The mammalian brain is assembled from local neural circuits that are connected into networks, in which signals are encoded as brief voltage ‘spikes’. This spiking activity is used to communicate information between neurons, and is the basis of the computations performed in the brain. Spiking rates in different neurons, and their change over time, are thought to encode diverse features such as the properties of sensory stimuli, the location of an important object in the environment, movements to be made, or memories of events. Ultimately, our ability to attend to particular aspects of the world, to predict events, and to make decisions results from activity in neuronal circuits, but our understanding of how these circuits are organised, and how they are formed into large-scale networks, remains rudimentary.
From studies in the last 50 years we understand the initial processing of sensory stimuli. Moreover, physiological studies in animals and human imaging studies have revealed the brain regions that are involved in simple behavioural tasks, while anatomical tracing has shown the broad principles of how brain areas are connected. However, the functional nature of connections – i.e., how they determine activity and behaviour – remains poorly understood, as is the encoding of information. These data are essential to develop specific models of brain function. Thus, a central theme of the Centre is to understand neural circuits, and to determine how their functions are encoded in neural networks.
Neural Circuits – behavioural tasks
The Neural Circuits research theme uses behavioural tasks that are well established and for which the brain regions involved are well understood. For example, simple stimulus-response (Pavlovian conditioning) behavioural experiments can be employed in the contexts of attention, prediction, and decision. To study activity in the underlying neural circuits we record from multiple brain sites in awake behaving animals. These recordings lead to a model of how different brain centres drive the relevant behaviour.
Neural Circuits – optogenetic modulation
The new method of optogenetic modulation allows activation or silencing of neurons with millisecond precision, and can be engaged to activate the source (cell bodies) or destination (cell terminals) of functional paths. The anatomy and physiology of these connections can then be determined. These studies provide information on the activity of neural networks in rodents and non-human primates. A key part of our Centre research strategy is to test the relevance of these networks to human brain function, by implementing analogous behavioural tasks in non-invasive imaging studies.