Biology subjects

Davare, M.

Publications and source records attributed to Davare, M..

17 recordsLinked to original sources

bioRxiv2022

The ExtRA Capacity Test: Reliability and validity study of a new tool for assessing shoulder muscle performance

ObjectivesThe primary objective was to evaluate the reliability of a new tool for assessing shoulder muscle performance: The ExtRA Capacity Test. The secondary objective was to assess whether this tool was a valid measure for assessing shoulder strength. MethodsThe ExtRA Capacity test involves two measures: maximal scapular plane lateral raises to 90{degrees} abduction with 2.5kg of external load and the maximal number of prone lying unsupported external rotations with the shoulder at 90{degrees} abduction. Both capacity tests are completed to a metronome set to 30 beats per minute 20 asymptomatic participants were sampled on 2 separate sessions, 1 week apart. The ExtRA Capacity Test was completed by the lead researcher and an independent physiotherapist. Shoulder strength was also measured using isokinetic dynamometry. ResultsThe test showed excellent inter-rater reliability (mean abduction ICC= 0.969, mean external rotation ICC= 0.822, with a 95% CI). Mean intra-rater variability was 3.96{+/-} 4.09 for the abduction measure and 1.70{+/-} 1.17 for the external rotation measure. Validity was calculated using Pearson correlation coefficient. The abduction measure showed good/ moderate correlation for the majority of strength measurements taken using isokinetic dynamometry however the external rotation capacity test did not correlate closely to isokinetic dynamometry strength measures. ConclusionThe abduction component of the ExtRA Capacity Test is a suitable measure for assessing shoulder strength in clinical practice. The external rotation measure is of suitable reliability however if used in clinical practice, it should not be used to assess shoulder strength, instead it may be suitable to assess movement control of the shoulder. SummaryVarious methods of measuring shoulder strength exist, ranging from cost free, relatively inaccurate methods to costly, complex methods which are of high reliability and validity but are challenging to use in a fast-pace, clinical environment. Objective outcome measures are used within a rehabilitation setting however at present there is no upper limb muscle performance test that is suitable to use on all people, regardless of strength or fitness level. Capacity testing of movements provides a functional, insight into strength specific to a real world/ sporting environment with lower limb capacity tests providing clear objective baselines that can be used for goal setting and providing return to play criteria following injury. This study proves the reliability and validity of the ExtRA Capacity Test which is a measure of shoulder muscle performance, suitable for people of all physical activity levels and upper limb strength.

physiology↗

bioRxiv2022

The effect of type and context of sensorimotor information on corticospinal excitability

Fingertip force scaling during hand-object interactions typically relies on visual information about the object and sensorimotor memories from previous object interactions. Here, we investigated whether contextual information, that is not explicitly linked to the intrinsic object properties (e.g., size or weight) but is informative for motor control requirements, can mediate force scaling. For this, we relied on two separate behavioral tasks during which we applied transcranial magnetic stimulation (TMS) to probe corticospinal excitability (CSE), as a window onto the primary motor cortex role in controlling fingertip forces. In experiment 1, participants performed a force tracking task, where we manipulated available implicit and explicit visual information. That is, either the force target was fully visible, or only the force error was displayed as a deviation from a horizontal line. We found that participants performance was better when the former condition, in which they had explicit access to predictive information. However, we did not find differences in CSE modulation based on the type of visual information. On the other hand, CSE was modulated by the change in muscle contraction, i.e., contraction vs. relaxation and fast vs. slow changes. In sum, these findings indicate that CSE only reflects the ongoing motor command. In experiment 2, other participants performed a sequential object lifting task of visually identical objects that were differently weighted, in a seemingly random order. Within this task, we hid short series of incrementally increasing object weights. This allowed us to investigate whether participants would scale their forces for specific object weights based on the previously lifted object (i.e., sensorimotor effect) or based on the implicit information about the hidden series of incrementally increasing weights (i.e., extrapolation beyond sensorimotor effects). Results showed that participants did not extrapolate fingertip forces based on the hidden series but scaled their forces solely on the previously lifted object. Unsurprisingly, CSE was not modulated differently when lifting series of random weights versus series of increasing weights. Altogether, these results in two different grasping tasks suggest that CSE encodes ongoing motor components but not sensorimotor cues that are hidden within contextual information. HighlightsO_LIExplicit visual cues and sensorimotor experience are key for object grasping C_LIO_LIInvestigating influence of implicit, contextual information on object grasping C_LIO_LIExplicit but not implicit cues improve motor performance during object grasping C_LIO_LIExplicit but not implicit cues modulate corticospinal excitability C_LI

