How the brain learns
The basal forebrain (a group of structures near the bottom-front of the brain) is apparently pivotal to cognitive functions like attention and learning. Scientists do not fully understand, however, how it performs these tasks. This is largely due to problems with identifying which signals come from each different cell type found in this area of the brain. To solve this problem, the EU-funded NBATTENTION (The role of the basal forebrain in attention and learning) initiative developed a way to identify and record signals from distinct neurons in the basal forebrain. They adapted ground breaking techniques to study which neurons mice use when given cognitive tasks. Neurons perform different roles by releasing various types of chemical messenger called neurotransmitters. These can excite (stimulate) the brain, inhibit (calm or dampen) the brain, or modulate the way other brain structures process information. NBATTENTION used a revolutionary light-activated technique called optogenetic tagging to manipulate and record signals from individual neurons in the basal forebrains of normally behaving mice. In particular, they recorded how different neurons responded when mice were set tasks requiring attention and learning. They found that the modulatory neurons fired rapidly in response to reward and punishment, especially when both triggers were unexpected. Since the responses correlated with the degree of unexpectedness, these neurons may be responsible for surprise-based reinforcement learning. This is an important survival mechanism that allows a subject to either repeat or avoid a behaviour based on a prior, unpredictable, experience. In contrast, the inhibitory neurons responded to reward- and punishment-predictive stimuli with a more sustained firing rate. These results suggest that basal forebrain modulatory neurons control learning by rapidly activating the cortex after behavioural feedback. They do not, however, support the idea that the modulatory nervous system is involved in behaviours requiring sustained attention, like remaining vigilant and focused. Since the basal forebrain's modulatory neurons are implicated in cognitive diseases like Alzheimer's and Parkinson's, NBATTENTION's results could greatly improve their diagnosis and treatment.
Keywords
Sustained attention, learning, neurons, basal forebrain, NBATTENTION, cognitive diseases
