Biology subjects

Alaerts, K.

Publications and source records attributed to Alaerts, K..

6 recordsLinked to original sources

bioRxiv2021

Multimodal lesion network mapping to predict sensorimotor behavior in stroke patients

Lesion network mapping (LNM) has proved to be a successful technique to map symptoms to brain networks after acquired brain injury. Beyond the characteristics of a lesion, such as its etiology, size or location, LNM has shown that common symptoms in patients after injury may reflect the effects of their lesions on the same circuits, thereby linking symptoms to specific brain networks. Here, we extend LNM to its multimodal form, using a combination of functional and structural connectivity maps drawn from data from 1000 healthy participants in the Human Connectome Project. We applied the multimodal LNM to a cohort of 54 stroke patients with the aim of predicting sensorimotor behavior, as assessed through a combination of motor and sensory tests. Test scores were predicted using a Canonical Correlation Analysis with multimodal brain maps as independent variables, and cross-validation strategies were employed to overcome overfitting. The results obtained led us to draw three conclusions. First, the multimodal analysis reveals how functional connectivity maps contribute more than structural connectivity maps in the optimal prediction of sensorimotor behavior. Second, the maximal association solution between the behavioral outcome and multimodal lesion connectivity maps suggests an equal contribution of sensory and motor coefficients, in contrast to the unimodal analyses where the sensory contribution dominates in both structural and functional maps. Finally, when looking at each modality individually, the performance of the structural connectivity maps strongly depends on whether sensorimotor performance was corrected for lesion size, thereby eliminating the effect of larger lesions that produce more severe sensorimotor dysfunction. By contrast, the maps of functional connectivity performed similarly irrespective of any correction for lesion size. Overall, these results support the extension of LNM to its multimodal form, highlighting the synergistic and additive nature of different types of imaging modalities, and the influence of their corresponding brain networks on behavioral performance after acquired brain injury.

neuroscience↗

bioRxiv2021

The EEG spectral fingerprints of meditation and mind wandering differ between experienced meditators and novices

Previous literature suggests that meditation training is associated with changes in participants experience during meditation practice. In this study, we assess whether putative differences in the experience of meditation between meditators and non-meditators are reflected in EEG spectral modulations. For this purpose, we recorded electroencephalography (EEG) during rest and two breath focus meditations (with and without experience sampling) in a group of 29 adult participants with more than 3 years of meditation experience and a control group of 29 participants without any meditation experience. Experience sampling in one of the meditation conditions allowed us to disentangle periods of breath focus from mind wandering (i.e. moments of distraction driven by task-irrelevant thoughts) during meditation practice. Overall, meditators reported a greater level of focus and reduced mind wandering during meditation practice than controls. In line with these reports, EEG spectral modulations associated to meditation and mind wandering also differed significantly between meditators and controls. While meditators (but not controls) showed a significant decrease in individual alpha frequency and amplitude and a steeper 1/f slope during meditation relative to rest, controls (but not meditators) showed a relative increase in individual alpha amplitude during mind wandering relative to breath focus periods. Together, our results show that the experience of meditation changes with training and that this is reflected in oscillatory and non-oscillatory components of brain activity.

neuroscience↗

bioRxiv2020

EEG alpha-theta dynamics during mind wandering in the context of breath focus meditation: an experience sampling approach with novice meditation practitioners

Meditation practice entails moments of distraction dominated by self-generated thoughts (i.e. mind wandering). Initial studies assessing the neural correlates of mind wandering in the context of meditation practice have identified an important role of theta (4-8 Hz) and alpha (8-14 Hz) neural oscillations. In this study, we use a probe-caught experience sampling paradigm to assess spectral changes in the theta-alpha frequency range during mind wandering in the context of breath focus meditation. Electroencephalography (EEG) was measured in 25 novice meditation practitioners during a breath focus task in which they were repeatedly probed to report whether they were focusing on their breath or thinking about something else. Mind wandering episodes were associated with an increase in the amplitude and a decrease in the frequency of theta (4-8 Hz) oscillations. Conversely, alpha oscillations (8-14 Hz) were shown to decrease in amplitude and increase in frequency during mind wandering relative to breath focus. In addition, mind wandering episodes were shown to be accompanied by increased harmonicity and phase synchrony between alpha and theta rhythms. Because similar spectral changes in the theta-alpha frequency range have been reported during controlled cognitive processes involving memory and executive control, we speculate that mind wandering and controlled processes could share some neurocognitive mechanisms. From a translational perspective, this study indicates that oscillatory activity in the theta-alpha frequency range could form adequate parameters for developing EEG-neurofeedback protocols aimed at facilitating the detection of mind wandering during meditation practice.