neuroscience↗

bioRxiv2021

Prefrontal stimulation prior to motor sequence learning alters multivoxel patterns in the striatum and the hippocampus

Motor sequence learning (MSL) is supported by dynamical interactions between hippocampal and striatal networks that are thought to be orchestrated by the prefrontal cortex. In the present study, we tested whether individually-tailored theta-burst stimulation of the dorsolateral prefrontal cortex (DLPFC) prior to MSL, can modulate multivoxel response patterns in the stimulated cortical area, the hippocampus and the striatum. Response patterns were assessed with multivoxel correlation structure analyses of functional magnetic resonance imaging data acquired during task practice and during resting-state scans before and after learning/stimulation. Results revealed that, across stimulation conditions, MSL induced greater modulation of task-related DLPFC multivoxel patterns than random practice. A similar learning-related modulatory effect was observed on sensorimotor putamen patterns under inhibitory stimulation. Furthermore, MSL as well as inhibitory stimulation affected (posterior) hippocampal multivoxel patterns at post-intervention rest. Exploratory analyses showed that MSL-related brain patterns in the posterior hippocampus persisted into post-learning rest preferentially after inhibitory stimulation. These results collectively show that prefrontal stimulation can alter multivoxel brain patterns in deep brain regions that are critical for the MSL process. They also suggest that stimulation influenced early offline consolidation processes as evidenced by a stimulation-induced modulation of the reinstatement of task pattern into post-learning wakeful rest.

neuroscience↗

bioRxiv2020

Neural effects of continuous theta-burst stimulation in macaque parietal neurons

Theta-burst transcranial magnetic stimulation (TBS) has become a standard non-invasive technique to induce offline changes in cortical excitability in human volunteers. Yet, TBS suffers from a high variability across subjects. A better knowledge about how TBS affects neural activity in vivo could uncover its mechanisms of action and ultimately allow its mainstream use in basic science and clinical applications. To address this issue, we applied continuous TBS (cTBS, 300 pulses) in awake behaving rhesus monkeys and quantified its after-effects on neuronal recordings and behavior. Guided by anatomical MRI, we recorded single-cell activity in parietal area PFG during passive fixation of real-world objects. Overall, we observed a pronounced, long-lasting and highly reproducible reduction in neuronal excitability after cTBS in individual parietal neurons, with some neurons exhibiting periods of hyperexcitability during the recovery phase. We applied the same stimulation protocol during visually-guided grasping of objects, and observed a significant grasping impairment. These results provide the first experimental evidence on the effects of cTBS on single neurons in awake behaving monkeys.

