Spontaneous blink-related beta power increase and theta phase reset in subthalamic nucleus of Parkinson patients during walking.

OBJECTIVE: Both blinking and walking are altered in Parkinson's disease and both motor outputs have been shown to be linked in healthy subjects. Additionally, studies suggest an involvement of basal ganglia activity and striatal dopamine in blink generation. We investigated the role of the basal ganglia circuitry on spontaneous blinking and if this role is dependent on movement state and striatal dopamine. METHODS: We analysed subthalamic nucleus (STN) activity in seven chronically implanted patients for deep brain stimulation (DBS) with respect to blinks and movement state (resting state and unperturbed walking). Neurophysiological recordings were combined with individual molecular brain imaging assessing the dopamine reuptake transporter (DAT) density for the left and right striatum separately. RESULTS: We found a significantly higher blink rate during walking compared to resting. The blink rate during walking positively correlated with the DAT density of the left caudate nucleus. During walking only, spontaneous blinking was followed by an increase in the right STN beta power and a bilateral subthalamic phase reset in the low frequencies. The right STN blink-related beta power modulation correlated negatively with the DAT density of the contralateral putamen. The left STN blink-related beta power correlated with the DAT density of the putamen in the less dopamine-depleted hemisphere. Both correlations were specific to the walking condition and to beta power following a blink. CONCLUSION: Our findings show that spontaneous blinking is related to striatal dopamine and has a frequency specific deployment in the STN. This correlation depends on the current movement state such as walking. SIGNIFICANCE: This work indicates that subcortical activity following a motor event as well as the relationship between dopamine and motor events can be dependent on the motor state. Accordingly, disease related changes in brain activity should be assessed during natural movement.

Reduced occipital alpha power marks a movement induced state change that facilitates creative thinking.

Walking and minimized movement restriction has a positive effect on creativity, such as divergent thinking. Walking is further known to reduce occipital alpha activity. We used mobile EEG during free and restricted movement, while subjects (N = 23) solved a Guilford's alternate uses test, to understand if occipital alpha power is also affected by movement restriction and if it is a neural marker for creativity. We found that, independent of the task, relative occipital alpha power was higher during movement restriction and showed a negative relationship with creativity scores even though the task was purely based on auditory information. Alpha lateralization was only modulated during the task related think-time (mainly during sitting) and showed a positive relationship with creativity scores but no correlation with the relative alpha power. This indicates that the ongoing alpha power and alpha lateralization mark two independent processes. Overall, our work shows that movement and movement restriction leads to a general change in state which affects cognitive processes. Specifically, limiting one's movements e.g. due to sitting and fixating on a screen can introduce a state of increased occipital alpha power and lowered creativity.

Effects of vocal demands on pupil dilation.

Pupil dilation is known to be affected by a variety of factors, including physical (e.g., light) and cognitive sources of influence (e.g., mental load due to working memory demands, stimulus/response competition etc.). In the present experiment, we tested the extent to which vocal demands (speaking) can affect pupil dilation. Based on corresponding preliminary evidence found in a reanalysis of an existing data set from our lab, we setup a new experiment that systematically investigated vocal response-related effects compared to mere jaw/lip movement and button press responses. Conditions changed on a trial-by-trial basis while participants were instructed to keep fixating a central cross on a screen throughout. In line with our prediction (and previous observation), speaking caused the pupils to dilate strongest, followed by nonvocal movements and finally a baseline condition without any vocal or muscular demands. An additional analysis of blink rates showed no difference in blink frequency between vocal and baseline conditions, but different blink dynamics. Finally, simultaneously recorded electromyographic activity showed that muscle activity may contribute to some (but not all) aspects of the observed effects on pupil size. The results are discussed in the context of other recent research indicating effects of perceived (instead of executed) vocal action on pupil dynamics.

Spontaneous local alpha oscillations predict motion-induced blindness.

Bistable visual illusions are well suited for exploring the neuronal states of the brain underlying changes in perception. In this study, we investigated oscillatory activity associated with 'motion-induced blindness' (MIB), which denotes the perceptual disappearance of salient target stimuli when a moving pattern is superimposed on them (Bonneh et al., ). We applied an MIB paradigm in which illusory target disappearances would occur independently in the left and right hemifields. Both illusory and real target disappearance were followed by an alpha lateralization with weaker contralateral than ipsilateral alpha activity (~10 Hz). However, only the illusion showed early alpha lateralization in the opposite direction, which preceded the alpha effect present for both conditions and coincided with the estimated onset of the illusion. The duration of the illusory disappearance was further predicted by the magnitude of this early lateralization when considered over subjects. In the gamma band (60-80 Hz), we found an increase in activity contralateral relative to ipsilateral only after a real disappearance. Whereas early alpha activity was predictive of onset and length of the illusory percept, gamma activity showed no modulation in relation to the illusion. Our study demonstrates that the spontaneous changes in visual alpha activity have perceptual consequences.

