Biology subjects

Martin, A. K.

Publications and source records attributed to Martin, A. K..

10 recordsLinked to original sources

bioRxiv2026

Vestibular Perturbation Disrupts Source and Reality Monitoring

The vestibular system has been implicated in several aspects of self-representation, including bodily self-location, yet its role in episodic source and reality monitoring remains unclear. Moreover, symptoms of depersonalisation and derealisation (DPDR) have been associated with both vestibular dysfunction and altered source and reality monitoring. We tested whether noisy galvanic vestibular stimulation (nGVS) modulates source and reality monitoring during a word-encoding paradigm and whether this increased symptoms of DPDR. Sixty young adults (N = 30 active nGVS, N = 30 sham) encoded words that varied by context (spoken vs. imagined), agentic source (self vs. other), and valence (positive vs. threat) before completing source/reality judgments. Active nGVS reduced overall accuracy relative to sham on both reality and source monitoring. Across conditions, self-referential items were remembered with greater sensitivity compared to other-referential items, and spoken items were recalled with greater sensitivity than imagined items. We additionally show an interaction effect whereby active nGVS reduced accuracy specifically for imagined and threat-valenced items. Trait DPDR did not moderate the effects of stimulation, although higher trait DPDR was associated with a more liberal reality-monitoring response criterion. Results indicate that transient vestibular perturbation via nGVS can impair source monitoring for internalised and threatening stimuli and impairs cognitive distinctions between internally and externally generated events in general, supporting a role for vestibular input in maintaining self-other and reality boundaries in episodic memory.

neuroscience↗

bioRxiv2026

Hemispheric Dissociation in the Cognitive Control of Word Production

This study investigated the hemispheric contributions of the inferior frontal gyrus (IFG) to word production across constrained and unconstrained tasks. In the present study, we used focal ring transcranial direct current stimulation (tDCS) in a sham-controlled, double-blind design, combined with a Picture-Word Interference (PWI) task and a picture description task. Fifty-four healthy young adults completed both tasks within the same stimulation sessions, receiving anodal stimulation over either the left or right IFG. Following task-specific data exclusions, 52 participants were included in each of the two task analyses. In the PWI task, categorically related distractors produced semantic interference and associatively related distractors facilitated naming in response times, consistent with previous findings. Stimulation did not affect response times. In error rates, the two stimulation sites modulated the associative effect in opposite directions. Anodal stimulation of the left IFG enhanced the associative advantage in error rates, whereas anodal stimulation of the right IFG produced the opposite pattern. In the picture description task, anodal stimulation of the right IFG increased speech rate, producing significant effects on words per minute, unpruned words per minute, and syllables per minute. No equivalent effects emerged in the left IFG group. Lexical diversity and utterance length were unaffected by stimulation. Taken together, these findings provide convergent evidence for a hemispheric dissociation in word production. The right IFG appears to contribute to the regulation of speech output and the control of distractor interference, whereas the left IFG appears to support the retrieval and selection of word meanings.

neuroscience↗

bioRxiv2025

Legal but immoral: attitudes toward non-invasive brain stimulation for cognitive enhancement

Cognitive enhancement involves using substances or technologies to improve mental performance in healthy individuals. While methods such as caffeine are widely accepted, others, including prescription stimulants and non-invasive brain stimulation (tDCS), evoke ethical concern. This study examined how university students evaluate three forms of cognitive enhancement (natural, pharmacological, brain stimulation) across five moral domains: academic fairness, free will, naturalness, self-identity, and safety. We also tested how evaluations were shaped by framing (preservation vs. enhancement) and priming (self-affecting vs. non-self-affecting). A total of 449 students completed an online experiment with a 2 x 2 x 3 mixed design, rating enhancement acceptability after reading intervention-specific scenarios. Natural enhancers were judged most positively, followed by brain stimulation and then pharmacological agents. Importantly, although brain stimulation is legal and marketed as non-invasive, it was evaluated more like pharmacological enhancement than natural methods, indicating that legality does not equate to moral acceptability. Framing effects showed that participants were more accepting of enhancement when it was described as preserving ability rather than augmenting it beyond baseline. Priming participants to consider how others use might affect their own outcomes reduced moral acceptability, particularly for pharmacological and brain stimulation methods in the domain of academic fairness. Overall, public attitudes toward enhancement appeared shaped less by legality or objective safety than by intuitive moral reasoning. These findings highlight the importance of adopting pluralistic, context-sensitive approaches to policy and regulation, as student judgments reflect concerns about fairness, authenticity, and competition in academic life.

