Biology subjects

Takamura, Y.

Publications and source records attributed to Takamura, Y..

4 recordsLinked to original sources

bioRxiv2026

Classical music in cognitive rehabilitation: Three case studies of spatial neglect

Chronic spatial neglect after right-hemisphere stroke reflects network dysfunction, with recovery influenced by structural connectivity. Music recruits coordinated bi-hemispheric activity and may promote interhemispheric communication after stroke. Following our pilot study in post-stroke aphasia, we asked whether classical music modulates connectivity and behavior in chronic neglect. Three patients completed a crossover protocol comparing two weeks of daily audiovisual classical music with an audiobook control, with neglect, mood, quality-of-life, diffusion MRI, and resting-state high-density EEG measures. All showed right superior longitudinal fasciculus II disconnection with preserved callosal pathways. In N2, line bisection shifted leftward across all five lines after music, together with increased posterior interhemispheric theta-band weighted symbolic mutual information (wSMI), then deteriorated into the pathological range after the audiobook, without mood improvement. N1 showed mixed behavioral effects, with mood and quality of life improving after music. N3 showed no significant spatial improvement and worsened mood after music. These heterogeneous responses motivate larger studies of connectional predictors. The findings support the feasibility of classical music as an adjunct to neglect rehabilitation and suggest that cognitive changes may occur independently of mood, while the audiobook cannot be considered an inert control.

neuroscience↗

bioRxiv2026

Fronto-temporal structural alterations in congenital aphantasia

Congenital aphantasia is characterized by a lifelong self-reported absence of voluntary visual imagery despite preserved visual knowledge, offering a natural model for dissociating sensory representation from conscious imagery. Functional imaging evidence suggests that this dissociation may arise from altered top-down interactions between higher-order control systems and high-level visual cortex, but its structural correlates remain unknown. Here, using diffusion and structural MRI in 18 individuals with congenital aphantasia and 18 matched visualisers, we tested two competing accounts of aphantasia: one predicting structural differences in visual pathways, the other predicting differences in higher-order associative networks. Across multimodal analyses of white-matter tract microstructure, functional-ROI tractography, graph-theoretic network organization, and cortical morphometry, aphantasia was associated with structural differences in frontotemporal and cingulate white-matter tracts, including the uncinate fasciculus, posterior interparietal callosal fibres, and dorsal cingulum, and in frontotemporal cortical regions, including the anterior insula, anterior prefrontal cortex, and medial temporal cortex, together forming a candidate neuroanatomical signature for the broad cognitive-affective profile of aphantasia. By contrast, we found no reliable group differences in early visual cortex, major visual tracts, or the direct structural connections of the core imagery network. Congenital aphantasia therefore exhibits a pattern of structural alterations centered on frontotemporal and cingulate systems, sparing the principal visual pathways. Given the modest sample size, these findings are exploratory and hypothesis-generating and require replication in larger cohorts; they nonetheless suggest that higher-order systems supporting integration and conscious access, rather than visual representations themselves, may contribute to the absence of conscious imagery in congenital aphantasia.

neuroscience↗

bioRxiv2025

Infraslow histaminergic dynamics govern priming states to gate moment-to-moment memory accessibility

Memory expression fluctuates even in response to identical cues, suggesting that ongoing brain states bias memory accessibility. However, the cellular and circuit principles governing these state-dependent fluctuations remain unclear. Here, we show that spontaneous pre-cue activity of histaminergic neurons in the hypothalamic tuberomammillary nucleus (TMN) modulates the expression of reward-associative memory in mice. TMN histaminergic activity exhibited infraslow dynamics (0.05-0.1 Hz) that closely tracked an integrated brain-body state. Closed-loop cue delivery during high histaminergic states enhanced memory expression. Brief optogenetic activation or inhibition of these neurons before the cue bidirectionally modulated memory expression, and direct activation of histaminergic terminals in the basolateral amygdala (BLA) was sufficient to enhance memory expression. Furthermore, histaminergic inhibition before the cue impaired the cue-evoked BLA population response. Thus, ongoing histaminergic activity exerts an infraslow, state-setting influence that primes BLA circuits for robust cue responses, and in turn, modulates moment-to-moment memory accessibility.

neuroscience↗

bioRxiv2025

Disrupted Integration-Segregation Balance in the Intact Hemisphere in Chronic Spatial Neglect

Spatial neglect is a common and disabling consequence of right hemisphere stroke, characterized by a failure to attend to the contralesional left space, and frequently persists into the chronic stage. There is robust evidence on the role of right-hemisphere frontoparietal dysfunction, interhemispheric structural disconnection and maladaptive activity in the left hemisphere in the persistence of neglect. However, the specific impact of right frontoparietal dysfunction on the functional (re)organization of the left hemisphere remains poorly understood. In this study, we introduce a novel application of functional connectivity gradient analysis to investigate macroscale functional reorganization in the non-lesioned left hemisphere of patients with chronic left spatial neglect. Focusing on resting-state fMRI data, we demonstrate that abnormal segregation patterns in the left frontoparietal and default mode networks are robustly associated with neglect severity and spatial attentional bias. Notably, the principal gradient--typically capturing a global unimodal-to-transmodal hierarchy--was altered in these patients, suggesting a reorganization favoring lateralized unimodal networks. Single-subject analyses confirmed the presence of this pattern in 11 of the 13 patients included in the study. We also show that the structural integrity of the left inferior fronto-occipital fasciculus (IFOF) plays a key role in shaping these functional dynamics. These findings reveal a previously overlooked aspect of neglect pathophysiology: the maladaptive dominance of the non-lesioned hemispheres intrinsic architecture. By combining innovative gradient-based metrics with classical lesion approaches, our study offers a new framework for understanding neglect as an emergent property of large-scale network imbalance, with clinical implications for diagnosis and intervention, and theoretical consequences for models of hemispheric asymmetries and conscious access.

neuroscience↗