Hitting an uncertain target

Abstract

Experiments in which monkeys have to select or estimate the location of a target are revealing more about the role of the dorsal premotor cortex in decision making.

Keywords: decision making; neuroscience; planning; reaching; rhesus macaque; single neurons.

Figure 1.. Target selection and target estimation.

(A) In a target selection situation there is a choice between two or more, clearly distinct, options. In this example there are two options (indicated by the two red arrows), and each option is associated with a specific probability of success (indicated by the numbers). A region of the brain called the dorsal premotor cortex plays an important role in making target selection decisions (also known as categorical decisions), while the primary motor cortex is responsible for executing the decision. (B) In a target estimation situation there is an infinite number of options (six of which are indicated by red arrows), and the probability of success can be plotted as a distribution with two peaks (yellow line). (C) Dekleva et al. have performed experiments on monkeys to explore the roles played by the dorsal premotor cortex and the primary motor cortex in making target estimation decisions (also known as continuous decisions). In the experiments the monkeys had to select a specific direction from a range of possible directions on the basis of incomplete visual information. Dekleva et al. measured how the level of neural activity (y-axis) in these two regions of the brain varied as a function of the angle (x-axis) between the preferred direction of the neurons and the chosen direction; they also varied the degree of uncertainty in the visual information provided to the monkeys about the location of the target. The range of possible directions was wide (orange arrows) when the uncertainty in the visual information provided to the monkeys was high, and the range was narrow (green arrows) when the uncertainty was low. In both regions the level of neural activity was highest when the angle between the preferred direction and the chosen direction (indicated by the vertical arrow) was zero. However, high levels of neural activity were observed over a relatively wide range of angles in the dorsal premotor cortex (left inset), and this range was higher when the degree of uncertainty was higher (orange line). In the primary motor cortex, on the other hand, high levels of neural activity were only observed for a narrow range of directions around the chosen direction, independent of the degree of uncertainty in the visual information (right inset).