Biology subjects

Filmer, H.

Publications and source records attributed to Filmer, H..

3 recordsLinked to original sources

bioRxiv2024

On the neural substrates of mind wandering and dynamic thought: A drug and brain stimulation study

The impact of mind wandering on our daily lives ranges from diminishing productivity, to facilitating creativity and problem solving. There is evidence that distinct internal thought types can be modulated by transcranial direct current stimulation (tDCS), although little is known about optimal stimulation parameters or the mechanisms behind such effects. In addition, recent findings suggest changes in dopamine availability may alter the effect tDCS has on neural and behavioural outcomes. Dopaminergic functioning has also been implicated in executive processes anticorrelated with mind wandering such as attention and working memory, however the neurochemical mechanisms involved in internal thoughts are largely unknown. Here, we investigated the role of dopamine, and tDCS, on internal thought processes. Specifically, using an attentional control task, we tested whether dopamine availability (levodopa or placebo) mediated the effects of online high definition tDCS (HD-tDCS; 2mA, or sham). There was no evidence for our hypothesised effect of left prefrontal cortex HD-tDCS reducing task unrelated thought, nor freely moving thought. This failure to replicate previous HD-tDCS findings emphasises the importance of employing robust methodological practices within this field to improve confidence in the findings. However, we did find that levodopa reduced freely moving thought, relative to placebo. We also found preliminary evidence that dopamine availability may moderate the relationship between stimulation and behavioural variability performance during periods of task unrelated thought. Overall, these findings suggest that stimulation does not affect dynamic internal thought, however there is initial evidence for the potential effectiveness of targeting the dopaminergic system to reduce spontaneous internal thoughts and improve behavioural performance.

neuroscience↗

bioRxiv2023

On the role of prefrontal and parietal cortices in mind wandering and dynamic thought

Mind wandering is a common phenomenon in our daily lives and can have both an adaptive and detrimental impact. Recently, a dynamic framework has been proposed to characterise the heterogeneity of internal thoughts, suggesting there are three distinct thought types which can change over time - freely moving, deliberately constrained, and automatically constrained (thoughts). There is very little evidence on how different types of dynamic thought map onto the brain. Previous research has applied non-invasive transcranial direct current stimulation (tDCS) to causally implicate the prefrontal cortex and inferior parietal lobule in general mind wandering. However, a more recently developed and nuanced technique, high-definition tDCS (HD-tDCS), delivers more focal stimulation able to target specific brain regions. Therefore, the current study investigated the effect of anodal HD-tDCS applied to the left prefrontal and right inferior parietal cortices (with the occipital cortex included as an active control) on mind wandering, and specifically, the causal neural substrates of the three internal dynamic thought types. This was a single session study using a novel task which allows investigation into how dynamic thoughts are associated with behavioural variability and the recruitment of executive control operations across the three brain regions. Anodal stimulation to the prefrontal cortex decreased freely moving thought and anodal stimulation to the parietal lobule decreased deliberately constrained thought, with preliminary evidence for an increase in freely moving thought in the occipital cortex as well. These findings support the heterogenous nature of mind wandering, revealing that different brain regions are implicated in distinct dynamic thought types.

neuroscience↗

bioRxiv2023

Intensity-dependent effects of tDCS on motor learning are related to dopamine

Non-invasive brain stimulation techniques, such as transcranial direct current stimulation (tDCS), are popular methods for inducing neuroplastic changes to alter cognition and behaviour. One challenge for the field is to optimise stimulation protocols to maximise benefits. For this to happen, we need a better understanding of how stimulation modulates cortical functioning/behaviour. To date, there is increasing evidence for a dose-response relationship between tDCS and brain excitability, however how this relates to behaviour is not well understood. Even less is known about the neurochemical mechanisms which may drive the dose-response relationship between stimulation intensities and behaviour. Here, we examine the effect of three different tDCS stimulation intensities (1mA, 2mA, 4mA anodal motor cortex tDCS) administered during the explicit learning of motor sequences. Further, to assess the role of dopamine in the dose-response relationship between tDCS intensities and behaviour, we examined how pharmacologically increasing dopamine availability, via 100mg of levodopa, modulated the effect of stimulation on learning. In the absence of levodopa, we found that 4mA tDCS improved and 1mA tDCS impaired acquisition of motor sequences relative to sham stimulation. Conversely, levodopa reversed the beneficial effect of 4mA tDCS. This effect of levodopa was no longer evident at the 48-hour follow-up, consistent with previous work characterising the persistence of neuroplastic changes in the motor cortex resulting from combining levodopa with tDCS. These results provide the first direct evidence for a role of dopamine in the intensity-dependent effects of tDCS on behaviour.

neuroscience↗