Session 3 - Details

A neural population view on how the brain achieves both stable and rapidly adaptable behaviour

Juan Álvaro Gallego

The analysis of neural population activity in several brain cortices has consistently uncovered low-dimensional subspaces that capture a significant fraction of neural variability. These “neural manifolds” are spanned by specific patterns of correlated neural activity, whose activation are often called “latent dynamics”. I will discuss a model of brain function in which these latent dynamics, rather than the independent modulation of single neurons, drive behaviour.

Animals readily execute learnt behaviours in a consistent manner. How does the brain achieve this stable control? We recorded from neural populations in premotor, primary motor, and somatosensory cortices for up to two years as monkeys performed the same task. Remarkably, despite the unavoidable changes in recorded neurons, the population latent dynamics remain stable. Such stability allows reliable decoding of behavioural features for the entire timespan, while fixed decoders based on the recorded neural activity degrade substantially.

Perhaps the other most notable feature about animal behaviour is that we can adapt our movements very rapidly, even after a single error. When monkeys need to learn to counteract a velocity-dependent force field, the activity of single motor and premotor cortical neurons changes in complex ways; such changes puzzled neuroscientists for many years. I will show that adopting a “population view” reveals that despite these changes in single neuron activity, the neural manifold remains stable. Interestingly, motor adaptation is paralleled by the formation of new motor plans that are associated with novel latent dynamics. These observations indicate that rapid learning needs not be associated to fast synaptic changes.

A population view of how the brain works allows revealing both robust and rapidly changing patterns of neural activity that mediate behaviour. Given that neural manifolds are found throughout the brain, from prefrontal to visual cortex and even hippocampus, similar principles may apply to non-motor functions.

Neural dynamics underlying planning of sequences of actions in freely moving monkeys

Florentin Wörgötter, Alexander Gail, Christian Testzlaff, Michael Fauth

In daily life, actions are occurring as part of action sequences, like walking towards a door, opening it, switching on the light, etc. Humans usually plan ahead, mentally creating an action plan for a follow-up action or an action sequence, while still busy executing ongoing actions. If an action goal requires multiple steps for getting achieved, an agent usually knows the different individual actions already at the start of an action sequence. However, the neuronal characteristics of sequence planning and co-occurring execution and planning remains unclear up to now. To address this problem, we developed a new framework allowing the investigation of behavioral and neuronal dynamics of unrestrained monkeys performing different sequences of actions. Using this framework, we extracted and identified neuronal signatures of action planning from monkey’s neuronal activities in parietal and pre-motor brain areas. Our results show that the knowledge of a specific action to be executed is present already early during action sequence execution and over the time passed down along several brain areas, suggesting a hierarchy of action planning and execution. Decoding of planned action during ongoing action is an important prerequisite for smooth proactive control of neuroprosthetic devices or ambient assisted living (AAL) environments.

Computational Neuroscience Group