and throughout the anteroposterior extent of the superior colliculus (SC). In contrast, almost no Egr-1 immunolabeling was found in the IGL and SC of LD animals. Our report is the first demonstration of light-regulated expression of the Egr-1 gene in the opossum visual system and provides evidence that the expression of an activity-dependent gene related to neural plasticity is evolutionarily conserved in the visual cortex of the mammalian lineage.

The brain decade in debate: VI. Sensory and motor maps: dynamics and plasticity

This article is an edited transcription of a virtual symposium promoted by the Brazilian Society of Neuroscience and Behavior (SBNeC). Although the dynamics of sensory and motor representations have been one of the most studied features of the central nervous system, the actual mechanisms of brain plasticity that underlie the dynamic nature of sensory and motor maps are not entirely unraveled. Our discussion began with the notion that the processing of sensory information depends on many different cortical areas. Some of them are arranged topographically and others have non-topographic (analytical) properties. Besides a sensory component, every cortical area has an efferent output that can be mapped and can influence motor behavior. Although new behaviors might be related to modifications of the sensory or motor representations in a given cortical area, they can also be the result of the acquired ability to make new associations between specific sensory cues and certain movements, a type of learning known as conditioning motor learning. Many types of learning are directly related to the emotional or cognitive context in which a new behavior is acquired. This has been demonstrated by paradigms in which the receptive field properties of cortical neurons are modified when an animal is engaged in a given discrimination task or when a triggering feature is paired with an aversive stimulus. The role of the cholinergic input from the nucleus basalis to the neocortex was also highlighted as one important component of the circuits responsible for the context-dependent changes that can be induced in cortical maps.

Metabolic changes in the nucleus of the optic tract after monocular enucleation as revealed by cytochrome oxidase histochemistry

The histochemistry for the mitochondrial enzyme cytochrome oxidase (CO) was used to evaluate the levels of metabolic activity in neurons of the nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) in the opossum (Didelphis aurita). The observations were performed in four groups: normal juveniles (4 months old), monocularly enucleated juveniles analysed when adults, normal adults (8 to 18 months old) and monocularly enucleated adults. CO labeled cells were observed to have a similar distribution along the NOT-DTN anteroposterior axis in both juvenile and adult normal animals. Monocular enucleation performed in adults produced a significant reduction of the reactive neuropil but not of the number of CO labeled cells in the deafferented NOT-DTN: the number of labeled neurons per section in the deafferented side matched those of the ipsilateral complex. In juveniles, however, this procedure caused a systematic reduction of the number of CO labeled cells in the contralateral NOT-DTN in comparison to the spared complex. The lack of reduction in the number of neurons found on the deafferented side of the NOT-DTN of monocularly enucleated adult opossums compared with the ipsilateral side might result from the presence of compensatory inputs to maintain their metabolic equivalence. However, when the monocular enucleation was performed in juvenile opossums, a statistically significant asymmetry of CO neurons in the NOT-DTN was observed. In other words, the compensatory mechanisms proposed for the adults were either absent or insufficient to achieve symmetry in juveniles, suggesting a more heavily reliance in the retinal input.

Cortical and subcortical influences on the nucleus of the optic tract of the opossum

In the present work we propose a new phylogenetic hypothesis for the role played by cortical and subcortical afferents to the nucleus of the optical tract, the main visual relay station of the horizontal optokinetic reflex in mammals. The hypothesis is supported by anatomical and physiological data obtained in the South American opossum (Didelphis aurita) using the following experimental approaches: (i) single-unit recordings in the nucleus of the optic tract and simultaneous electrical stimulation of the contralateral nucleus of the optic tract; (ii) single-unit recordings in the nucleus of the optic tract and simultaneous electrical stimulation of the ipsilateral striate cortex; (iii) injection of cholera toxin subunit B into the striate cortex and subsequent immunohistochemical reaction to reveal the presence of the marker in the thalamus and mesencephalon; and (iv) single-unit recordings in the nucleus of the optic tract both before and after ablation of the ipsilateral visual cortex. The main results are: (i) there is a strong inhibitory reciprocal effect upon the nucleus of the optic tract following stimulation of its contralateral counterpart; (ii) electrophysiological and anatomical data imply that the visual cortex does not project directly to the nucleus of the optic tract. Rather, cortical terminals seem to target the nearby anterior and posterior pretectal nuclei and orthodromic latencies in the nucleus of the optic tract following stimulation of the visual cortex were twice as large as in the superior colicullus; and (iii) ablation of the entire visual cortex did not have any effect upon binocularity of cells in the nucleus of the optic tract. These results strengthen the model proposed here for the role of the interactions between the nuclei of the optic tract under optokinetic stimulation. The hypothesis in the present work is that the cortical influences upon the nucleus of the optical tract, in addition to the subcortical ones, appeared only recently in phylogenesis. In more primitive mammals, such as the opossum, subcortical interactions are thought to play a relatively important role. With the emergence of retinal specializations, such as the fovea, one might suppose that there followed the appearance of new ocular movements, such as the smooth pursuit and certain types of saccades, that came to join the pre-existent optokinetic reflex.