neuroscience↗

bioRxiv2025

Stuck on you! Social brain stimulation increases the cognitive effort required to return to the egocentric perspective

Flexible switching between self and other perspectives is critical for adaptive social cognition and is thought to rely on the dynamic regulation of self-other representations. Although neuroimaging implicates the dorsomedial prefrontal cortex (dmPFC) and right temporoparietal junction (rTPJ) in perspective-taking, causal evidence for their specific contributions to perspective switching is lacking. Here, we applied focal transcranial direct current stimulation (f-tDCS) to the dmPFC and rTPJ while participants completed a visual perspective-taking task requiring switches between egocentric and altercentric viewpoints. Anodal stimulation to either site selectively increased the cognitive cost of switching back to the egocentric-perspective, without affecting switches into the altercentric-perspective. Rather than facilitating re-engagement with self-referential processing, stimulation enhanced altercentric persistence or impaired disengagement from the altercentric perspective. These findings provide novel causal evidence that both the dmPFC and rTPJ are involved in regulating the inhibition and updating of self-other representations during perspective switching. Results suggest that stimulation of these hubs may disrupt efficient realignment to the self, highlighting their role in maintaining an altercentric cognitive state. Future studies are required to uncover the precise neural computations that account for the comparable behavioural outcomes observed across distinct social brain hubs.

neuroscience↗

bioRxiv2025

Oncolytic HSV-IL27 expression improves CD8 T cell function and therapeutic activity in syngeneic glioma models

BackgroundMalignant gliomas (MG) are the most common primary brain malignancies and are considered universally fatal. Oncolytic HSVs (oHSV) are promising immunotherapeutics capable of selectively lysing cancer cells, eliciting anti-tumor immunity, and providing local delivery of immune-activating transgenes. IL-27 is a pleiotropic cytokine capable of enhancing tumor-reactive cytotoxic T cell (CTL) function while also possessing neuroprotective properties. We hypothesized that IL-27 expression by oHSV would enhance CTL function and improve anti-glioma therapeutic activity. MethodsWe developed an oncolytic herpes simplex virus (oHSV) that expresses IL-27 (C027). The anti-glioma efficacy of C027 was tested in three syngeneic orthotopic glioma models derived from both chemical (CT-2A) and genetic (SB28, KR158) glioma lines. Spectral flow cytometry was used to assess immunophenotypic and functional changes in the tumor infiltrates and systemically. To further investigate the C027-related CTL activity, we employed in vivo cell specific depletion and IL-27 blockade alongside in vitro T cell stimulation assays. Local and systemic antitumor memory was evaluated by both orthotopic and flank tumor rechallenge of C027-treated long-term survivors. ResultsC027 significantly prolonged survival in syngeneic orthotopic glioma models derived from both chemical (CT-2A) and genetic (KR158, SB28) glioma lines. In the CT-2A model, IL-27-expressing oHSV treatment was associated with increased intratumoral multifunctional effector cytotoxic T lymphocytes (CTL) and functional T cell populations systemically. Mechanistically, both CD8 T cells and IL-27 were required for the C027 survival benefit in vivo and IL-27 enhanced CTL function in vitro. C027-treated mice that survived their initial tumors had local and systemic anti-glioma memory rejecting tumors on rechallenge. ConclusionsOur findings demonstrate that IL-27 expression by oHSV significantly improves anti-glioma therapeutic efficacy, enhances CTL effector function, and induces durable immune memory. Thus, IL-27-oHSV may provide a promising therapeutic approach for malignant gliomas. O_LIWhat is already known on this topic - Malignant gliomas are highly aggressive tumors largely resistant to current immunotherapies. Oncolytic herpes simplex viruses (oHSV) are promising immunotherapy agents for malignant gliomas and provide a platform for immunomodulatory gene expression. C_LIO_LIWhat this study adds - In this study, we present a novel IL-27 expressing oHSV (C027) that improves survival in syngeneic glioma-bearing mice through a CD8 T cell and IL-27 dependent mechanism and induces durable immune memory. C_LIO_LIHow this study might affect research, practice or policy - Our study demonstrates that IL-27-expression by oHSV enhances anti-tumor immunity and glioma efficacy suggesting its potential as a novel therapeutic. C_LI

immunology↗

bioRxiv2025

A Causal and Dissociable Role for the Right Inferior Prefrontal Cortex in Empathy for Physical and Social Pain

