Biology subjects

Maki-Marttunen, V.

Publications and source records attributed to Maki-Marttunen, V..

6 recordsLinked to original sources

bioRxiv2025

Thalamic Nuclei Volumes Across Psychiatric and Neurological Disorders: A Multi-Site Magnetic Resonance Imaging Study

The human thalamus is an integrative hub for multiple cortical and subcortical circuits involved in sensory processing and higher cognitive functions. Thalamic volume differences have been reported across multiple psychiatric and neurological disorders, but previous studies have typically relied on small samples, focused on one or a limited number of disorders, or investigated the thalamus as a whole without considering its functional subdivisions. In this multi-site study, we compared thalamic nuclei volumes across mild cognitive impairment (MCI), dementia (DEM), major depressive disorder, schizophrenia spectrum disorder (SCZ), clinical high risk for schizophrenia, bipolar spectrum disorder, autism spectrum disorder, attention-deficit/hyperactivity disorder, Parkinsons disease, multiple sclerosis (MS), and healthy controls (N > 8 000). Using structural MRI, we segmented 25 bilateral thalamic nuclei, corresponding to six anatomical groups. Linear models revealed that anterior, medial and lateral regions of the thalamus were significantly smaller in several conditions, with largest effects observed for MCI, DEM, SCZ and MS. In contrast, the ventral and intralaminar groups were relatively normal. This pattern of effects largely corresponds to the canonical functional subdivision of the thalamus into higher-order and sensory regions. At the level of individual nuclei, the clinical conditions were associated with distinct patterns of alterations, while left and right lateral geniculate nuclei were implicated in six of the disorders, suggesting a possible relation with circadian and sleep disturbances. Together, the results highlight a role for the higher-order thalamus in common brain disorders and a differential involvement at the nuclei level, refining our understanding of thalamic pathology across common brain disorders.

neuroscience↗

bioRxiv2025

Neural correlates of image memorability: Combining large-scale 7T fMRI with machine learning-based predictions

We combine ultra-high-resolution fMRI with machine learning predictions to investigate the neural correlates of image memorability. Using ViTMem, a visual transformer-based tool, we estimated memorability scores for over 70,000 natural scenes from the NSD dataset. Our analyses reveal that higher memorability scores correlate with increased activation in ventral visual regions (fusiform gyrus, middle occipital cortex) and medial temporal areas (hippocampus, amygdala). Notably, we also observed significant engagement in fronto-parietal regions, indicating a broader network involved in modulating memory encoding. These novel findings demonstrate that ViTMem not only reliably predicts stimulus memorability but also provides a powerful framework for scalable investigations into the neural mechanisms underlying perceptual and mnemonic processes.

animal behavior and cognition↗

bioRxiv2024

Neuromodulatory influences on propagation of brain waves along the unimodal-transmodal gradient

Brain activity fluctuates over time, and understanding the factors that influence such fluctuations is important to understand the flexible nature of the brain and cognition. Growing evidence suggests that fMRI brain activity shows spatio-temporal patterns of propagation following specific gradients. In particular, activity around global peaks propagates as a travelling wave following a gradient from unimodal to associative areas. Some properties of these travelling waves seem to be related to behavioral and arousal states, however their meaning remains unknown. Here we assess the possibility that travelling waves explain the finding that there are specific time points when the brain presents larger brain integration. We reasoned that a faster speed of propagation would be related to more brain integration as measured with fMRI. Furthermore, we explored whether increased pupil-linked arousal, which has been related to more integration in specific brain regions, would be increased during periods of whole brain propagation. To test these hypotheses, we detected brain travelling waves and characterized them in terms of speed, directionality and ratio. We compared these features between different task conditions, and after a pharmacological challenge affecting neuromodulatory tone. We then studied the relation between travelling wave speed, pupil size and a graph-based measure of brain integration. Our results suggest that neuromodulatory tone affects travelling wave propagation, and that this propagation reflects changes in arousal and integrated functional connectivity features. This study provides a novel view of brain dynamics in terms of the effects of neruomodulatory influences across time scales.

neuroscience↗

bioRxiv2024

Strength of low-frequency phase entrainment to external stimuli is associated with fluctuations in the brain's internal states

