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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - BBRhythms (Brain and body rhythms: on the relationship between movement and percept)

Teaser

Summary

In the awake state, our body is constantly in motion and we meet most perceptual challenges while moving. Nevertheless, up to now, the vast majority of studies that investigated perceptual mechanisms and specifically sensory brain responses related to perception were conducted under strict movement suppression. Exciting findings from animal electrophysiological research in the past years however show that an increased rate of body movements results in an enhanced response of neurons within the visual system. This suggests, that perceptual processes are influenced by body movements already at a basic level of sensory processing.
The main aim of the proposed research is to decode the relationship between body movements and perception in humans. This research could uncover mechanisms of how perceptual processes are modulated by movements and possibly optimized for certain movement sates. The proof of such mechanisms would constitute a ground-breaking step in understanding perception during natural behavior and could further lead to a better understanding of perceptual changes during pathological movements as observed in many neurodegenerative diseases. Importantly, this research can also help evaluating to what extent the numerous work on perception in motionless subjects generalizes to natural behavior.

Work performed

With the use of our newly established functional mobile recording lab, we measured electrophysiology, eye movements, walking pattern and perception in freely moving humans.
Comparing brain activity during walking in light vs. darkness, we could show that walking is associated with a decrease in alpha activity over occipital cortex, even when visual input is not available during walking. Alpha activity (~10Hz) picked up over the occipital area has been considered a valuable marker of inhibitory processes and shown to coincide with an increase in neuronal firing. Therefore, our first study presents neurophysiological evidence in humans that walking leads to a downregulation in early visual neuronal activity, corroborating animal findings.
In our second study, we assessed brain activity probed in early visual areas and its perceptual consequences during walking. Extending the animal work, our results show complementary neurophysiological and behavioural evidence that neuronal modulation due to walking is indeed linked to specific perceptual changes. Our study further indicates that walking leads to a specific increase in the processing of peripheral visual input. Overall, our study shows that strategies of sensory information processing can differ between movement states.

In our second line of work, we started to investigate the relationship between different types of movements. It is often overlooked that if certain movements are suppressed others emerge or change its amplitude. All types of movements have however a specific influence on the perceptual outcome. This leads to the possibility of a complex and continuous influence of movements on perception.
We find that different eye related movements (pupil size, blinks and saccades) are differentially modulated by walking speed, dependent on the existence of visual input, and that blinks and saccades have a preferred phase of walking during which they occur. Further, not only walking but also talking influences eye related movements. Corroborating earlier results that the blink rate is increased during a conversation, we could ascribe this increase mainly to an interaction between facial muscles underlying lip movements and blinking. Analyzing the occurrence of fixational saccades during the execution of smooth pursuit eye movements further suggests shared neuronal processes during fixation and pursuit. Our work on eye related movements, walking and talking gives evidence that motor systems are tightly linked. Indeed, additional results suggest that microsaccades, saccades and blinks follow the same temporal sequence. This adds to the idea that there is an internal rhythm to which different motor outputs can log onto. Further investigating blink events using a bistable visual perceptual stimulus, we could show that the event of blinking influences the perceptual outcome qualitatively.

Our current findings clearly support our hypothesis that walking modulates visual cortical activity as well as eye related movements, thereby changing the perceptual outcome during movement as compared to standing still.

Final results

The investigation of walking induced modulation of perception and percept related neuronal activity was highly successful and faster than expected. However, due to the very reassuring results concerning our hypothesis, we are conducting additional experiments to gather a more thorough understanding of the specific influences of walking on perceptual mechanisms.
Concerning the work on the role of eye related movements, we hope to add conclusive results as to the influence of eye movements not only on behavior but also on brain activity. To this end 2 MEG studies, as well as the analysis of invasively recorded hippocampal data in the human brain and non-human data recorded from visual areas will be completed.