The right inferior frontal gyrus (rIFG) and dorsomedial prefrontal cortex (dmPFC) are key nodes in the social brain, implicated in empathy for physical and social pain. However, their causal and dissociable contributions remain unclear. In this study, 52 young adults underwent focal transcranial direct current stimulation (f-tDCS) targeting the rIFG or dmPFC in a sham-controlled, double-blind, crossover design. Participants rated the intensity of pain in images depicting social or physical pain during stimulation. Anodal stimulation to the rIFG increased ratings of physical pain and decreased ratings of social pain, suggesting dissociable roles in processing empathy for these two pain types. In contrast, dmPFC stimulation did not modulate ratings, potentially reflecting its role in higher-order social cognitive processes rather than affective empathy. The effects of rIFG stimulation on social pain were significantly stronger in the initial trials, suggesting potential habituation within the rIFG or stimulation-specific effects. These results provide causal, dissociable evidence for the rIFGs involvement in empathy, with its effects differing based on the type of pain. This supports the proposal that distinct neural processes underlie empathy for social versus physical pain.

neuroscience↗

bioRxiv2024

Regionally specific picture naming benefits of focal tDCS are dependent on baseline performance in older adults

AbstractWord-finding difficulty is a common challenge in older age and is linked to various neuropathological conditions associated with ageing. Transcranial direct current stimulation (tDCS) has shown promise as a cognitive enhancement tool for both healthy aging and age- related cognitive disorders. However, its effectiveness in enhancing word-finding ability remains inconsistent, especially among healthy adults. This variability is likely due to factors such as task selection, stimulation parameters, and small sample sizes. Additionally, many studies have overlooked the role of baseline performance in evaluating tDCS efficacy. In this preregistered study, we examined 72 older and 72 younger adults using a double-blind, sham-controlled design, delivering anodal focal tDCS to either the left inferior frontal gyrus or the left temporoparietal junction. Baseline naming performance and fluid intelligence were measured before stimulation. Anodal stimulation of the left inferior frontal gyrus significantly increased response speed for object and action naming in older adults, but crucially only in older adults who performed poorly during the baseline naming session. Findings demonstrate regionally specific effects of focal tDCS in healthy older individuals in greater need for naming facilitation. Notably, performance on a broad measure of fluid intelligence was unrelated to stimulation response, suggesting task specificity of this effect.

neuroscience↗

bioRxiv2019

The right temporoparietal junction is causally associated with embodied perspective taking

Several theories exist pertaining to the role of the right temporoparietal junction (rTPJ) in social cognition. A prominent theory claims the rTPJ is especially associated with embodied processes. In the present study we use high-definition transcranial direct current stimulation (HD-tDCS) to provide evidence that the rTPJ is causally associated with the embodied processes underpinning perspective taking. Eighty-eight young human adults were stratified to receive either rTPJ or dorsomedial prefrontal (dmPFC) anodal HD-tDCS in a sham-controlled, double-blind, repeated-measures design. Perspective tracking (line-of-sight) and perspective taking (embodied rotation) were assessed using a visuo-spatial perspective taking (VPT) task that required understanding what another person could see or how they see it, respectively. Embodied processing was manipulated by positioning the participant in a manner congruent or incongruent with the orientation of an avatar on the screen. As perspective taking, but not perspective tracking, is influenced by bodily posture, this allows the investigation of the specific causal role for the rTPJ in embodied processing. Crucially, anodal stimulation to the rTPJ increased the effect of bodily posture during perspective taking, whereas no such effects were identified during perspective tracking, thereby providing evidence for a causal role for the rTPJ in the embodied component of perspective taking. Stimulation to the dmPFC had no effect on perspective tracking or taking. Therefore, the present study provides support for theories postulating that the rTPJ is causally involved in embodied cognitive processing relevant to social functioning.\n\nSignificance StatementThe ability to understand anothers perspective is a fundamental component of social functioning. Adopting another perspective is thought to involve both embodied and non-embodied processes. The present study used high-definition transcranial direct current stimulation (HD-tDCS) and provided causal evidence that the right temporoparietal junction (rTPJ) is involved specifically in the embodied component of perspective taking. Specifically, HD-tDCS to the rTPJ, but not another hub of the social brain (dmPFC), increased the effect of body posture during perspective taking, but not tracking. This is the first causal evidence that HD-tDCS can modulate social embodied processing in a site-specific and task-specific manner.

