Historically, brain science has focused on how distinct brain regions carry out specialised functions such as sensation, motor control and cognition. This approach has led to a ‘compartmentalised’ map of thebrain, whereby nerve cells (neurons) with shared morphology and function, located in the same area, correspond to discrete information processing modules. However, it is now recognised that the real challenge is to understand how activity is coordinated across brain areas, in real time. Such coordination is crucial for virtually all brain functions.
For example, when you cross the street, the sight and sound of an oncoming car are coordinated to yield a coherent, multi-sensory perception. Brain centres for movement planning are coordinated with the ones that produce goal-directed actions (initiating movements to ensure safe crossing). At the same time, sensory feedback from the environment is used to refine ongoing movement. These principles also apply to high-level functions such as language, where activity in many areas is coordinated to extract meaning and generate speech. In sum, the brain needs to be understood in terms of the interaction of its parts, not by considering each part in isolation.
Recent developments in brain imaging and brain stimulation allow, more than ever, functional study of the living human brain. Despite this advance, there are still only tenuous connections between the results of human studies and those of experimental studies in other mammals, which can provide the most detailed information about the cellular processes and neural circuits of the brain.
The Brain Systems research theme addresses this problem by conducting parallel investigations in rodents, monkeys and humans. A key strategy is to develop measures of simple behaviours (e.g. shifting of visual attention, prediction of movement trajectories, and perceptual decisions on discrete sensory events). In humans, these tasks are performed in brain imaging and stimulation experiments; in rodents and nonhuman primates, they are done during electrode-array recordings from brain cells.
Brain Systems – imaging
In humans, combining brain stimulation and imaging allows us to target specific brain areas and trace their system-wide influence on neural activity. For example, we can stimulate primary sensory areas and measure propagation of neural activity to other areas while the brain is at ‘rest’ and during action. In other experiments we are stimulating high-level ‘executive’ areas critical for integrative functions, and trace the effects on lower level sensory and motor areas. In rodents and monkeys parallel investigations are being undertaken by micro-stimulation of local circuits via implanted electrodes and by using the new method of optogenetic modulation, in which light sensitive molecules are incorporated into brain cells, allowing neural activation by laser stimulation. Concurrent recordings or neuronal activity are being made via electrode arrays implanted in both sensory and executive cortical areas, allowing us to examine how activity in networks of neurons underlies integrative functions.
Brain Systems – analytic measures
The Brain Systems research theme takes advantage of new analytic measures of human brain function, and apply these to non-human mammalian brains. For example, the traditional approach to analysis of brain imaging data is to subtract activity in control conditions from activity associated with a task. This approach however biases outcomes toward localised function in specialised areas. To address this challenge, our investigators adopt and further develop analysis methods that can point to the physiological interactions within brain networks that underlie integrative functions. We use new ‘decoding’ techniques to reveal patterns of network activity that are invisible to conventional analyses. Most importantly, we apply these methods to recordings from connected nerve cell groups and MRI experiments in animals, revealing how the network components are built up at a local (neuronal circuit) level.