Receptive Fields and the Specificity of Neuronal Firing

Neuronal firing does not occur at random. In the sensory parts of the brain, firing is triggered by properties of various input stimuli, such as the visual direction of a light stimulus, the pitch of a tone, or the spot of skin hit by some object. Outside the sensory areas of the brain, specificities for more abstract concepts have been found including cells representing place (the animal’s current position) or the numerosity of objects. In the motor parts of the brain, neurons have been found that fire preferably prior to movements of body parts into a certain direction. In the sensory pathways, the specificity of a neuron is quantified by means of its receptive field. Receptive fields are measured by correlating the activity of the neuron with externally recorded parameters of the stimulus; the approach is known as reverse correlationReverse correlation. In this chapter, we discuss the basic theory of visual receptive fields that can be extended to similar concepts in other sensory, motor, or associative areas. The theory is closely related to linear systems theory applied to spatiotemporal signals such as image sequences. Mathematically, it rests on integral equations of the convolution type which will be introduced in due course.