Real color captures attention and overrides spatial cues in grapheme-color synesthetes but not in controls.

Grapheme-color synesthetes perceive color when reading letters or digits. We investigated oscillatory brain signals of synesthetes vs. controls using magnetoencephalography. Brain oscillations specifically in the alpha band (∼10Hz) have two interesting features: alpha has been linked to inhibitory processes and can act as a marker for attention. The possible role of reduced inhibition as an underlying cause of synesthesia, as well as the precise role of attention in synesthesia is widely discussed. To assess alpha power effects due to synesthesia, synesthetes as well as matched controls viewed synesthesia-inducing graphemes, colored control graphemes, and non-colored control graphemes while brain activity was recorded. Subjects had to report a color change at the end of each trial which allowed us to assess the strength of synesthesia in each synesthete. Since color (synesthetic or real) might allocate attention we also included an attentional cue in our paradigm which could direct covert attention. In controls the attentional cue always caused a lateralization of alpha power with a contralateral decrease and ipsilateral alpha increase over occipital sensors. In synesthetes, however, the influence of the cue was overruled by color: independent of the attentional cue, alpha power decreased contralateral to the color (synesthetic or real). This indicates that in synesthetes color guides attention. This was confirmed by reaction time effects due to color, i.e. faster RTs for the color side independent of the cue. Finally, the stronger the observed color dependent alpha lateralization, the stronger was the manifestation of synesthesia as measured by congruency effects of synesthetic colors on RTs. Behavioral and imaging results indicate that color induces a location-specific, automatic shift of attention towards color in synesthetes but not in controls. We hypothesize that this mechanism can facilitate coupling of grapheme and color during the development of synesthesia.

Top-down controlled alpha band activity in somatosensory areas determines behavioral performance in a discrimination task.

The brain receives a rich flow of information which must be processed according to behavioral relevance. How is the state of the sensory system adjusted to up- or downregulate processing according to anticipation? We used magnetoencephalography to investigate whether prestimulus alpha band activity (8-14 Hz) reflects allocation of attentional resources in the human somatosensory system. Subjects performed a tactile discrimination task where a visual cue directed attention to their right or left hand. The strength of attentional modulation was controlled by varying the reliability of the cue in three experimental blocks (100%, 75%, or 50% valid cueing). While somatosensory prestimulus alpha power lateralized strongly with a fully predictive cue (100%), lateralization was decreased with lower cue reliability (75%) and virtually absent if the cue had no predictive value at all (50%). Importantly, alpha lateralization influenced the subjects' behavioral performance positively: both accuracy and speed of response improved with the degree of alpha lateralization. This study demonstrates that prestimulus alpha lateralization in the somatosensory system behaves similarly to posterior alpha activity observed in visual attention tasks. Our findings extend the notion that alpha band activity is involved in shaping the functional architecture of the working brain by determining both the engagement and disengagement of specific regions: the degree of anticipation modulates the alpha activity in sensory regions in a graded manner. Thus, the alpha activity is under top-down control and seems to play an important role for setting the state of sensory regions to optimize processing.

Alpha oscillations correlate with the successful inhibition of unattended stimuli.

Because the human visual system is continually being bombarded with inputs, it is necessary to have effective mechanisms for filtering out irrelevant information. This is partly achieved by the allocation of attention, allowing the visual system to process relevant input while blocking out irrelevant input. What is the physiological substrate of attentional allocation? It has been proposed that alpha activity reflects functional inhibition. Here we asked if inhibition by alpha oscillations has behavioral consequences for suppressing the perception of unattended input. To this end, we investigated the influence of alpha activity on motion processing in two attentional conditions using magneto-encephalography. The visual stimuli used consisted of two random-dot kinematograms presented simultaneously to the left and right visual hemifields. Subjects were cued to covertly attend the left or right kinematogram. After 1.5 sec, a second cue tested whether subjects could report the direction of coherent motion in the attended (80%) or unattended hemifield (20%). Occipital alpha power was higher contralateral to the unattended side than to the attended side, thus suggesting inhibition of the unattended hemifield. Our key finding is that this alpha lateralization in the 20% invalidly cued trials did correlate with the perception of motion direction: Subjects with pronounced alpha lateralization were worse at detecting motion direction in the unattended hemifield. In contrast, lateralization did not correlate with visual discrimination in the attended visual hemifield. Our findings emphasize the suppressive nature of alpha oscillations and suggest that processing of inputs outside the field of attention is weakened by means of increased alpha activity.