The brain attends to environmental rhythms by aligning the phase of internal oscillations. However, the factors underlying fluctuations in the strength of this phase entrainment remain largely unknown. In the present study we examined whether the strength of low-frequency EEG phase entrainment to rhythmic stimulus sequences varied with pupil size and posterior alpha-band power, thought to reflect arousal level and excitability of posterior cortical brain areas, respectively. We recorded pupil size and scalp EEG while participants carried out an intermodal selective attention task, in which they were instructed to attend to a rhythmic sequence of visual or auditory stimuli and ignore the other perceptual modality. As expected, intertrial phase coherence (ITC), a measure of entrainment strength, was larger for the task-relevant than for the task-irrelevant modality. Across the experiment, pupil size and posterior alpha power were strongly linked with each other. Interestingly, ITC tracked both variables: larger pupil size was associated with a selective increase in entrainment to the task-relevant stimulus sequence, whereas larger posterior alpha power was associated with a decrease in phase entrainment to both the task-relevant and task-irrelevant stimulus sequences. Exploratory analyses showed that a temporal relation between ITC and posterior alpha power emerged in the time periods around pupil maxima and pupil minima. These results indicate that endogenous sources contribute distinctly to the fluctuations of EEG phase entrainment. Significance statementFluctuations in cortical state powerfully shape the perception of external stimuli. Understanding the physiological signatures of cortical state fluctuations is crucial to understand how the brain selectively attends and switches between internal and external content. Here we studied how two signatures of attentional state, pupil-linked arousal and power in the alpha band, shape the entrainment of brain activity to low-frequency rhythmic stimuli. Our results reveal common and dissociable influences of these signatures at slow time scales. Furthermore, measuring and including pupil size and posterior alpha power as covariates in statistical models can help increase statistical power in studies focusing on EEG phase entrainment. Our study provides new evidence on a direct influence of cortical state on the perception of rhythmic stimuli.

animal behavior and cognition↗

bioRxiv2022

Assessing pupil size as an index of activation of subcortical ascending arousal system nuclei during rest

Neuromodulatory nuclei that are part of the ascending arousal system (AAS) play a crucial role in regulating cortical state and optimizing task performance. Pupil diameter, under constant luminance conditions, is increasingly used as an index of activity of these AAS nuclei. Indeed, task-based functional imaging studies in humans have begun to provide evidence of stimulus-driven pupil-AAS coupling. However, whether there is such a tight pupil-AAS coupling during rest is not clear. To address this question, we examined simultaneously acquired resting-state fMRI and pupil-size data from 74 participants, focusing on six AAS nuclei: the locus coeruleus, ventral tegmental area, substantia nigra, dorsal and median raphe nuclei, and cholinergic basal forebrain. Activation in all six AAS nuclei was optimally correlated with pupil size at 0-to 2-second lags, suggesting that spontaneous pupil changes were almost immediately followed by corresponding BOLD-signal changes in the AAS. These results suggest that spontaneous changes in pupil size that occur during states of rest can be used as a noninvasive general index of activity in AAS nuclei. Importantly, the nature of pupil-AAS coupling during rest appears to be vastly different from the relatively slow canonical hemodynamic response function that has been used to characterize task-related pupil-AAS coupling.

neuroscience↗

bioRxiv2018

Distinct neural mechanisms meet challenges in dynamic visual attention due to either load or spatial interference

When solving dynamic visuo-spatial tasks, the brain copes with perceptual and cognitive processing challenges. In the multiple-object tracking (MOT) task, the number of objects to be tracked (i.e. load) imposes attentional demands, but so does spatial interference from irrelevant objects (i.e. crowding). Presently, it is not clear whether load and crowding activate separate cognitive and physiological mechanisms. Such knowledge would be important to understand the neurophysiology of visual attention. Furthermore, it would help resolve conflicting views between theories of visual cognition, particularly concerning sources of capacity limitations. To address this problem, we varied the degree of processing challenge in the MOT task in two ways: First, the number of objects to track, and second, the spatial proximity between targets and distractors. We first measured task-induced pupil dilations and saccades during MOT. In a separate cohort we measured fMRI brain activity during MOT. The behavioral results in both cohorts revealed that increased load and crowding led to reduced accuracy in an additive manner. Load was associated with pupil dilations, whereas crowding was not. Activity in dorsal attentional areas and frequency of saccades were proportionally larger both with higher levels of load and crowding. Higher crowding recruited additionally ventral attentional areas that may reflect orienting mechanisms. The activity in the brainstem nuclei ventral tegmental area/substantia nigra and locus coeruleus showed clearly dissociated patterns. Our results constitute convergent evidence from independent samples that processing challenges due to load and object spacing may rely on different mechanisms.

neuroscience↗