neuroscience↗

bioRxiv2018

Cultural background influences electrical stimulation effects on the social brain

ABSTRACTCultural background influences social cognition, however no study has examined brain stimulation differences attributable to cultural background. 104 young adults [52 South-East Asian Singaporeans (SEA); 52 Caucasian Australians (CA)] received anodal high-definition transcranial direct current stimulation (HD-tDCS) to the dorsomedial prefrontal cortex (dmPFC) or the right temporoparietal junction (rTPJ). Participants completed tasks with varying demands on self-other processing including visual perspective taking and episodic memory with self and other encoding. At baseline, SEA showed greater self-other integration than CA in the level one (line-of-sight) VPT task as indexed by greater interference from the alternate perspective. Anodal HD-tDCS to the dmPFC resulted in the CA performing closer to the SEA during egocentric perspective judgements. Baseline performance on level two (embodied rotation) VPT task and the self-reference effect in memory (SRE) was comparable between the two groups. In the combined sample, HD-tDCS to the rTPJ decreased the interference from the egocentric perspective during level two VPT and dmPFC HD-tDCS removed the SRE in episodic memory. Stimulation effects were comparable when baseline performance was comparable. When baseline performance differed, stimulation differences were identified. Therefore, social cognitive differences due to cultural background are an important consideration in social brain stimulation studies.\n\nHIGHLIGHTSO_LICompared with Caucasians, South-East Asians were influenced by the alternate perspective to a greater extent during level one visual perspective taking\nC_LIO_LIAnodal HD-tDCS to the dmPFC shifted Caucasians closer to the baseline performance of South-East Asians\nC_LIO_LIAnodal HD-tDCS to the dmPFC removed the self-reference effect in episodic memory in both cultural groups\nC_LIO_LIAnodal HD-tDCS to the dmPFC reduced overall memory performance in the South-East Asians but not in the Caucasian group\nC_LIO_LIAnodal HD-tDCS to the rTPJ reduced egocentric interference in a level two visual perspective taking task in both cultural groups\nC_LI

neuroscience↗

bioRxiv2018

Dissociable roles for the rTPJ and dmPFC in self-other processing: a HD-tDCS study

BackgroundSocial interaction relies on the integration and distinction of self and other. The dorsomedial prefrontal cortex (dmPFC) and the right temporoparietal junction (rTPJ) are two regions consistently associated with social processes. Theories of rTPJ function in social cognition include self-other distinction, self-inhibition, or embodied mental rotation, whereas the dmPFC is associated with a wide range of social functions involving understanding and encoding information pertaining to others. However, to date, no study has provided causal evidence for dissociable roles of the rTPJ and dmPFC in social cognition.\n\nMethod52 healthy young adults were stratified into two studies and received either dmPFC or rTPJ anodal HD-tDCS in a sham-controlled, double-blinded, repeated measures design. Subjects completed a social cognitive battery measuring self-other processing across an implicit and explicit level one (line-of-sight) and level two (mental rotation) visual perspective taking tasks (VPT), as well as self and other encoding effects on episodic memory in order to test the self-reference effect (SRE).\n\nResultsStimulation of the dmPFC selectively enhanced integration of the other perspective into self as indexed by an increase in congruency effect (incongruent-congruent) across both explicit VPT tasks. It also removed the SRE in episodic memory, indexed by increasing the recognition of other-encoded words and reducing the recognition of self-encoded words. Stimulation of the rTPJ resulted in improved inhibition of the self-perspective during level two VPT only, as indexed by a reduction of the congruency effect when taking the other perspective.\n\nConclusionOur results provide the first causal evidence for dissociable roles of the dmPFC and rTPJ in social cognition. This research supports theories suggesting that rTPJ facilitates embodied mental rotation, whereas the dmPFC integrates information relevant to the other into that of the self.

neuroscience↗