Biology subjects

Carter, M. J.

Publications and source records attributed to Carter, M. J..

7 recordsLinked to original sources

bioRxiv2025

Deliberation is a controllable process governed by desirability and cognitive effort

Humans spend a lifetime making decisions based on incoming sensory information and goals. Prominent theories of perceptual decision-making have described the components of deliber-ation process, yet they lack a unifying principle that governs how the nervous system tunes the deliberation process across multiple contexts. Desirability (reward) and effort (energy) are major determinants in governing a broad range of human and animal behaviour, such as for-aging, walking, and decisions. Here we develop a theory where desirability and cognitive effort tune the control gains that govern deliberation. Several hallmark features of decision behaviour simply emerge from the model, with the deliberation process closely resembling low-dimensional neural dynamics. We also predict and provide a novel mechanistic explanation for choking-under-pressure, where extremely large rewards lead to performance deficits. Our principled framework explains both behavioural and neural phenomena while providing a path to unify disparate fields.

neuroscience↗

bioRxiv2025

Cerebrovascular Responses to Static and Rhythmic Handgrip Exercises

Handgrip exercise (HGE) is a safe, accessible exercise modality shown to improve cardiovascular health and is particularly promising for individuals with limited mobility who cannot engage in traditional exercise. Given that contraction type and intensity influence systemic cardiorespiratory variables that affect cerebral blood flow regulation, this study examined the acute systemic hemodynamic and cerebrovascular responses to static and rhythmic HGE protocols at varying intensities. Thirty-three healthy young adults (17 males; 16 females age 22(1) years) performed four separate 5-minute HGE protocols in a randomized order: static HGE at 15% (S15) of maximal voluntary contraction (MVC), static HGE at 30% MVC, rhythmic HGE at 30% MVC, rhythmic HGE at 60% (R60) MVC. We hypothesized that rhythmic HGE at higher intensities would produce the greatest cerebrovascular responses due to enhanced venous return and cardiac output, while static HGE at higher intensities would elicit the greatest systemic (i.e., blood pressure, HR, ventilation) responses. Cerebral (middle cerebral artery blood velocity [MCAv] and cerebrovascular conductance index [MCACVCi], internal carotid artery [ICA] diameter, velocity, blood flow, and shear rate) and systemic hemodynamics (systolic [SBP], diastolic [DBP], mean arterial pressure [MAP], heart rate [HR], cardiac output [CO]), and end-tidal carbon dioxide (PETCO2) levels were averaged over the final 30s of each minute of exercise. There was a significant time and protocol interaction effect on HR (p<0.001). We found significant main effects of exercise protocol for MCAv (p<0.001), MCACVCi (p<0.001), ICA diameter (p=0.01) and blood flow (p=0.001), and PETCO2 (p=0.002). Greatest increases in MCAv alongside the largest reduction in ICA blood flow occurred in R60. The greatest increase in MCACVCi and ICA blood flow (from baseline) occurred in R30 compared to other protocols. In addition to the greater cerebrovascular responses, we also observed more modest systemic responses (lower HR, MAP, CO) and lower self-reported ratings of perceived exertion (p<0.001) in R30 compared to other protocols. Acute increases in MCACVCi and ICA blood flow observed in R30 (despite the lower perceived effort) may suggest that rhythmic HGE at low-moderate intensities can be a tolerable prescription for inducing exercise-related cerebrovascular adaptations (i.e., improved cerebral perfusion) in populations that may require adapted physical activity.

physiology↗

bioRxiv2025

Involuntary feedback responses reflect a representation of partner actions

We have a remarkable ability to seamlessly and rapidly coordinate actions with others, from double dutch to dancing. Humans use high-level partner representations to jointly control voluntary actions, while other work shows lower-level involuntary feedback responses to sudden visual perturbations. Yet, it is unknown if a high-level partner representation can be rapidly expressed through lower-level involuntary sensorimotor circuitry. Here we test the idea that a partner representation influences involuntary visuomotor feedback responses during a cooperative sensorimotor task. Using two experiments and dynamic game theory predictions, we show that involuntary visuomotor feedback responses reflect a partner representation and consideration of a partners movement cost (i.e., accuracy and energy). Collectively, our results suggest there is top-down modulation from high-level partner representations to lower-level sensorimotor circuits, enabling fast and flexible feedback responses during jointly coordinated actions. Significance StatementHumans have an adept ability to rapidly coordinate their movements with others. Yet it is unknown how fast the sensorimotor system can use a representation of others to jointly control movement. Remarkably, intelligent reflexes (i.e., involuntary visuomotor feedback responses) consider high-level partner representations within 180 - 230 ms. Further, these involuntary visuomotor feedback responses show that the sensorimotor system is willing sacrifice energy to help a partner.

