Biology subjects

Hamalainen, M. S.

Publications and source records attributed to Hamalainen, M. S..

8 recordsLinked to original sources

bioRxiv2026

Cortical Excitation-Inhibition Balance in Autism Varies by Brain Region and Age

Autism spectrum disorder (ASD) is characterized by differences in social communication, interaction, and restricted and repetitive behaviors. The hypothesis that ASD involves altered cortical excitation-inhibition (EI) balance has been extensively investigated, yet evidence remains mixed, partly because EI balance changes substantially during typical maturation. We used resting-state magnetoencephalography (MEG) to examine developmental trajectories of cortical EI alterations with regional specificity in a large cross-sectional cohort (N = 172; 92 typically developing, 80 ASD; ages 6-32). Functional EI (fEI), derived from critical brain dynamics, was estimated across 500 cortical parcellations. Group-averaged fEI maps revealed broadly similar large-scale topographic patterns across groups. Age-stratified analyses revealed increased global fEI in childhood and decreased fEI in adolescence in ASD, with no evidence of a group difference in adulthood. Parcel-wise regressions identified a significant main effect of diagnosis in right dorsolateral prefrontal cortex, where typically developing individuals showed higher fEI across all ages. A significant group-by-age interaction in left inferior parietal cortex indicated diverging developmental trajectories. Finally, fEI in paracentral and precuneus regions was associated with the magnitude of ASD symptoms. These findings indicate that EI imbalance in ASD is neither globally distributed nor static, but expressed through regionally and developmentally specific differences, with relevance for ASD heterogeneity.

neuroscience↗

bioRxiv2025

Combined MEG and EEG suggest a limbic source network of the P3 in retrosplenial cortex, insula, and hippocampus

The event-related P3 is evoked by most task-relevant or salient stimuli, but its neural sources remain controversial. Here we reevaluate the role of hippocampus, unambiguously demonstrated in intracranial recordings, and retro-splenial cortex as sources of the P3 in magneto- and electroencephalography. Observers detected rare visual targets of a deviant shape and ignored rare non-targets of a deviant color. Source analysis was based on noise-normalized minimum-norm estimates in an individual, MRI-based source space. Critically, the cortical source space was extended to include the cornu ammonis of the hippocampus. Source analysis at the P3 peak showed strong sources in retrosplenial cortex and a weaker source in hippocampus. Activity in left somatosensory cortex was related to the button presses. Subsequent activity was observed in insula and anterior mid-cingulate cortex. Further simulation studies explored the spread of these sources and the plausibility of their combination to explain the data, and demonstrate that the combination of magneto- and electroencephalography increased the specificity of the source estimate. Overall, these data support an interpretation of the P3 as physiological indicator of activity in the limbic system for target and distractor stimuli.

neuroscience↗

bioRxiv2025

Decreased auditory cortical activations and altered long-range alpha-band connectivity characterize passive auditory spatial attention in ASD

Autism Spectrum Disorder (ASD) is a developmental condition characterized by difficulties in social interaction, communication and sensory processing. The ability to orient towards sounds is a key component of social interactions, yet auditory spatial attention remains relatively understudied in ASD, despite prior research indicating differences in this domain. Here, we investigate the neural signatures associated with passive auditory spatial attention in children with ASD (n = 21, ages 6-17) relative to age- and IQ-matched typically developing (TD) children (n = 31), using source-localized magnetoencephalography (MEG). Participants listened passively, while watching a silenced movie, to non-social auditory stimuli designed to either remain lateralized to one hemifield (stay trials), or to change in location from one side to the contralateral hemifield (jump trials). Linear mixed effects modeling showed lower cortical activation in the auditory cortex in the ASD group in response to jump trials, relative to the TD group. Additionally, functional connectivity analyses showed higher alpha-band functional connectivity in the ASD group between left auditory cortex seeds and right prefrontal and left parietal regions known to be recruited during auditory spatial attention. Right prefrontal alpha-band connectivity estimates were associated with behaviorally assessed auditory processing scores, whereas left parietal connectivity estimates were associated with ASD symptomatology. Our results align with the hypothesis that auditory spatial attention generally, and specifically orientation to sounds even when experienced passively, differs in ASD individuals.

neuroscience↗

bioRxiv2024

The Human Cerebellum: A Digital Anatomical Atlas at the Level of Individual Folia

Scientific interest in the cerebellum has surged in the last few decades with an emerging consensus on a multifaceted functionality and intricate, but not yet fully understood, functional topography over the cerebellar cortex. To further refine this structure-function relationship and quantify its inter-subject variability, a high-resolution digital anatomical atlas is fundamental. Using a combination of manual labeling and image processing, we turned a recently published reconstruction of the human cerebellum, the first such reconstruction fine enough to resolve the individual folia, into a digital atlas with both surface and volumetric representations. Its unprecedented granularity (0.16 mm) and detailed expert labeling make the atlas usable as an anatomical ground truth, enabling new ways of analyzing and visualizing cerebellar data through its digital format.

