Animals must react quickly to objects and events in the environment to survive, especially when their decisions could result in a reward or punishment. Based on this fact, scientists have assumed that the speed of decision-making during behavioral tasks is affected by motivational salience—the extent to which an object or event predicts important behavioral outcomes. Neurons in a brain region called the basal forebrain (BF) respond to motivationally salient stimuli, but the influence of these BF neurons on decision-making speed has been unclear.
In a study published this month in PLOS Biology, Irene Avila and Shih-Chieh Lin of the National Institute on Aging at the National Institutes of Health provide new insights into how motivational salience not only speeds up reaction times but also reduces variability in decision-making speed. Avila and Lin's findings suggest that the activity of BF neurons determines the speed of rats' decisions in response to motivationally salient stimuli, providing a possible neural explanation for the slower decision-making speeds seen in conditions ranging from depression to dementia.
To examine the relationship between motivational salience and decision-making speed, Avila and Lin trained rats to stick their nose through a port in a Plexiglas chamber and wait for a noise that signaled a reward. White noise indicated that the rats would receive a large reward of four drops of water, whereas a clicking sound signaled a small reward of only one drop of water. During some trials, no noise or reward was presented.