neuroscience↗

bioRxiv2020

Motor resonance is modulated by an object's weight distribution

Transcranial magnetic stimulation (TMS) studies showed that corticospinal excitability (CSE) is modulated during observation of object lifting, an effect termed motor resonance. Specifically, motor resonance is driven by movement features indicating object weight, such as object size or observed movement kinematics. We investigated in 16 humans (8 females) whether motor resonance is also modulated by an objects weight distribution. Participants were asked to lift an inverted T-shaped manipulandum with interchangeable center of mass after first observing an actor lift the same manipulandum. Participants and actor were instructed to minimize object roll and rely on constrained digit positioning during lifting. Constrained positioning was either collinear (i.e., fingertips on the same height) or noncollinear (i.e., fingertip on the heavy side higher than the one on the light side). The center of mass changed unpredictably before the actors lifts and participants were explained that their weight distribution always matched the actors one. Last, TMS was applied during both lift observation and planning of lift actions. Our results showed that CSE was similarly modulated during lift observation and planning: when participants observed or planned lifts in which the weight distribution was asymmetrically right-sided, CSE recorded from the thumb muscles was significantly increased compared to when the weight distribution was left-sided. During both lift observation and planning, this increase seemed to be primarily driven by the weight distribution and not specifically by the (observed) digit positioning or muscle contraction. In conclusion, our results indicate that complex intrinsic object properties such as weight distributions can modulate activation of the motor system during both observation and planning of lifting actions. Highlights* Motor resonance is observation-induced activity in the observers motor system * We used a dyadic lifting task of objects with asymmetrical weight distribution * We investigated which movement features modulate motor resonance * Motor resonance is modulated by the objects weight distribution * Motor resonance is driven by observed and planned digit positioning

neuroscience↗

bioRxiv2020

Top-down contextual requirement to suppress self-movement influences grasp-specific modulation of corticospinal excitability during action observation

Action observation modulates corticospinal excitability (CSE) measured via transcranial magnetic stimulation (TMS) in humans, which presumably exposes the effect of mirror neuron activation on corticospinal pathways. These responses can consist of both facilitation and suppression, and the balance of these two may restrict the outflow of activity into movement. Evidence also suggests that task context can considerably influence CSE changes during action observation. Here, we assessed whether embedding action observation within a Go-NoGo paradigm, emphasizing movement withholding on observation and NoGo trials, influenced CSE modulation. Fourteen healthy subjects received single pulse TMS over left primary motor cortex (M1) during a baseline period, grasp observation onset, or after a NoGo cue, while performing, observing, or withholding two distinct reach-to-grasp actions. We assessed modulation of motor evoked potentials (MEPs) in three intrinsic hand muscles, which were recruited in a grasp-specific manner during action execution. CSE modulation was limited, and predominantly suppressive in nature during grasp observation. Seven subjects performed the same task without the NoGo condition ("Go-only" block) immediately before the "Go&NoGo" block. We found evidence for grasp-specific modulation of CSE, which matched the recruitment pattern of the muscles during action execution. Within these subjects, modulation was attenuated when the NoGo condition was introduced, but was still distinct from modulation in the first group. These results suggest that bottom-up grasp-specific modulation of MEPs during action observation is attenuated by the top-down contextual requirement to suppress self-movement, and facilitation and suppression effects are determined by the balance between these two processes. SIGNIFICANCE STATEMENTAction observation can activate specific pathways in the motor system of the observer, which are also used to perform the same action. This motor resonance, measured via changes in corticospinal excitability using transcranial magnetic stimulation, is susceptible to task context. In this study, we show that observing grasping actions results in grasp-specific changes in excitability, consistent with mirror neuron activation, but this effect is masked when observation is interleaved within a Go-NoGo paradigm, which emphasises suppression of ones own movement. Top-down task requirements to withhold movement within and across trials, which are present in most action observation studies, likely influence the extent of motor resonance, urging caution in the design and interpretation of results in TMS action observation experiments.

neuroscience↗

bioRxiv2020

Lift observation conveys object weight distribution but partly enhances predictive lift planning

