Does the brain speed up when we move?

The brain is traditionally divided into sensory and motor parts. The sensory parts - concerned with sight, hearing, or touch - inform an animal about the outside world. The motor parts control the muscles, and allow the animal to move through that world. Surprisingly, however, it is now clear that activity in sensory parts of the brain can also be influenced by self-movement. The purpose of these changes in sensory activity is not known. In this proposal we will test the hypothesis that these changes allow better and faster processing of sensory signals during self-movement.

Self-movement changes the patterns of sensory inputs provided to the brain compared to when sitting still. For example, crossing the road induces large and frequent changes in the patterns of light hitting the eye. During self-movement, therefore, the brain must contend with an increased rate of change in sensory signals. How sensory pathways are able to adapt to this increased rate is unknown, and is the focus of our research proposal.

We will answer this question by measuring visual responses in the visual pathway of the brain. We will use rodents (mice) as a model system, where the required experimental techniques are well-established. We will measure visual responses while the animal is still, and while it is engaging in self-movement. We will characterise the amplitude and dynamics of brain activity, at the level of single nerve cells, at the level of local brain circuits, and at the level of brain systems. Exploiting recent advances in experimental and computational techniques, which we have helped pioneer, we will measure activity in the output of the eye, the two major targets of the eye, and major areas in the cerebral cortex that process visual signals. Our measurements will therefore show how self-movement changes the speed at which nerve cells react to visual input, how it changes the communication between visual brain areas, and how these neural changes help an animal to see rapidly changing visual scenes.

This proposal is important because modern lifestyles are associated with decreased physical activity and increased sedentary behaviour. Active lifestyles are known to improve normal ageing, and have a positive impact on brain function and mental health, including increased attentional capacity and lower incidence of depression. Most previous research has focused on how physical activity leads to changes in the structure of the brain, and it is not known if self-movement also benefits brain function. As well as shedding light on the purpose of movement-related activity in sensory pathways, the proposed work may also help the general understanding of how and why physical activity influences brain function, and contributes to lifelong health. It may also guide the development of new approaches to improving function, or improving therapy, for people with visual disorders.

The aim of this project is to determine how self-movement influences the signals provided by sensory pathways through the brain. While it is now clear that, across modalities and species, sensory brain activity changes during self-movement, the purpose of these changes in activity is not known.

Our overall hypothesis is that the speed of visual processing increases during self-movement, allowing improved analysis of fast sensory signals.

The specific hypotheses we will test are:
1. Self-movement speeds up the processing of incoming sensory signals
2. Self-movement speeds up feedback signals in visual pathways
3. Self-movement improves the ability to respond to rapid sensory events

We will test these hypotheses by making measurements from the mouse visual system. We will record neural activity while mice are passively viewing visual stimuli and while they are performing a visual speed discrimination task we have developed for this purpose.

We will measure perceptual performance and record neural activity when the mouse is standing still and when it is running. To record from 100s of neurons in multiple brain areas simultaneously, we will use high-density electrophysiological probes (Neuropixels 2.0) targeted to the visual thalamus, mid-brain superior colliculus, primary visual cortex, and anterio-medial and posterio-medial higher visual areas. We will use two-photon imaging of retinal ganglion cell axon terminals to capture the influence of self-movement on the earliest stages of visual processing. We will assess the effects of movement on the temporal response dynamics of individual neurons in each area, on populations of neurons within and across different areas, and on perceptual performance.