Theta Phase-dependent Modulation of Perception by Concurrent Transcranial Alternating Current Stimulation and Periodic Visual Stimulation

Background: Sensory perception can be modulated by the phase of neural oscillations, especially in the theta and alpha ranges. Oscillatory activity in the visual cortex can be entrained by transcranial alternating current stimulation (tACS) as well as periodic visual stimulation (i.e., flicker). Combined tACS and visual flicker stimulation modulates blood- oxygen-level-dependent (BOLD) responses and concurrent 4 Hz auditory click-trains and tACS modulates auditory perception in a phase-dependent way. Objective: In the present study, we investigated if phase synchrony between concurrent tACS and periodic visual stimulation (i.e., flicker) can modulate performance on a visual matching task. Methods: Participants completed a visual matching task on a flickering visual stimulus while receiving either in-phase (0°) or asynchronous (180°, 90°, or 270°) tACS at alpha or theta frequency. Stimulation was applied over either occipital cortex or dorsolateral prefrontal cortex (DLPFC). Results: Visual performance was significantly better during theta frequency tACS over the visual cortex when it was in-phase (0°) with visual stimulus flicker, compared to anti-phase (180°). This effect did not appear with alpha frequency flicker or with DLPFC stimulation. Furthermore, a control sham group showed no effect. There were no significant performance differences amongst the asynchronous (180°, 90°, and 270°) phase conditions. Conclusion: Extending previous studies on visual and auditory perception, our results support a crucial role of oscillatory phase in sensory perception and demonstrate a behaviourally relevant combination of visual flicker and tACS. The spatial and frequency specificity of our results have implications for research on the functional organisation of perception

Transcranial alternating current stimulation (tACS) at 40 Hz enhances face and object perception

Neurophysiological evidence suggests that face and object recognition relies on the coordinated activity of neural populations (i.e., neural oscillations) in the gamma-band range (> 30 Hz) over the occipito-temporal cortex. To test the causal effect of gamma-band oscillations on face and object perception we applied transcranial Alternating Current Stimulation (tACS) in healthy volunteers (N = 60). In this single-blind, sham-controlled study, we examined whether the administration of offline tACS at gamma-frequency (40 Hz) over the right occipital cortex enhances performance of perception and memory of face and object stimuli. We hypothesized that gamma tACS would enhance the perception of both categories of visual stimuli. Results, in line with our hypothesis, show that 40 Hz tACS enhanced both face and object perception. This effect is process-specific (i.e., it does not affect memory), frequency-specific (i.e., stimulation at 5 Hz did not cause any behavioural change), and site-specific (i.e., stimulation of the sensory-motor cortex did not affect performance). Our findings show that high-frequency tACS modulates human visual perception, and it is in line with neurophysiological studies showing that the perception of visual stimuli (i.e., faces and objects) is mediated by oscillations in the gamma-band range. Furthermore, this study adds insight about the design of effective neuromodulation protocols that might have implications for interventions in clinical settings

Magnetoencephalography in cognitive neuroscience: a primer

Magnetoencephalography (MEG) is an invaluable tool to study the dynamics and connectivity of large-scale brain activity and their interactions with the body and the environment in functional and dysfunctional body and brain states. This primer introduces the basic concepts of MEG, discusses its strengths and limitations in comparison to other brain imaging techniques, showcases interesting applications, and projects exciting current trends into the near future, in a way that might more fully exploit the unique capabilities of MEG

Manipulating neuronal communication by using low-intensity repetitive transcranial magnetic stimulation combined with electroencephalogram

Repetitive transcranial magnetic stimulation (rTMS) modulates ongoing brain rhythms by activating neuronal structures and evolving different neuronal mechanisms. In the current work, the role of stimulation strength and frequency for brain rhythms was studied. We hypothesized that a weak oscillating electric field induced by low-intensity rTMS could induce entrainment effects in the brain. To test the hypothesis, we conducted three separate experiments, in which we stimulated healthy human participants with rTMS. We individualized stimulation parameters using computational modeling of induced electric fields in the targets and individual frequency estimated by electroencephalography (EEG). We demonstrated the immediately induced entrainment of occipito-parietal and sensorimotor mu-alpha rhythm by low-intensity rTMS that resulted in phase and amplitude changes measured by EEG. Additionally, we found long-lasting corticospinal excitability changes in the motor cortex measured by motor evoked potentials from the corresponding musle.2021-11-2