Observation of object lifting allows updating of internal object representations for object weight, in turn enabling accurate scaling of fingertip forces when lifting the same object. Here, we investigated whether lift observation also enables updating of internal representations for an objects weight distribution. We asked participants to lift an inverted T-shaped manipulandum, of which the weight distribution could be changed, in turns with an actor. Participants were required to minimize object roll (i.e., lift performance) during lifting and were allowed to place their fingertips at self-chosen locations. The center of mass changed unpredictably every third to sixth trial performed by the actor and participants were informed that they would always lift the same weight distribution as the actor. Participants observed either erroneous (i.e., object rolling towards its heavy side) or skilled (i.e., minimized object roll) lifts. Lifting performance after observation was compared to lifts without prior observation and to lifts after active lifting, which provided haptic feedback about the weight distribution. Our results show that observing both skilled and erroneous lifts convey an objects weight distribution similar to active lifting, resulting in altered digit positioning strategies. However, minimizing object roll on novel weight distributions was only improved after observing error lifts and not after observing skilled lifts. In sum, these findings suggest that although observing motor errors and skilled motor performance enables updating of digit positioning strategy, only observing error lifts enables changes in predictive motor control when lifting objects with unexpected weight distributions. New and noteworthyIndividuals are able to extract an objects size and weight by observing interactions with objects and subsequently integrate this information in their own motor repertoire. Here, we show that this ability extrapolates to weight distributions. Specifically, we highlighted that individuals can perceive an objects weight distribution during lift observation but can only partially embody this information when planning their own actions.

neuroscience↗

bioRxiv2020

Hippocampal and striatal responses during motor learning are modulated byprefrontal cortex stimulation

While it is widely accepted that motor sequence learning (MSL) is supported by a prefrontal-mediated interaction between hippocampal and striatal networks, it remains unknown whether the functional responses of these networks can be modulated in humans with targeted experimental interventions. The present proof- of-concept study employed a comprehensive multimodal neuroimaging approach, including functional magnetic resonance (MR) imaging and MR spectroscopy, to investigate whether individually-tailored theta-burst stimulation of the dorsolateral prefrontal cortex can modulate responses in the hippocampus and striatum during motor learning. Our results indicate that stimulation influenced task-related connectivity patterns within hippocampo-frontal and striatal networks. Stimulation also altered the relationship between the levels of gamma-aminobutyric acid (GABA) in the stimulated prefrontal cortex and learning-related changes in both activity and connectivity in fronto-striato-hippocampal networks. This study provides the first experimental evidence that brain stimulation can alter motor learning-related functional responses in the striatum and hippocampus.

neuroscience↗

bioRxiv2020

Effects of TMS over the anterior intraparietal area on anticipatory fingertip force scaling and the size-weight illusion

In skilled object lifting, fingertip forces need to be carefully scaled to object weight, which can be inferred from object properties, such as size or material. This anticipatory force scaling ensures smooth and efficient lifting movements. However, even with accurate motor plans, weight perception can still be biased. In the size-weight illusion, objects of different size but equal weight are perceived to differ in heaviness, with the small object perceived to be heavier than the large object. The neural underpinnings of the size-weight illusion and anticipatory force scaling to object size are largely unknown. In this study, we hypothesized a possible role of the anterior intraparietal cortex (aIPS) in predictive force scaling and the size-weight illusion, which we investigated by applying continuous theta burst stimulation (cTBS) prior to participants lifting objects designed to induce the size-weight illusion. Participants received cTBS over aIPS, the primary motor cortex (control area), or sham stimulation. We found no evidence that aIPS stimulation affected the size-weight illusion. Small effects were, however, found on anticipatory force scaling, where grip force was less tuned to object size during initial lifts. These findings suggest that, while aIPS might be peripherally involved in sensorimotor prediction, other brain areas underpin the processes that mediate the size-weight illusion.

neuroscience↗

bioRxiv2019

The role of the anterior intraparietal sulcus and the lateral occipital cortex in fingertip force scaling and weight perception during object lifting

