Global organization of neuronal activity only requires unstructured local connectivity

Modern electrophysiological recordings simultaneously capture single-unit spiking activities of hundreds of neurons spread across large cortical distances. Yet, this parallel activity is often confined to relatively low-dimensional manifolds. This implies strong coordination also among neurons that are most likely not even connected. Here, we combine in vivo recordings with network models and theory to characterize the nature of mesoscopic coordination patterns in macaque motor cortex and to expose their origin: We find that heterogeneity in local connectivity supports network states with complex long-range cooperation between neurons that arises from multi-synaptic, short-range connections. Our theory explains the experimentally observed spatial organization of covariances in resting state recordings as well as the behaviorally related modulation of covariance patterns during a reach-to-grasp task. The ubiquity of heterogeneity in local cortical circuits suggests that the brain uses the described mechanism to flexibly adapt neuronal coordination to momentary demands.

Is there a lower visual field preference in object affordances? A registered report.

It’s been repeatedly shown that pictures of graspable objects can facilitate visual processing and motor responses, even in the absence of reach-to-grasp actions, an effect often attributed the concept of affordances, originally introduced by Gibson (1979). A classic demonstration of this is the handle compatibility effect, which is characterised by faster reaction times when the orientation of a graspable object’s handle is compatible with the hand used to respond, even when the handle orientation is task irrelevant. Nevertheless, whether faster RTs are due to affordances or spatial compatibility effects has been significantly debated. In the proposed studies, we will use a stimulus-response compatibility paradigm to investigate firstly, whether we can replicate the handle compatibility effect while controlling for spatial compatibility. Here, participants will respond with left- or right-handed keypresses to whether the object is upright or inverted and, in separate blocks, whether the object is red or green. RTs will be analysed using repeated-measures ANOVAs. In line with an affordance account, we hypothesise that there will be larger handle compatibility effects for upright/inverted compared to colour judgements, as colour judgements do not require object identification and are not thought to elicit affordances. Secondly, we will investigate whether the handle compatibility effect shows a lower visual field (VF) advantage in line with functional lower VF advantages observed for hand actions. We expect larger handle compatibility effects for objects viewed in the lower VF than upper VF, given that the lower VF is the space where actions most frequently occur.

High-gamma mirror activity patterns in the human brain during reach-to-grasp movement observation, retention, and execution—An MEG study

While the existence of a human mirror neuron system is evident, the involved brain areas and their exact functional roles remain under scientific debate. A number of functionally different mirror neuron types, neurons that selectively respond to specific grasp phases and types for example, have been reported with single cell recordings in monkeys. In humans, spatially limited, intracranially recorded electrophysiological signals in the high-gamma (HG) range have been used to investigate the human mirror system, as they are associated with spiking activity in single neurons. Our goal here is to complement previous intracranial HG studies by using magnetoencephalography to record HG activity simultaneously from the whole head. Participants performed a natural reach-to-grasp movement observation and delayed imitation task with different everyday objects and grasp types. This allowed us to characterize the spatial organization of cortical areas that show HG-activation modulation during movement observation (mirroring), retention (mnemonic mirroring), and execution (motor control). Our results show mirroring related HG modulation patterns over bilateral occipito-parietal as well as sensorimotor areas. In addition, we found mnemonic mirroring related HG modulation over contra-lateral fronto-temporal areas. These results provide a foundation for further human mirror system research as well as possible target areas for brain-computer interface and neurorehabilitation approaches.

The Emergence of Stereotyped Kinematic Synergies when Mice Reach to Grasp Following Stroke

Reaching tasks are commonly used in preclinical and clinical studies to assess the acquisition of fine motor skills and recovery of function following stroke. These tasks are often used to assess functional deficits in the absence of quantifying the quality of movement which requires kinematic analysis. To meet this need, this study uses a kinematic analysis in mice performing the Montoya staircase task at 5 and 14 days following a cortical photothrombosis-induced stroke. Following stroke, the mice had reaching impairments associated with sustained deficits including longer, unsmooth, and less individuated paw trajectories. Two weeks after stroke we also detected the emergence of abnormal elbow and shoulder angles, flexion/extensions, and stereotyped kinematic synergies. These data suggest that proximal and distal segments acting in concert is paramount during post-stroke reaching and encourage further analysis of synergies within the translational pipeline of preclinical to clinical studies.

