Once rhesus monkeys learn to associate a picture with a reward, the reward by itself becomes enough to alter the activity in the monkeys' visual cortex. This finding was made by neurophysiologists Wim Vanduffel and John Arsenault (KU Leuven and Harvard Medical School) and American colleagues using functional brain scans and was published recently in the leading journal Neuron.
Our visual perception is not determined solely by retinal activity. Other factors also influence the processing of visual signals in the brain. "Selective attention is one such factor," says Professor Wim Vanduffel. "The more attention you pay to a stimulus, the better your visual perception is and the more effective your visual cortex is at processing that stimulus. Another factor is the reward value of a stimulus: when a visual signal becomes associated with a reward, it affects our processing of that visual signal. In this study, we wanted to investigate how a reward influences activity in the visual cortex."
To do this, the researchers used a variant of Pavlov's well-known conditioning experiment: "Think of Pavlov giving a dog a treat after ringing a bell. The bell is the stimulus and the food is the reward. Eventually the dogs learned to associate the bell with the food and salivated at the sound of the bell alone. Essentially, Pavlov removed the reward but kept the stimulus. In this study, we removed the stimulus but kept the reward."
In the study, the rhesus monkeys first encountered images projected on a screen followed by a juice reward (classical conditioning). Later, the monkeys received juice rewards while viewing a blank screen. fMRI brain scans taken during this experiment showed that the visual cortex of the monkeys was activated by being rewarded in the absence of any image.
Importantly, these activations were not spread throughout the whole visual system but were instead confined to the specific brain regions responsible for pr
|Contact: Wim Vanduffel|