Skillful object lifting relies on scaling fingertip forces according to the objects weight. When no visual cues about weight are available, force planning relies on recent lifting experience. Recently, we showed that previously lifted objects also affect weight estimation, as objects are perceived to be lighter when lifted after heavy objects compared to light ones. Here, we investigated the underlying neural mechanisms mediating these effects. We asked participants to lift objects and estimate their weight. Simultaneously, we applied transcranial magnetic stimulation (TMS) during the dynamic loading or static holding phase. Two subject groups received TMS of either the anterior intraparietal sulcus (aIPS) or lateral occipital area (LO), known to be important nodes in object grasping and perception. We hypothesized that TMS-induced disruption of aIPS and LO would alter force scaling and weight perception. Contrary to our hypothesis, we did not find effects of aIPS or LO stimulation on force planning or weight estimation caused by previous lifting experience. However, we found that TMS of both areas increased grip forces, but only when applied during dynamic loading, and decreased weight estimation, but only when applied during static holding, suggesting time-specific effects. Interestingly, our results also indicate that TMS over LO, but not aIPS, affected load force scaling specifically for heavy objects, which further indicates that planning of load and grip forces might be controlled differently. These findings provide new insights on the interactions between brain networks mediating action and perception during object manipulation. NEW & NOTEWORTHYThis article provides new insights into the neural mechanisms underlying object lifting and perception. Using transcranial magnetic stimulation during object lifting, we show that effects of previous experience on force scaling and weight perception are not mediated by the anterior intraparietal sulcus nor the lateral occipital cortex (LO). In contrast, we highlight a unique role for LO in load force scaling, suggesting different brain processes for grip and load force scaling in object manipulation.

neuroscience↗

bioRxiv2019

Sensorimotor expectations bias motor resonance during observation of object lifting: The causal role of pSTS

Transcranial magnetic stimulation (TMS) studies have highlighted that corticospinal excitability (CSE) is increased during observation of object lifting, an effect termed motor resonance. This facilitation is driven by movement features indicative of object weight, such as object size or observed movement kinematics. Here, we investigated in 35 humans (23 females) how motor resonance is altered when the observers weight expectations, based on visual information, do not match the actual object weight as revealed by the observed movement kinematics. Our results highlight that motor resonance is not robustly driven by object weight but easily masked by a suppressive mechanism reflecting the correctness of the weight expectations. Subsequently, we investigated in 24 humans (14 females) whether this suppressive mechanism was driven by higher-order cortical areas. For this, we induced virtual lesions to either the posterior superior temporal sulcus (pSTS) or dorsolateral prefrontal cortex (DLPFC) prior to having participants perform the task. Importantly, virtual lesion of pSTS eradicated this suppressive mechanism and restored object weight-driven motor resonance. In addition, DLPFC virtual lesion eradicated any modulation of motor resonance. This indicates that motor resonance is heavily mediated by top-down inputs from both pSTS and DLPFC. Altogether, these findings shed new light on the theorized cortical network driving motor resonance. That is, our findings highlight that motor resonance is not only driven by the putative human mirror neuron network consisting of the primary motor and premotor cortices as well as the anterior intraparietal sulcus, but also by top-down input from pSTS and DLPFC. Significance StatementObservation of object lifting activates the observers motor system in a weight-specific fashion: Corticospinal excitability is larger when observing lifts of heavy objects compared to light ones. Interestingly, here we demonstrate that this weight-driven modulation of corticospinal excitability is easily suppressed by the observers expectations about object weight and that this suppression is mediated by the posterior superior temporal sulcus. Thus, our findings show that modulation of corticospinal excitability during observed object lifting is not robust but easily altered by top-down cognitive processes. Finally, our results also indicate how cortical inputs, originating remotely from motor pathways and processing action observation, overlap with bottom-up motor resonance effects.

neuroscience↗

bioRxiv2019

Mapping effective connectivity between the frontal and contralateral primary motor cortex using dual-coil transcranial magnetic stimulation