Modulation of cutaneous responses in the cuneate nucleus of macaques during active movement

To achieve stable and precise movement execution, the sensorimotor system integrates exafferent sensory signals originating from interactions with the external world and reafferent signals caused by our own movements. This barrage of sensory information is regulated such that behaviorally relevant signals are boosted at the expense of irrelevant ones. For example, sensitivity to touch is reduced during movement - when cutaneous signals caused by skin stretch are expected and uninteresting - a phenomenon reflected in a decreased cutaneous responsiveness in thalamus and cortex. Some evidence suggests that movement gating of touch may originate from the cuneate nucleus (CN), the first recipient of signals from tactile nerve fibers along the dorsal columns medial lemniscal pathway. To test this possibility, we intermittently delivered mechanical pulses to the receptive fields (RFs) of identified cutaneous CN neurons as monkeys performed a reach-to-grasp task. As predicted, we found that the cutaneous responses of individual CN neurons were reduced during movement. However, this movement gating of cutaneous signals was observed for CN neurons with RFs on the arm but not those with RFs on the hand. We conclude that sensory gating occurs in the first processing stage along the somatosensory neuraxis and sculpts incoming signals according to their task relevance.

Observation of others’ actions during limb immobilization prevents the subsequent decay of motor performance

There is rich clinical evidence that observing normally executed actions promotes the recovery of the corresponding action execution in patients with motor deficits. In this study, we assessed the ability of action observation to prevent the decay of healthy individuals’ motor abilities following upper-limb immobilization. To this end, upper-limb kinematics was recorded in healthy participants while they performed three reach-to-grasp movements before immobilization and the same movements after 16 h of immobilization. The participants were subdivided into two groups; the experimental group observed, during the immobilization, the same reach-to-grasp movements they had performed before immobilization, whereas the control group observed natural scenarios. After bandage removal, motor impairment in performing reach-to-grasp movements was milder in the experimental group. These findings support the hypothesis that action observation, via the mirror mechanism, plays a protective role against the decline of motor performance induced by limb nonuse. From this perspective, action observation therapy is a promising tool for anticipating rehabilitation onset in clinical conditions involving limb nonuse, thus reducing the burden of further rehabilitation.

Root-To-Shoot Signaling for the Coding of Support Thickness in Pea Plants

Plants characterized by a soft or weak steam, such as climbing plants, need to find a potential support (e.g., wooden trunk) to reach greater light exposure. Since Darwin’s research on climbing plants, several studies on their searching and attachment behaviors have demonstrated their unique ability to process different support features to modulate their movements accordingly. Nevertheless, the strategies underlying this ability are yet to be uncovered. The present research tries to fill this gap by investigating how the interaction between above- (i.e., stem, tendril, …) and belowground (i.e., the root system) plant organs influence the kinematics of the approach-to-grasp movement. With three-dimensional (3D) kinematical analysis, we characterized the movement of pea plants (Pisum sativum L.) towards a support with different thicknesses above and belowground (i.e., thin below, thick aboveground, or the opposite). As a control condition, the plants were presented to supports with the same thickness below- and aboveground (i.e., either entirely thin or thick). The results suggest an integration between the information from below- and aboveground for driving the reach-to-grasp behavior of the aerial plant organs. Information about the support conveyed by the root system seems particularly important to fulfil the end-goal of the movement.

Movement as a window to the mind: grasping adults’ perception and understanding of others’ goal-directed movements

<p>Did you know you are a mindreader? Most of us have a fundamental curiosity about people and are in fact engaging in the process of mindreading every day, as we navigate our social worlds. For instance, we often think about what other people are thinking. On a more basic level, we even predict others’ goals based on their actions, such as when they reach for and grasp objects in their environment. This thesis aimed to test and validate a classic action observation paradigm. In order to do so, three experiments were conducted to investigate action observation for goal-directed movements. In Experiment 1, adults' eye gaze was tracked as they viewed reach-to-grasp movements. Contrary to standard predictions, results did not replicate gaze proactivity according to a motor matching account. Rather, adults' eyes latched on to targets that were larger and/or nearer to the agent’s hand. A motor matching account would have predicted that grasp type (pincer grasp or whole-hand prehension) should cue gaze proactivity to the congruent target (i.e., small object or large object, respectively). In Experiment 2, adults’ reaction times were measured as they viewed the same stimuli, but presented in static rather than dynamic format. Similarly to Experiment 1, adults’ response times were faster to detect a target when it appeared over an object closer to the reaching hand, rather than an object farther away from the hand. Again, this was not in line with a motor matching account. Finally, in Experiment 3, adults’ explicit probability judgements were solicited for still frames taken from the original video stimuli. Yet again, a distance effect prevailed, whereby adults explicitly predicted that the agent’s hand would contact the closer of two objects, even when the hand was at rest (in the absence of any motor cue). Overall, these results imply that adults are applying non-motor heuristics during action observation. As such, the stimuli tested in these classical studies may not be fit for purpose, that is, they do not reliably show a motor matching effect during action observation in adults. The implications of these findings for future research and theorising are also discussed.</p>