neuroscience↗

bioRxiv2023

A role for retro-splenial cortex in the task-related P3 network

ObjectiveThe P3 is an event-related response observed in relation to task-relevant sensory events. Despite its ubiquitous presence, the neural generators of the P3 are controversial and not well identified. MethodsWe compared source analysis of combined magneto- and electroencephalography (M/EEG) data with functional magnetic resonance imaging (fMRI) and simulation studies to better understand the sources of the P3 in an auditory oddball paradigm. ResultsOur results suggest that the dominant source of the classical, postero-central P3 lies in the retro-splenial cortex of the ventral cingulate gyrus. A second P3 source in the anterior insular cortex contributes little to the postero-central maximum. Multiple other sources in the auditory, somatosensory, and anterior midcingulate cortex are active in an overlapping time window but can be functionally dissociated based on their activation time courses. ConclusionThe retro-splenial cortex is a dominant source of the parietal P3 maximum in EEG. SignificanceThese results provide a new perspective for the interpretation of the extensive research based on the P3 response.

neuroscience↗

bioRxiv2022

Cortical dynamics following real-time MEG neurofeedback training of the speed of shifting spatial attention: a pilot study

Neurofeedback is a technique that directs self-regulated modulation of neural activity. This is achieved by delivering real-time feedback derived from brain signals. In our previous work, we introduced a novel method, state-based neurofeedback (sb-NFB) that targets patterns of MEG signals related to shifts in spatial attention. In this pilot study, we used sb-NFB to train participants to decrease the time required to covertly shift spatial attention from one visual hemifield to the other. We characterized the changes to cortical connectivity during each training session. In addition, we run a separate, Posner-like validation task before the training sessions and after the training was complete. We found a significant main effect of training on the reaction time linked to switching spatial attention in both the training task and the validation task. This indicates the achieved improvement in shifting spatial attention generalized to another situation requiring this capability.

neuroscience↗

bioRxiv2020

Automatic Reconstruction of Cerebellar Cortex from Standard MRI Using Diffeomorphic Registration of a High-Resolution Template (ARCUS)

As cumulating evidence points to a wider range of functional tasks and neurological conditions that involve the cerebellum than previously known, the interest for examining the cerebellum with non-invasive neuroimaging techniques is growing. However, the standard methods of computational neuroanatomy for segmenting and reconstructing the cerebral cortex work poorly for the cerebellar cortex at the resolutions attainable with contemporary MRI technology because of its extremely intricate folding, making detailed and topologically correct reconstructions of the geometry of the cerebellar cortical surface unfeasible. Recently, a detailed surface reconstruction of the human cerebellar cortex was achieved from an ex-vivo specimen. These novel anatomical data enable a new reconstruction technique where this detailed surface reconstruction is morphed to subject space based on standard in-vivo MRI data. The result is an approximate reconstruction of the cerebellar cortex that requires only standard-resolution MRI data and can be used e.g., in functional neuroimaging, for integrating topographic population data or for visualizing topographic data on flattened surface patches.

neuroscience↗

bioRxiv2017

Left-Lateralized Contributions of Saccades to Cortical Activity during a One-Back Word Recognition Task

Saccadic eye movements are an inherent component of natural reading, yet their contribution to information processing at subsequent fixation remains elusive. Here we use anatomically-constrained magnetoencephalography (MEG) to examine cortical activity following saccades as healthy human subjects engaged in a one-back word recognition task. This activity was compared with activity following external visual stimulation that mimicked saccades. A combination of procedures were employed to eliminate saccadic ocular artifacts from the MEG signal. Both saccades and saccade-like external visual stimulation produced early-latency responses beginning ~70 ms after onset in occipital cortex and spreading through the ventral and dorsal visual streams to temporal, parietal and frontal cortices. Robust differential activity following the onset of saccades versus similar external visual stimulation emerged during 150-350 ms in a left-lateralized cortical network. This network included (i) left lateral occipitotemporal and nearby inferotemporal cortex, (ii) left posterior Sylvian fissure and nearby multimodal cortex, and (iii) medial parietooccipital, posterior cingulate and retrosplenial cortices. Moreover, this left-lateralized network colocalized with word repetition priming effects. Together, results suggest that central saccadic mechanisms influence a left-lateralized language network in occipitotemporal and temporal cortex above and beyond saccadic influences at preceding stages of information processing during visual word recognition.

neuroscience↗