Cytoarchitectonic, anatomical and electrophysiological studies have divided the frontal cortex into distinct functional subdivisions. Many of these subdivisions are anatomically connected with the contralateral primary motor cortex (M1); however, effective neurophysiological connectivity between these regions is not well defined in humans. Therefore, we aimed to use dual-coil transcranial magnetic stimulation (TMS) to map, with high spatial resolution, the effective connectivity between different frontal regions of the right hemisphere and contralateral M1 (cM1). TMS was applied over the left M1 alone (test pulse) or after a conditioning pulse was applied to different grid points covering the right frontal cortex, while subjects were at rest, prepared an index finger abduction (Prep-ABD) or precision grip (Prep-PG). MEP motor maps were generated by creating synthetic fMRI volumes, including the normalised MEP values at vertices corresponding to the TMS grid locations. These maps were registered to a common atlas, and statistical parametric mapping was used to identify cortical clusters in which stimulation differentially modulated conditioned MEPs across conditions. We found five significant clusters in the frontal cortex. Three clusters in ventral premotor regions (areas 6v and 44) showed significant differential modulations of contralateral MEPs when rest was compared to Prep-ABD and Prep-PG. Two clusters in rostral dorsolateral prefrontal cortex (areas 8Av and 46) showed differential modulation in MEPs when Prep-ABD was compared to Prep-PG. Our findings demonstrate distinct regions that show task-related connectivity whereby interactions between ventral premotor regions and cM1 differentiate between rest and movement preparation and the dorsolateral prefrontal cortex differentiates primarily between preparation of different types of hand movements. These results thus demonstrate the utility of dual-coil TMS and MEP motor maps to define fine-grained sub-regions in the human frontal cortex, which are functional and causally involved in hand movements. HighlightsO_LIDual-coil TMS mapping allows defining of fine-grained frontal cortex subdivisions C_LIO_LIFrontal cortex houses multiple areas with different neurophysiological properties C_LIO_LIInteractions between premotor areas and M1 control rest vs movement C_LIO_LIInteractions between prefrontal areas and M1 reflect movement selection C_LI

neuroscience↗

bioRxiv2019

The observation of explicit and implicit visuomotor cues can drive predictive motor control

Recent studies have highlighted that the observation of hand-object interactions can influence perceptual weight judgements made by an observer. Moreover, observing explicit motor errors during object lifting allows individuals to update their internal sensorimotor representation about object weight. Embodying observed visuomotor cues for the planning of a motor command further enables individuals to accurately scale their fingertip forces when subsequently lifting the same object. However, it is still unknown whether observation of a skilled lift is equally able to mediate predictive motor control in the observer. Here, we tested this hypothesis by asking participants to grasp and lift a manipulandum after observing an actors lift. The object weight changed unpredictably (light or heavy) every third to sixth trial performed by the actor. Participants were informed that they would always lift the same weight as the actor and that, based on the experimental condition, they would have to observe skilled or erroneously performed lifts. Our results revealed that the observation of both skilled and erroneously performed lifts allows participants to update their internal sensorimotor object representation, in turn enabling them to predict force scaling accurately. These findings suggest that the observation of explicit as well as implicit visuomotor cues are embodied in the observers motor repertoire and can drive changes in predictive motor control.

neuroscience↗

bioRxiv2019

Dynamic size-weight changes after object lifting reduce the size-weight illusion

In the size-weight illusion, the smaller object from two equally weighted objects is typically perceived as being heavier. One explanation is that the mismatch between the weight expectation based on object size and actual sensory feedback influences heaviness perception. In most studies, the size of an object is perceived before its weight. We investigated whether size changes would influence weight perception if both would be perceived simultaneously. We used virtual reality to change the size and weight of an object after lifting and asked participants to judge whether objects became lighter or heavier. We found that simultaneous size-weight changes greatly reduced the size-weight illusion to perceptual biases below discrimination thresholds. In a control experiment in which we used a standard size-weight illusion protocol with sequential lifts of small and large objects in the same virtual reality setup, we found a larger, typical perceptual bias. These results show that the size-weight illusion is smaller when size and weight information is perceived simultaneously. This provides support for the prediction mismatch theory explaining the size-weight illusion. Furthermore, these findings suggest that the lifting phase is a critical time window during which brain mechanisms comparing perceived and expected weight mediate the size-weight illusion.

neuroscience↗

bioRxiv2018

Visual delay affects force scaling and weight perception when lifting objects in virtual reality

