Biology subjects

Filmer, H. L.

Publications and source records attributed to Filmer, H. L..

6 recordsLinked to original sources

bioRxiv2024

Dopamine alters motor learning performance in the presence and absence of feedback

We often choose to learn motor skills not only because of some external reward, but also because motor learning, in and of itself, is satisfying. While dopamine is thought to drive reward-based motor learning, it remains unclear whether dopamine is implicated in motor learning under conditions ostensibly driven by intrinsic rewards/motivation (i.e., in the absence of extrinsic feedback or reward). Here, by pharmacologically manipulating dopamine using the dopamine precursor Levodopa, we investigated the role of dopamine in an explicit motor learning task guided by internally determined signals of performance success, by removing intrinsic feedback about task success. Specifically, we asked participants to strategically aim away from presented targets by various instructed angles: a form of explicit motor learning that contributes to performance in the classic visuomotor rotation task. In the feedback condition, targets jumped mid-movement by the instructed angle, such that success in target hitting depended on successfully aiming away by the instructed angle. In the no-feedback condition, intrinsic feedback about task success was removed by having targets disappear mid-movement, such that participants could not know if they succeeded at hitting the targets or not. We found that dopamine altered performance, both with and without task feedback about task success. This provides direct evidence for a role of dopamine in motor learning driven by internal task goals.

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bioRxiv2023

Stimulating prefrontal cortex facilitates training transfer by increasing representational overlap

Difficulties in multitasking may be the price humans pay for our ability to generalise learning to new tasks. Mitigating these costs through training has been associated with reduced overlap of constituent task representations within a task-related brain network. Transcranial direct current stimulation (tDCS), which can modulate neural activity, has shown promise in generalising training gains. Whether tDCS influences the changes in task-associated representations to produce such training generalisation remains unexplored. Here, we paired prefrontal cortex tDCS with multitasking training, and collected functional magnetic resonance imaging data pre- and post- training. We found that 1mA tDCS enhanced visual search performance, and using machine learning to assess the overlap of brain activity related to the training, show that these generalised gains were predicted by changes in classification accuracy for patterns of frontal, parietal, and cerebellar activity in participants who received left prefrontal cortex stimulation. Thus, prefrontal cortex tDCS interacts with training related changes in task representations, potentially driving the generalisation of learning.

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bioRxiv2023

Dopamine alters the effect of brain stimulation on decision-making

Non-invasive brain stimulation techniques, such as transcranial direct current stimulation (tDCS), show promise in treating cognitive and behavioural impairments in clinical conditions. However, optimisation of such clinical applications requires a better understanding of how tDCS alters cognition and behaviour. Existing evidence implicates dopamine in the way tDCS alters brain activity and plasticity, however, there is as yet no causal evidence for a role of dopamine in tDCS effects on cognition and behaviour. Here, in a preregistered, double-blinded study, we examined how pharmacologically manipulating dopamine altered the effect of tDCS on the speed-accuracy trade-off, which taps ubiquitous strategic cognitive processes. Cathodal tDCS was delivered over the left prefrontal cortex and the superior medial frontal cortex before participants completed a dot-motion task, deciding the direction of moving dots under instructions to emphasize speed, accuracy, or both. We leveraged computational modelling to uncover how our manipulations altered latent decisional processes driving the speed-accuracy tradeoff. We show that dopamine in combination with tDCS (but not tDCS alone, nor dopamine alone) not only impaired decision accuracy, but also impaired discriminability, which suggests that these manipulations altered the encoding or representation of discriminative evidence. This is, to the best of our knowledge, the first direct evidence implicating dopamine in the way tDCS affects cognition and behaviour. Significance statementTranscranial direct current stimulation (tDCS) can improve cognitive and behavioural impairments in clinical conditions, however better understanding of its mechanisms is required to optimise future clinical applications. Here, using a pharmacological approach to manipulate brain dopamine levels in healthy adults, we demonstrate a role for dopamine in the effects of tDCS in the speed-accuracy trade-off, a strategic cognitive process ubiquitous in many contexts. In doing so, we provide direct evidence implicating dopamine in the way tDCS affects cognition and behaviour.