Cytochrome oxidase and NADPH-diaphorase on the afferent relay branch of the optokinetic reflex in the opossum

In the present study, histochemical techniques combined with more conventional anatomical methods were used to refine the identification of the nucleus of the optic tract and the nuclei of the accessory optic system in the opossum. The distribution of the enzyme cytochrome oxidase (CO) was examined in the cells and the neuropil of the opossum's mesodiencephalic region. Strong CO labeling was present in the nucleus of the optic tract (NOT)-dorsal terminal nucleus (DTN). Alternate sections, taken from animals that had received bilateral injections of horseradish peroxidase centered in the region of the inferior olive, were subjected to assays for CO and horseradish peroxidase. The region occupied by CO-labeled cells in the NOT-DTN superimposed with the one defined by retrogradely labeled cells. Cell counts along the NOT-DTN anteroposterior axis revealed that although the olivary and CO-positive cells were confined within similar boundaries, the latter are up to twofold more numerous than the former. As revealed by cytochrome oxidase histochemistry, the outlines of the NOT-DTN, the other pretectal nuclei and the nuclei belonging to the accessory optic system coincided with those revealed by the histochemistry for nicotinamide dinucleotide phosphate diaphorase (NADPH-d). After an intraocular injection of cholera toxin beta subunit and alternate sections processing for NADPH-d and CO, the distribution of labeled retinal terminal fields in the mesodiencephalic region was shown to be coincident with regions of high levels of histochemical labeling. These results are discussed in the light of previous anatomofunctional assessments of the pretectum and accessory optic system.

On the functional anatomy of the nucleus of the optic tract-dorsal terminal nucleus commissural connection in the opossum (Didelphis marsupialis aurita)

Immunocytochemical methods revealed the presence of GABA in cell bodies and terminals in the nucleus of the optic tract-dorsal terminal nucleus, the medial terminal nucleus, the lateral terminal nucleus and the interstitial nucleus of the superior fasciculus of the opossum (Didelphis marsupialis aurita). Moreover, after unilateral injections of rhodamine beads in the nucleus of the optic tract-dorsal terminal nucleus complex and processing for GABA, double-labelled cells were detected in the ipsilateral complex, up to 400 microns from the injected site, but not in the opposite. Analysis of the distributions of GABAergic and retrogradely-labelled cells throughout the contralateral nucleus of the optic tract-dorsal terminal nucleus showed that the highest density of GABAergic and rhodamine-labelled cells overlapped at the middle third of the complex. Previous electrophysiological data obtained in the opossum had suggested the existence, under certain conditions, of an inhibitory action between the nucleus of the optic tract-dorsal terminal nucleus of one side over the other. The absence of GABAergic commissural neurons may imply that this inhibition is mediated by an excitatory commissural pathway that activates GABAergic interneurons.

The nucleus of the optic tract of the opossum

This paper reviews anatomical and electrophysiological data on the nucleus of the optic tract (NOT) of the opossum, a nucleus in the afferent branch of the horizontal optokinetic reflex. It is proposed that subcortical routes are essential for responses from the two eyes: a direct retinal projection from the contralateral eye and a commissural pathway between the two NOTs for the ipsolateral eye. In the latter case there's evidence that the commisural axons have a relay on inhibitory neurones. This circuit accounts for the differences in response pattern under monocular condition: temporo-nasal motion of the visual stimulus elicits excitation in the contralateral NOT, resulting in inhibition of the ipsolateral nucleus, while naso-temporal motion promotes inhibition in the contralateral nucleus, releasing the ipsolateral nucleus from the commissural input.

The nucleus of the optic tract (NOT) and the dorsal terminal nucleus (DTN) of opossums (Didelphis marsupialis aurita)

Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was injected unilaterally into the pretectocollicular region of opossums (Didelphis marsupialis aurita), primarily to investigate the existence of a commissural subcortical pathway but also to reveal afferents and efferents of the nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) in this species. Labelled cells and terminals were observed in the contralateral NOT-DTN. Furthermore, HRP was injected bilaterally in the region of the inferior olive (IO) to verify if the distribution of labelled cells in the NOT-DTN overlapped the region of commissural labelled cells. The two subpopulations of retrogradely labelled cells coincided, being distributed within the retinal terminal field attributed to the NOT-DTN, as revealed by contralateral eye injections of HRP. The commissural cells were located slightly more ventral than the olivary cells in the optic tract. The pretectocollicular WGA-HRP injections also labelled cells and terminals bilaterally in the lateral terminal nucleus (LTN), interstitial nucleus of the superior fasciculus, posterior fibers (INSFp), ventral lateral geniculate nucleus (vLGN), and superior colliculus (SC) and ipsilaterally in the medial terminal nucleus (MTN). In addition, further caudally, labelled cells and terminals were observed bilaterally in the nuclei prepositus hypoglossi (PH) and in the medial (MVN) and lateral (LVN) vestibular nuclei. Labelled terminals were found in the ipsilateral nucleus reticularis tegmenti pontis (NRTP) and in the IO with ipsilateral predominance. This study allowed an anatomical delimitation of the NOT-DTN in this opossum species, as defined by the olivary and commissural subpopulations, as well as a hodological evaluation of this region. The existence of some common anatomical aspects with other mammalian species is discussed.