Biology subjects

De Lucia, M.

Publications and source records attributed to De Lucia, M..

3 recordsLinked to original sources

bioRxiv2022

Single-subject EEG measurement of interhemispheric transfer-time for the in-vivo estimation of axonal morphology

Assessing axonal morphology in-vivo opens new avenues for the combined study of brain structure and function. A novel approach has recently been introduced to estimate the morphology of axonal fibers from the combination of MRI data and EEG measures of the interhemispheric transfer time (IHTT). In the original study, the IHTT measures were computed from EEG data averaged across a group, leading to bias of the axonal morphology estimates. Here, we seek to estimate axonal morphology from individual measures of IHTT, obtained from EEG data acquired in a visual evoked potential experiment. Subject-specific IHTTs are computed in a data-driven framework with minimal a priori constraints, based on the maximal peak of neural responses to visual stimuli within periods of statistically significant evoked activity in the inverse solution space. The subject-specific IHTT estimates ranged from 8 to 29 ms except for one participant and the between-session variability was comparable to the differences in IHTT between subjects. The scale parameter of the axonal radius distribution, computed from the IHTT estimates and the MRI data, ranged from 0 to 0.79 m. The change in axonal g-ratio with axonal radius ranged from 0.62 to 0.81 m-. The single-subject measurement of the IHTT yields estimates of axonal morphology that are consistent with histological values. However, improvement of the repeatability of the IHTT estimates is required to improve the specificity of the single-subject axonal morphology estimates.

neuroscience↗

bioRxiv2022

Cardio-audio synchronization elicits prediction in auditory sequences during human wakefulness and sleep

The human brain can infer temporal regularities in auditory sequences with fixed sound-to-sound intervals and in pseudo-regular sequences where sound onsets are locked to cardiac inputs. Here, we investigated auditory and cardio-audio regularity encoding during sleep, when reduced vigilance may result in altered bodily and environmental stimulus processing. Using electroencephalography and electrocardiography in healthy volunteers (N=26) during wakefulness and sleep, we measured the response to unexpected sound omissions within three auditory regularity conditions: synchronous, where sound and heartbeat are temporally locked, isochronous, with fixed sound-to-sound intervals, and a control condition without specific regularity. During wakefulness and all sleep stages, the cardiac signal following sound omissions exhibited a deceleration over time in the synchronous condition only. At the neural level, both the synchronous and isochronous sequences gave rise to a neural omission response in wakefulness and N2 sleep. Regularity encoding in the synchronous and isochronous conditions was characterized by a modulation of the background oscillatory activity in N2 sleep, outlining a possible mechanism through which the brain aligns periods of high neuronal excitability to the expected sound onset. The violation of auditory and cardio-audio regularity elicits cardiac and neural surprise responses across vigilance stages. Significance StatementAcross vigilance states, the human brain can generate predictions about the future based on past sensory regularities. While this is evident for environmental stimuli, the role of bodily signals in forming sensory prediction remains unknown. Here, we show that the human brain utilizes the temporal relationship between cardiac and auditory inputs in order to anticipate upcoming sounds during wakefulness and sleep. After presenting sounds in synchrony with the ongoing heartbeat, a sound omission elicited both a heartbeat deceleration and a prediction error signal as measured by the electroencephalographic response. Heartbeat signals support auditory regularity encoding during sleep and wakefulness, highlighting one mechanism for optimizing the detection of unexpected stimuli by taking advantage of the continuously monitored cardiac signals.

neuroscience↗

bioRxiv2022

In-vivo estimation of axonal morphology from MRI and EEG data

PurposeWe present a novel approach that allows the estimation of morphological features of axonal fibers from data acquired in-vivo in humans. This approach allows the assessment of white matter microscopic properties non-invasively with improved specificity. TheoryThe proposed approach is based on a biophysical model of Magnetic Resonance Imaging (MRI) data and of axonal conduction velocity estimates obtained with Electroencephalography (EEG). In a white matter tract of interest, these data depend on 1) the distribution of axonal radius - P(r)- and 2) the g-ratio of the individual axons that compose this tract - g(r). P(r)is assumed to follow a Gamma distribution with mode and scale parameters, M and{theta} , and g(r) is described by a power-law with parameters and {beta}. MethodsMRI and EEG data were recorded from 14 healthy volunteers. MRI data were collected with a 3T scanner. MRI g-ratio maps were computed and sampled along the visual transcallosal tract. EEG data were recorded using a 128-lead system with a visual Poffenberg paradigm. The interhemispheric transfer time and axonal conduction velocity were computed from the EEG current density at the group level. Using the MRI and EEG measures and the proposed model, we estimated morphological properties of axons in the visual transcallosal tract. ResultsThe estimated interhemispheric transfer time was 11.72{+/-}2.87 ms, leading to an average conduction velocity across subjects of 13.22{+/-}1.18 m/s. Out of the 4 free parameters of the proposed model, we estimated{theta} - the width of the right tail of the axonal radius distribution and {beta} - the scaling factor of the axonal g-ratio, a measure of fiber myelination. Across subjects, the parameter{theta} was 0.40{+/-}0.07 {micro}m and the parameter {beta} was 0.67{+/-}0.02 {micro}m-. ConclusionsThe estimates of axonal radius and myelination are consistent with histological findings, illustrating the feasibility of this approach. The proposed method allows the measurement of the distribution of axonal radius and myelination within a white matter tract, opening new avenues for the combined study of brain structure and function, and for in-vivo histological studies of the human brain.

neuroscience↗