Reduced connectivity of primary auditory and motor cortices during exposure to auditory white noise

Sedative Effect of White Noise on Prefrontal Cortex Lobe: A Randomized Controlled Study Based on Functional Near-Infrared Spectroscopy

BACKGROUND

White noise has attracted widespread attention due to its potential effects on psychological and physiological states, particularly in promoting relaxation. The prefrontal cortex, a critical region of the brain responsible for higher cognitive functions and emotional regulation, may influence an individual's mental and physical health through its responses to external stimuli. Although previous research has investigated the calming effects of white noise, systematic studies on its specific impact on prefrontal cortex activity are still lacking. This study aims to explore the calming effects of white noise on the prefrontal cortex to elucidate its associated physiological mechanisms.

METHODS

In total, 103 healthy adult college students were recruited and randomly divided into four groups (fire, n = 24; wind, n = 27; rain, n = 27; and snow, n = 25), with each group exposed to the corresponding white noise for 3 min. Functional near-infrared spectroscopy (fNIRS) was used to evaluate excitability changes in the brain and changes in life signs and facial expressions were also measured.

RESULTS

The data of fNIRS were analyzed by paired sample t-test; in the wind group and the snow group, we found that the white noise can be effectively decreased the cortical excitability of related brain areas. The areas of reduced excitability were concentrated in the prefrontal cortex and pars triangularis of Broca's frontopolar area, while the concentration of oxyhemoglobin in these two area decreased from -0.159 to -0.107 µmol/L and from -0.139 to -0.096 µmol/L, respectively, both areas involved in relaxing and sedative modulation.

CONCLUSION

White noise can reduce the excitability of the prefrontal cortex and play a sedative effect. It may strengthen our understanding of how white noise is involved in neural modulation.

Assessing cortical excitability with electroencephalography: A pilot study with EEG-iTBS

BACKGROUND

Cortical excitability measures neural reactivity to stimuli, usually delivered via Transcranial Magnetic Stimulation (TMS). Excitation/inhibition balance (E/I) is the ongoing equilibrium between excitatory and inhibitory activity of neural circuits. According to some studies, E/I could be estimated in-vivo and non-invasively through the modeling of electroencephalography (EEG) signals and termed 'intrinsic excitability' measures. Several measures have been proposed (phase consistency in the gamma band, sample entropy, exponent of the power spectral density 1/f curve, E/I index extracted from detrend fluctuation analysis, and alpha power). Intermittent theta burst stimulation (iTBS) of the primary motor cortex (M1) is a non-invasive neuromodulation technique allowing controlled and focal enhancement of TMS cortical excitability and E/I of the stimulated hemisphere.

OBJECTIVE

Investigating to what extent E/I estimates scale with TMS excitability and how they relate to each other.

METHODS

M1 excitability (TMS) and several E/I estimates extracted from resting state EEG recordings were assessed before and after iTBS in a cohort of healthy subjects.

RESULTS

Enhancement of TMS M1 excitability, as measured through motor-evoked potentials (MEPs), and phase consistency of the cortex in high gamma band correlated with each other. Other measures of E/I showed some expected results, but no correlation with TMS excitability measures or strong consistency with each other.

CONCLUSIONS

EEG E/I estimates offer an intriguing opportunity to map cortical excitability non-invasively, with high spatio-temporal resolution and with a stimulus independent approach. While different EEG E/I estimates may reflect the activity of diverse excitatory-inhibitory circuits, spatial phase synchrony in the gamma band is the measure that best captures excitability changes in the primary motor cortex.

Functional ultrasound reveals effects of MRI acoustic noise on brain function

Loud acoustic noise from the scanner during functional magnetic resonance imaging (fMRI) can affect functional connectivity (FC) observed in the resting state, but the exact effect of the MRI acoustic noise on resting state FC is not well understood. Functional ultrasound (fUS) is a neuroimaging method that visualizes brain activity based on relative cerebral blood volume (rCBV), a similar neurovascular coupling response to that measured by fMRI, but without the audible acoustic noise. In this study, we investigated the effects of different acoustic noise levels (silent, 80 dB, and 110 dB) on FC by measuring resting state fUS (rsfUS) in awake mice in an environment similar to fMRI measurement. Then, we compared the results to those of resting state fMRI (rsfMRI) conducted using an 11.7 Tesla scanner. RsfUS experiments revealed a significant reduction in FC between the retrosplenial dysgranular and auditory cortexes (0.56 ± 0.07 at silence vs 0.05 ± 0.05 at 110 dB, p=.01) and a significant increase in FC anticorrelation between the infralimbic and motor cortexes (-0.21 ± 0.08 at silence vs -0.47 ± 0.04 at 110 dB, p=.017) as acoustic noise increased from silence to 80 dB and 110 dB, with increased consistency of FC patterns between rsfUS and rsfMRI being found with the louder noise conditions. Event-related auditory stimulation experiments using fUS showed strong positive rCBV changes (16.5% ± 2.9% at 110 dB) in the auditory cortex, and negative rCBV changes (-6.7% ± 0.8% at 110 dB) in the motor cortex, both being constituents of the brain network that was altered by the presence of acoustic noise in the resting state experiments. Anticorrelation between constituent brain regions of the default mode network (such as the infralimbic cortex) and those of task-positive sensorimotor networks (such as the motor cortex) is known to be an important feature of brain network antagonism, and has been studied as a biological marker of brain disfunction and disease. This study suggests that attention should be paid to the acoustic noise level when using rsfMRI to evaluate the anticorrelation between the default mode network and task-positive sensorimotor network.