Biology subjects

Fraser, D. S.

Publications and source records attributed to Fraser, D. S..

4 recordsLinked to original sources

bioRxiv2023

Dopamine challenge reduces mental state attribution accuracy

Difficulties in reasoning about others mental states (i.e., mentalising / Theory of Mind) are highly prevalent among disorders featuring dopamine dysfunctions (e.g., Parkinsons disease) and significantly affect individuals quality of life. However, due to multiple confounding factors inherent to existing patient studies, currently little is known about whether these socio-cognitive symptoms originate from aberrant dopamine signalling or from psychosocial changes unrelated to dopamine. The present study therefore investigated the role of dopamine in modulating mentalising in a sample of healthy volunteers. We used a double-blind, placebo-controlled procedure to test the effect of the D2 antagonist haloperidol on mental state attribution, using an adaptation of the Heider & Simmel (1944) animations task. On two separate days, once after receiving 2.5mg haloperidol and once after receiving placebo, 33 healthy adult participants viewed and labelled short videos of two triangles depicting mental state (e.g., surprising) and non-mental state (e.g., following) interactions. Using Bayesian mixed effects models we observed that haloperidol decreased accuracy in labelling both mental- and non-mental state animations. Our secondary analyses suggest that dopamine modulates inference from mental- and non-mental state animations via independent mechanisms, pointing towards two putative pathways underlying the dopaminergic modulation of mental state attribution: Action representation and a shared mechanism supporting mentalising and emotion recognition. We conclude that dopamine is causally implicated in Theory of Mind. Our results have implications for the neurochemical basis of socio-cognitive difficulties in patients with dopamine dysfunctions and generate new hypotheses about the specific dopamine-mediated mechanisms underlying social cognition.

neuroscience↗

bioRxiv2023

Dopaminergic manipulations affect the modulation and meta-modulation of movement speed: evidence from two pharmacological interventions

A body of research implicates dopamine in the average speed of simple movements. However, naturalistic movements span a range of different shaped trajectories and rarely proceed at a single constant speed; instead, speed is reduced when drawing "corners" compared to "straights" (i.e., speed-modulation), and the extent of this slowing down is dependent upon the global shape of the movement trajectory (i.e., speed-meta-modulation) - for example whether the shape is an ellipse or a rounded square. By employing two pharmacological intervention studies - individuals with Parkinsons both ON and OFF dopaminergic medication (N = 32) and members of the general population on a D2 receptor blocker (haloperidol) versus placebo (N = 43) - we implicate dopamine in speed, speed-modulation and speed-meta-modulation. Our findings move beyond vigour models implicating dopamine in average movement speed, and towards a conceptualisation that involves the modulation of speed as a function of contextual information.

neuroscience↗

bioRxiv2023

Autistic kinematics diverge from the power laws that typically govern movement

Extant work reliably demonstrates that autistic individuals move with increased jerk (where jerk concerns change in acceleration). Although it follows that autistic movement may therefore diverge from fundamental power laws that govern movement, this hypothesis has not been directly tested to date. This lack of insight holds back progress in understanding the mechanisms underpinning differences in autism in motor control particularly with respect to movement jerkiness. Here we investigated whether movements executed by autistic adults diverged from the typical power law relationship that links movement speed and curvature. x and y position of the stylus tip was recorded at 133 Hz while 21 autistic and 19 non-autistic age-, intelligence quotient- and sex-matched adults traced, on a tablet device, a range of shapes that varied in angular frequency from 2/33 (spiral-like shapes) to 4 (square-like shapes). The gradient of the relationship between speed and curvature for each angular frequency-defined shape is reliably predicted by a set of mathematical equations often referred to as fundamental power laws thus, to assess deviations from power laws, we compared autistic and non-autistic participants in terms of speed-curvature gradients. To gain insight into potential mechanisms underpinning any differences we also used fast Fourier transform to explore amplitude spectral density across all angular frequencies. Compared to non-autistic adults, autistic adults exhibited significantly steeper speed-curvature gradients. Fast Fourier transform further revealed that non-autistic participants exhibited highly precise modulation of speed oscillations around the target frequency. For example, when drawing an ellipse their speed profile was dominated by speed changes in a band centred around the angular frequency 2 with minimal changes in other bands. Autistic adults, in contrast, exhibited less precise modulation of speed oscillations around the target frequency, a result that is reminiscent of a literature reporting broader auditory filters in autistic individuals. These results evidence, in autistic adults, a deviation from the power laws that typically govern movement and suggest differences in motor cortical control policies and/or biomechanical constraints.

neuroscience↗

bioRxiv2022

Dopaminergic modulation of dynamic emotion perception

Emotion recognition abilities are fundamental to our everyday social interaction. A large number of clinical populations show impairments in this domain, with emotion recognition atypicalities being particularly prevalent among disorders exhibiting a dopamine system disruption (e.g., Parkinsons disease). Although this suggests a role for dopamine in emotion recognition, studies employing dopamine manipulation in healthy volunteers have exhibited mixed neural findings and no behavioural modulation. Interestingly, whilst a dependence of dopaminergic drug effects on individual baseline dopamine function has been well established in other cognitive domains, the emotion recognition literature so far has failed to account for these possible interindividual differences. The present within-subjects study therefore tested the effects of the dopamine D2 antagonist haloperidol on emotion recognition from dynamic, whole-body stimuli while accounting for interindividual differences in baseline dopamine. 33 healthy male and female adults rated emotional point-light walkers (PLWs) once after ingestion of 2.5 mg haloperidol and once after placebo. To evaluate potential mechanistic pathways of the dopaminergic modulation of emotion recognition, participants also performed motoric and counting-based indices of temporal processing. Confirming our hypotheses, effects of haloperidol on emotion recognition depended on baseline dopamine function, where individuals with low baseline dopamine showed enhanced, and those with high baseline dopamine decreased emotion recognition. Drug effects on emotion recognition were related to drug effects on movement-based and explicit timing mechanisms, indicating possible mediating effects of temporal processing. Results highlight the need for future studies to account for baseline dopamine and suggest putative mechanisms underlying the dopaminergic modulation of emotion recognition. Significance statementA high prevalence of emotion recognition difficulties amongst clinical conditions where the dopamine system is affected suggests an involvement of dopamine in emotion recognition processes. However, previous psychopharmacological studies seeking to confirm this role in healthy volunteers thus far have failed to establish whether dopamine affects emotion recognition and lack mechanistic insights. The present study uncovered effects of dopamine on emotion recognition in healthy individuals by controlling for interindividual differences in baseline dopamine function and investigated potential mechanistic pathways via which dopamine may modulate emotion recognition. Our findings suggest that dopamine may influence emotion recognition via its effects on temporal processing, providing new directions for future research on typical and atypical emotion recognition.

neuroscience↗