neuroscience↗

bioRxiv2020

Enhanced mirroring upon mutual gaze: Multimodal evidence from TMS-assessed corticospinal excitability and the EEG mu rhythm

Eye-to-eye contact is a salient cue for regulating everyday social interaction and communication. Previous research has demonstrated that direct eye contact between actor and observer specifically enhances the mirroring of others actions in the observer, as measured by transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs; an index of motor cortex excitability during action observation). However, it remains unknown whether other markers of mirror system activation, such as suppression of the EEG mu rhythm (i.e. attenuation of neural oscillations in the 8-13 Hz frequency band over the sensorimotor strip), are also susceptible to perceived eye contact. In the current study, a multimodal approach was adopted to assess both TMS-induced MEPs and EEG mu suppression (in separate sessions), while 32 participants (20 men; mean age: 24;8 years) observed a simple hand movement in combination with direct or averted gaze from the live stimulus person. Both indices of mirror system functioning were significantly modulated by perceived eye gaze; showing a significant increase in MEP amplitude and a significant attenuation of the mu rhythm when movement observation was accompanied with direct compared to averted gaze. Importantly, while inter-individual differences in absolute MEP and mu suppression scores were not significantly related, a significant association was identified between gaze-related changes in MEP responses and mu suppression. As such, it appears that while the neurophysiological substrates underlying mu suppression and TMS-induced MEP responses differ, both are similarly affected by the modulatory impact of gaze-related cues. In sum, our results suggest that both EEG mu rhythm and TMS-induced MEPs are sensitive to the social relevance of the observed actions, and that a similar neural substrate may drive gaze-related changes in these distinct markers of mirror system functioning.

neuroscience↗

bioRxiv2020

From thoughtless awareness to effortful cognition: alpha - theta cross-frequency dynamics in experienced meditators during meditation, rest and arithmetic

Neural activity is known to oscillate within discrete frequency bands and the synchronization between these rhythms is hypothesized to underlie information integration in the brain. Since strict synchronization is only possible for harmonic frequencies, a recent theory proposes that the interaction between different brain rhythms is facilitated by transient harmonic frequency arrangements. In this line, it has been recently shown that the transient occurrence of 2:1 harmonic cross-frequency relationships between alpha and theta rhythms (i.e. falpha{approx}12 Hz; ftheta{approx}6 Hz) is enhanced during effortful cognition. In this study, we tested whether achieving a state of mental emptiness during meditation is accompanied by a relative decrease in the occurrence of 2:1 harmonic cross-frequency relationships between alpha and theta rhythms. Continuous EEG recordings (19 electrodes) were obtained from 43 highly experienced meditators during meditation practice, rest and an arithmetic task. We show that the occurrence of transient alpha:theta 2:1 harmonic relationships increased linearly from a meditative to an active cognitive processing state (i.e. meditation< rest< arithmetic task). It is argued that transient EEG cross-frequency arrangements that prevent alpha:theta cross-frequency coupling could facilitate the experience of mental emptiness by avoiding the interaction between the memory and executive components of cognition.

neuroscience↗

bioRxiv2019

Sensorimotor functional connectivity in unilateral cerebral palsy: influence of corticospinal tract wiring pattern and clinical correlates

In children with unilateral cerebral palsy (uCP), the corticospinal tract (CST) wiring patterns may differ (contralateral, ipsilateral or bilateral), partially determining motor deficits. However, the impact of such CST wiring on functional connectivity remains unknown. Here, we explored differences in functional connectivity of the resting-state sensorimotor network in 26 uCP with periventricular white matter lesions (mean age (SD): 12.87m (4.5), CST wiring: 9 contralateral, 9 ipsilateral, 6 bilateral) compared to 60 healthy controls (mean age (SD): 14.54 (4.8)), and between CST wiring patterns. Functional connectivity from each M1 to three bilateral sensorimotor regions of interest (primary sensory cortex, dorsal and ventral premotor cortex) and the supplementary motor area was compared between groups (healthy controls vs. uCP; and healthy controls vs. each CST wiring group). Results from the seed-to-voxel analyses from bilateral M1 were compared between groups. Additionally, relations with upper limb motor deficits were explored. Aberrant sensorimotor functional connectivity seemed to be CST-dependent rather than specific from all the uCP population: in the dominant hemisphere, the contralateral CST group showed increased connectivity between M1 and premotor cortices, whereas the bilateral CST group showed higher connectivity between M1 and somatosensory association areas. These results suggest that functional connectivity of the sensorimotor network is CST wiring-dependent, although the impact on upper limb function remains unclear.

neuroscience↗