Lifting an object requires precise scaling of fingertip forces based on a prediction of object weight. At object contact, a series of tactile and visual events arise that need to be rapidly processed online to fine-tune the planned motor commands for lifting the object. The brain mechanisms underlying multisensory integration serially at transient sensorimotor events, a general feature of actions requiring hand-object interactions, are not yet understood. Here we tested the relative weighting between haptic and visual signals when they are integrated online into the motor command. We used a new virtual reality setup to desynchronize visual feedback from haptics, which allowed us to probe the relative contribution of haptics and vision in driving participants movements when they grasped virtual objects simulated by two force-feedback robots. We found that visual delay changed the profile of fingertip force generation and led participants to perceive objects as heavier than when lifts were performed without visual delay. We further modeled the effect of vision on motor output by manipulating the extent to which delayed visual events could bias the force profile, which allowed us to determine the specific weighting the brain assigns to haptics and vision. Our results show for the first time how visuo-haptic integration is processed at discrete sensorimotor events for controlling object lifting dynamics and further highlight the organization of multisensory signals online for controlling action and perception.\n\nNew & NoteworthyDexterous hand movements require rapid integration of information from different senses, in particular touch and vision, at different key time points as movement unfolds. The relative weighting of vision and haptics for object manipulation is unknown. We used object lifting in virtual reality to desynchronize visual and haptic feedback and find out their relative weightings. Our findings shed light on how rapid multisensory integration is processed over a series of discrete sensorimotor control points.

neuroscience↗

bioRxiv2018

Sensorimotor memory for object weight is based on previous experience during lifting, not holding

To allow skilled object manipulation, the brain must generate a motor command specifically tailored to the object properties. For instance, in object lifting, the forces applied by the fingertips must be scaled to the objects weight. When lifting a series of objects, forces are usually scaled according to recent experience from previously lifted objects, an effect often referred to as sensorimotor memory. In this study, we investigated the specific time period during which stored information from previous object manipulation is used to mediate sensorimotor memory. More specifically, we examined whether sensorimotor memory was based on weight information obtained between object contact and lift completion (lifting phase) or during stable holding (holding phase). Participants lifted objects in virtual reality that could increase or decrease in weight after the object was lifted and held in the air. In this way, we could distinguish whether the force planning in the next lift was scaled depending on weight information gathered from either the dynamic lifting or static holding period. We found that force planning was based on the previous object weight experienced during the lifting, but not holding, phase. This suggest that the lifting phase, while merely lasting a few hundred milliseconds, is a key time period for building up internal object representations used for planning future hand-object interactions.\n\nHIGHLIGHTSO_LIWhen lifting objects, fingertip force scaling is based on the most recent lift\nC_LIO_LIWe investigated what time period is critical for acquiring sensorimotor memory\nC_LIO_LISensorimotor memory is based on weight experienced during previous lift, not hold\nC_LIO_LIThe lifting phase is a key period for building up internal models of object lifting\nC_LI

neuroscience↗

bioRxiv2018

Neural basis of Transcranial Magnetic Stimulation at the single-cell Level

Transcranial Magnetic Stimulation (TMS) can non-invasively modulate neural activity in humans. Despite three decades of research, the spatial extent of the cortical area activated by TMS is still controversial. Moreover, how TMS interacts with task-related activity during motor behavior is unknown. We applied single-pulse TMS over the macaque parietal cortex while recording single-unit activity at various distances from the center of stimulation during grasping. The spatial extent of the TMS-induced activation was remarkably restricted, affecting single neurons in a volume of cortex measuring less than 2 mm. In task-related neurons, TMS evoked a transient excitation followed by reduced activity, which was paralleled by a significantly longer grasping time. Furthermore, TMS- induced activity and task-related activity did not summate in single neurons. These results furnish crucial experimental evidence for the neural basis of the TMS effect at the single-cell level and uncover, the neural underpinnings of behavioral effects of TMS.

neuroscience↗