Encoding and recall of memory for reward location in the mouse hippocampus

The memory of where to find food can be crucial for an animal’s survival. Encoding and recall of these spatial memories involves the hippocampus, but whether and how hippocampal activity integrates memories of spatial relationships and locations is poorly understood. This thesis investigates how hippocampal activity facilitates the encoding of reward memories and how this encoding shapes hippocampal activity during memory recall in mice learning reward locations. Encoding of memory happens in stages that depend on the hippocampal state. The thesis interrogated how two different hippocampal states, one during movement and the other during reward consumption, are affected by acetylcholine – a neuromodulator released predominantly during movement and exploration. The findings highlight how acetylcholine modulates hippocampal state and how, when experimentally altered, it can impede memory encoding. Hippocampal activity facilitates navigation towards the learned reward locations. Individual neurons fire at specific locations of the environment, and, collectively, they cover the environment forming its cognitive map. To answer how the hippocampal activity could encode a memory of reward location, the thesis investigated how these spatial representations and the population activity change after learning. I found that the reward memory shapes the activity in the dorsal CA1 of the hippocampus by modulating its overall population activity and in the intermediate CA1 by modulating the activity of a reward-specific cell population. Together, these results suggest how hippocampal activity could facilitate encoding and recall of memory for reward locations

Inattentional Blindness: Neural Correlates and Theoretical Progress

Consciousness has remained one of the most perplexing enigmas of science and philosophy. Modern neuroscientific research seeks to understand how consciousness emerges within biological systems through identifying the necessary mechanisms that enable sensory information to be consciously experienced. Inattentional blindness (IB), the failure to notice something right in front of you, offers a profound means of studying consciousness, as it highlights the indistinct boundary between the conscious and the unconscious. The primary goal of the current thesis was to contribute to a scientific understanding of consciousness through advancing knowledge on IB. To this end, two reviews and four empirical studies were conducted. The first review provides a qualitative synthesis of empirical literature on IB that has employed neuroscientific methodology. Findings suggest that neural correlates of consciousness under conditions of IB may favour early sensory views of consciousness, however more research is needed. The second review provides a systematic review of the behavioural literature on IB, with focus on its two leading theories. Findings highlight that no theory can yet fully account for IB, and a model of IB is proposed based on the partial awareness hypothesis. Study one investigates the relation between alpha-band neural activity and IB via electroencephalography (EEG). Results indicate that a reduction in alpha activity in the pre- and post-stimulus interval correlates with consciousness of the critical stimulus during IB. Study two employs transcranial alternating current stimulation (tACS) to examine a causal role of alpha activity in IB. Findings indicate that, relative to control conditions, those stimulated at alpha frequency were more likely to be subject to IB. Study three extends on study two by implementing auditory tone trains at various frequencies during IB. Results show no difference in rates of IB based on auditory tone frequency. Study four then addresses the degree to which semantic processing, as indexed via the N400, can occur under conditions of IB. Findings show that no significant N400 activity is observed when the eliciting stimuli are rendered unconscious via IB. Overall, the implications of the current thesis are that alpha activity has a reliable, and potentially causal, relationship with IB; that a coherent explanation of IB is yet to exist, but may be found in reconsidering the traditional view of visual consciousness more broadly; and that the endowment of meaning to sensory information may be a key function of consciousness

The thalamocortical symphony:How thalamus and cortex play together in schizophrenia and plasticity

The work presented in this thesis aimed at investigating the function and mechanism of corticothalamic-thalamocortical network in schizophrenia and experience-dependent plasticity, further discussed their possible connection.In Chapter 2, we examined the effects of low-dose ketamine on the corticothalamic circuit (CTC) system. Our findings reveal that ketamine induces abnormal spindle activity and gamma oscillations in the CTC system. Notably, ketamine also leads to a transition in thalamic neurons from burst-firing to tonic action potential mode, which may underlie deficits in spindle oscillations. Chapter 3 addresses sensory perception deficits in schizophrenia, emphasizing disruptions in beta and gamma frequency oscillations due to signal-to-noise ratio imbalances. Chapter 4 explores experience-dependent plasticity, highlighting the role of thalamic synaptic inhibition in ocular dominance plasticity and the influence of cortical feedback. Chapter 5 investigates the involvement of endocannabinoids, particularly CB1 receptors, in inhibitory synaptic maturation and ocular dominance plasticity within the primary visual cortex.The general discussion raises the possibility of a link between neural plasticity and schizophrenia, particularly during the transformative phase of adolescence when the brain undergoes significant changes. An abnormal balance between inhibition and excitation, influenced by GABAergic maturation deficits, connectivity disruptions, and altered perceptual information transfer, may contribute to the development of schizophrenia.This thesis offers valuable insights into the intricate mechanisms underlying schizophrenia, with a particular focus on the CTC circuit, NMDA receptors, and endocannabinoids in the context of neuronal plasticity and cognitive function