Every kid knows that moms have "eyes in the back of their heads."
Indeed, human beings are adept at fixing their gaze on one object while independently directing attention to others.
Salk Institute neurobiologists are beginning to tease apart the complex brain networks that enable humans and other higher mammals to achieve this feat.
In a study published in last week's issue of Neuron, the researchers report two classes of brain cells with distinct roles in visual attention, and highlight at least two mechanisms by which these cells mediate attention.
In the experiments, animals learned how to play a sophisticated video game that challenged their visual attention-focusing skills. During the game, Salk researchers recorded electrical activity from individual neurons in part of the visual cortex that has been implicated in mediating visual attention.
As illustrated in the demonstration, the neurons respond when a stimulus appears within a window (indicated by the circle) covering a small part of the visual field that the eye sees. Whenever the stimuli entered the neuron's receptive field, the cell produced a volley of electrical spikes, indicated by vertical tick marks.
Researchers found that neurons typically responded more strongly when attention was directed to the stimulus in their receptive fields. Upon closer inspection, however, the researchers noticed that different neurons produced differently shaped electrical spikes: "broad spikes" and "narrow spikes."
After sorting the neurons by waveform, the researchers observed that attention had different effects on the two different types of neurons.