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bioRxiv2023

Dopamine increases accuracy and lengthens deliberation time in explicit motor skill learning.

Although animal research implicates a central role for dopamine in motor skill learning, a direct causal link has yet to be established in neurotypical humans. Here, we tested if a pharmacological manipulation of dopamine alters motor learning, using a paradigm which engaged explicit, goal-directed strategies. Participants (27 females, 11 males, aged 18-29 years) first consumed either 100mg of Levodopa (n=19), a dopamine precursor that increases dopamine availability, or placebo (n=19). Then, during training, participants learnt the explicit strategy of aiming away from presented targets by instructed angles of varying sizes. Targets shifted mid-movement by the instructed aiming angle. Task success was thus contingent upon aiming accuracy. The effect of the dopamine manipulations on skill learning was assessed during training, and at an overnight follow-up. Increasing dopamine availability improved aiming accuracy and lengthened reaction times, particularly for larger, more difficult aiming angles, both at training, and at follow-up. Results support the proposal that dopamine is important in decisions to engage instrumental motivation to optimise performance, particularly when learning to execute goal-directed strategies in motor skill learning.

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bioRxiv2021

Not Quite All in Our Head: Intervention is a Better Predictor of tDCS Mind-Wandering Effects than Subjective Beliefs About Experimental Results

BackgroundEstablishing adequate blinding for non-invasive brain stimulation research is a topic of extensive debate, especially regarding the efficacy of sham control methods for transcranial direct current stimulation (tDCS) studies. Fassi and Cohen Kadosh [1] assessed the influence of subjective participant belief regarding stimulation type (active or sham) and dosage on behaviour using data from Filmer et al. [2] who applied five stimulation protocols (anodal 1.0mA, cathodal 1.0mA, cathodal 1.5mA, cathodal 2.0mA and sham) to assess the neural substrates of mind wandering. Fassi and Cohen Kadosh [1] concluded that subjective belief drove the pattern of results observed by Filmer et al. [2]. ObjectiveFassi and Cohen Kadosh [1] did not assess the key contrast between conditions in Filmer et al. (2019) - 2mA vs sham - rather they examined all stimulation conditions. Here, we consider the relationship between objective and subjective intervention in this key contrast. MethodsWe replicated the analysis and findings of both Filmer et al. [2] and Fassi and Cohen Kadosh [1] before assessing 2mA vs. sham via Bayesian ANOVA on subjective belief regarding stimulation type and dosage. ResultsOur results support objective intervention as the strongest predictor of stimulation effects on mind-wandering when 2mA vs sham was examined, over and above that of subjective intervention. ConclusionsThe conclusions made by Filmer et al. [2] are confirmed. However, it is important to control for and understand the possible effects of subjective beliefs in sham-controlled studies. Best practice to prevent these issues remains the inclusion of active control conditions.

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bioRxiv2020

Age-related differences in the role of the prefrontal cortex in sensory-motor training gains: A tDCS study

The ability to process multiple sources of information concurrently is particularly impaired as individuals age and such age-related increases in multitasking costs have been linked to impairments in response selection. Previous neuroimaging studies with young adults have implicated the left hemisphere prefrontal cortex (PFC) as a key neural substrate of response selection. In addition, several transcranial direct current stimulation studies (tDCS) have provided causal evidence implicating this region in response selection and multitasking operations. For example, Filmer at al. (2013b) demonstrated that typically observed response selection learning/training gains in young adults were disrupted via offline transcranial direct current stimulation (tDCS) of left, but not right, PFC. Here, considering evidence of functional dedifferentiation in the brains of older adults, we assessed if this pattern of response selection learning disruption via tDCS to the left PFC is observed in older adults, testing if this region remains a key response selection node as individuals age. In a pre-registered study with 58 older adults, we applied anodal, cathodal, and sham stimulation to left and right PFC, and measured performance as participants trained on low- and high-response selection load tasks. Active stimulation did not disrupt training in older adults as compared to younger adults. However, there was evidence of enhanced training gains via tDCS, which scaled with response selection task difficulty. The results highlight age-related differences in the casual neural substrates that subserve response selection and learning.

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