Chapter 3.1 - Sensory Systems and Attention Modulation

Abstract

The brain regions where neurons respond to stimulation of a certain type of receptors are called sensory systems. There are different sensory modalities that give us sensations of images, sounds, and body movements. The information flow in the sensory systems is modulated by attention which is associated with enhancement of relevant sensory information and suppression of irrelevant sensory information. A canonical event related potential in both visual and auditory modalities includes P1 and N1 waves. In the visual modality the N1 is associated with discrimination operation. When stimuli are repeatedly presented in a particular order the brain forms the neuronal model of sensory stimulation so that when a new stimulus violates the model hypothetical “change” detectors are activated. In the visual modality activation of the change detectors is reflected in the visual mismatch negativity wave. Activation of a personal memory is attributed to the visual N170 wave which is partly generated in the fusiform gyrus. This area is also involved in generation of N250 wave which appears in response to stimulus repetition. When the stimulus is mismatched with the template in working memory the temporaly generated P2 (or P250) wave emerges. The P2 may appear together with N250 but also alone. Reactivity of the auditory cortex is assessed by the N1/P2-wave of the auditory ERP. The P1/N1 is modulated by the level of serotonin in the auditory cortex and modulated by the loudness of auditory stimulation. The loudness dependence of auditory evoked potentials is served as a marker for central serotonergic neurotransmission. The auditory mismatch negativity is elicited in response to rare deviant stimuli of oddball tasks. If the deviancy is large it produces orienting response which is reflected in the Novelty P3 wave. The operations of sensory processing can be separated by different methods of blind source separation approach.