New research has revealed how three important brain signaling
chemicals affect the way that we handle uncertainty. It turns out that
noradrenaline regulates our estimates of how unstable the environment
is, acetylcholine helps us adapt to changing environments, and dopamine
pushes us to act on our beliefs about uncertainty. The research,
publishing 15 November in the open-access journal PLOS Biology, was led by Louise Marshall and Dr Sven Bestmann at the UCL (University College London) Institute of Neurology.
The study involved 128 healthy participants who took part in a reaction-time task designed to test how they handled uncertainty.
Participants were all given either a placebo or a drug to block
noradrenaline, acetylcholine or dopamine before starting the task.
Participants responded to symbols that were presented one after the
other by pressing a corresponding button. The probability of each symbol
appearing was dependent on the symbol that appeared previously; for
example, if a participant had just seen symbol A, there was an 85%
chance that symbol B would appear next. Every 50 trials, these
probability patterns changed without warning, so participants had to
detect these new patterns and adjust their responses accordingly.
Lead author Louise Marshall said: “Interacting with our dynamic and
ever-changing environment requires us to frequently update our beliefs
about the world. By learning the relationships that link events
occurring in our environment, we can predict future events, and execute
fast, accurate responses. However, the environment’s complex dynamics
give rise to uncertainty about the relationships between events, and
uncertainty about the stability of these relationships over time.
Several brain chemicals have been proposed to modulate how we handle
uncertainty. Here we combined pharmacological interventions and novel
computational models to determine how noradrenaline, acetylcholine and
dopamine enable our brains to learn the changing relationships in our
environment. The results shed important light on how humans learn to
behave under uncertainty.”
Abstract
Pharmacological Fingerprints of Contextual Uncertainty
Successful interaction with the environment requires flexible
updating of our beliefs about the world.
By estimating the likelihood of
future events, it is possible to prepare appropriate actions in advance
and execute fast, accurate motor responses. According to theoretical
proposals, agents track the variability arising from changing
environments by computing various forms of uncertainty. Several
neuromodulators have been linked to uncertainty signalling, but
comprehensive empirical characterisation of their relative contributions
to perceptual belief updating, and to the selection of motor responses,
is lacking. Here we assess the roles of noradrenaline, acetylcholine,
and dopamine within a single, unified computational framework of
uncertainty. Using pharmacological interventions in a sample of 128
healthy human volunteers and a hierarchical Bayesian learning model, we
characterise the influences of noradrenergic, cholinergic, and
dopaminergic receptor antagonism on individual computations of
uncertainty during a probabilistic serial reaction time task. We propose
that noradrenaline influences learning of uncertain events arising from
unexpected changes in the environment. In contrast, acetylcholine
balances attribution of uncertainty to chance fluctuations within an
environmental context, defined by a stable set of probabilistic
associations, or to gross environmental violations following a
contextual switch. Dopamine supports the use of uncertainty
representations to engender fast, adaptive responses.
I am a professional ICT personnel, Chief System Analyst, blogger, Managing Director/Chief Executive Officer at Gatmond Internationals inc. and Country Director at Wake Up For Your Right Internationals USA (Nigeria Branch).
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