neuroscience↗

bioRxiv2024

Online movements reflect ongoing deliberation

From navigating a crowded hallway to skiing down a treacherous hill, humans are constantly making decisions while moving. Insightful past work has provided a glimpse of decision deliberation at the moment of movement onset. Yet it is unknown whether ongoing deliberation can be expressed during movement, following movement onset and prior to any decision. Here we tested the idea that an ongoing deliberation continually influences motor processes--prior to a decision--directing online movements. Over three experiments, we manipulated evidence to influence deliberation during movement. The deliberation process was manipulated by having participants observe evidence in the form of tokens that moved into a left or right target. Supporting our hypothesis we found that lateral hand movements reflected deliberation, prior to a decision. We also found that a deliberation urgency signal, which more heavily weighs later evidence, was fundamental to predicting decisions and explains past movement behaviour in a new light. Our paradigm promotes the expression of ongoing deliberation through movement, providing a powerful new window into understanding the interplay between decision and action.

neuroscience↗

bioRxiv2023

Reinforcement-Based Processes Actively Regulate MotorExploration Along Redundant Solution Manifolds

From a babys babbling to a songbird practicing a new tune, exploration is critical to motor learning. A hallmark of exploration is the emergence of random walk behaviour along solution manifolds, where successive motor actions are not independent but rather become serially dependent. Such exploratory random walk behaviour is ubiquitous across species, neural firing, gait patterns, and reaching behaviour. Past work has suggested that exploratory random walk behaviour arises from an accumulation of movement variability and a lack of error-based corrections. Here we test a fundamentally different idea--that reinforcement-based processes regulate random walk behaviour to promote continual motor exploration to maximize success. Across three human reaching experiments we manipulated the size of both the visually displayed target and an unseen reward zone, as well as the probability of reinforcement feedback. Our empirical and modelling results parsimoniously support the notion that exploratory random walk behaviour emerges by utilizing knowledge of movement variability to update intended reach aim towards recently reinforced motor actions. This mechanism leads to active and continuous exploration of the solution manifold, currently thought by prominent theories to arise passively. The ability to continually explore muscle, joint, and task redundant solution manifolds is beneficial while acting in uncertain environments, during motor development, or when recovering from a neurological disorder to discover and learn new motor actions.

neuroscience↗

bioRxiv2020

Gaze Behaviour Reveals Flexible Encoding of Competing Reach Goals Under Conditions of Target Uncertainty

In daily tasks, we are often confronted with competing potential targets and must select one to act on. It has been suggested that, prior to target selection, the human brain encodes the motor goals of multiple, potential targets. However, this view remains controversial and it has been argued that only a single motor goal is encoded, or that motor goals are only specified after target selection. To investigate this issue, we measured participants gaze behaviour while viewing two potential reach targets, one of which was cued after a preview period. We applied visuomotor rotations to dissociate each visual target location from its corresponding motor goal location; i.e., the location participants needed to aim their hand toward to bring the rotated cursor to the target. During the preview period, participants most often fixated both motor goals but also frequently fixated one, or neither, motor goal location. Further gaze analysis revealed that on trials in which both motor goals were fixated, both locations were held in memory simultaneously. These findings show that, at the level of single trials, the brain most often encodes multiple motor goals prior to target selection, but may also encode either one or no motor goals. This result may help reconcile a key debate concerning the specification of motor goals in cases of target uncertainty.

neuroscience↗

bioRxiv2019

Geographical origin determines responses to salinity of Mediterranean caddisflies

Many freshwater ecosystems worldwide, and particularly Mediterranean ones, show increasing levels of salinity. This changes in water conditions could affect abundance and distribution of inhabiting species as well as the provision of ecosystem services. In this study we conduct laboratory experiments using the macroinvertebrate Smicridea annulicornis as a model organism. Our factorial experiments were designed to evaluate the effects of geographical origin on organisms and salinity levels on survival and behavioral responses of caddisflies. The experimental organisms were captured from rivers belonging to three hydrological basins along a 450 Km latitudinal gradient in the Mediterranean region of Chile. Animals were exposed to three conductivity levels, from 180 to 1400 S/cm, close to the historical averages of the source rivers. We measured the behavioral responses to experimental stimulii and the survival time. Our results showed that geography origin shaped the behavioral and survival responses to salinity. In particular, survival and activity decreased more strongly with increasing salinity in organisms coming from more dilute waters. This suggests local adaptation to be determinant for salinity responses in this species of benthic invertebrate. In the current scenario of fast temporal and spatial changes in water levels and salt concentration, the conservation of geographic intra-specific variation of aquatic species is crucial for lowering the risk of salinity-driven biodiversity loss.

ecology↗