Modulation of Neuronal Signalling

The unique feature that distinguishes this volume from a number of others addressing neural basis of visual perception and visual attention is that it contains a set of advanced-tutorial chapters that deal with neural modulatory mechanisms at multiple levels of the brain organization in the context of active vision. These chapters encompass modulatory mechanisms starting with the modulation at the level of single neurons (e.g. the level of synaptic transmission), through the level of neuronal ensembles (e.g. population codes), and ending with the modulations due to the behavioral states. The first section begins with the modulatory arousal mechanisms of the midbrain and the basal forebrain that influence the character of neuronal responses to visual stimuli in both cortex and thalamus. Even short-lived transient changes in the state of arousal are shown to affect the coding of visual information. The second section focuses on the contextual mechanisms that determine integration of visual information in the visual cortex based on the prior knowledge about the structure of the environment and the attention/intention mechanisms that endow representations of visual information with behavioural relevance. Selective attention is shown to determine the extent of contextual influences on perception and neuronal responses in the visual cortex. Cortico-cortical feedback connections are proposed to be critical in supporting this modulation of contextual influences. The third section explores neuronal codes that satisfy informational and temporal constraints set by rapidly unfolding behaviors associated with active vision. Finally, the fourth section is dedicated to the issues of correlating measures of perception and behaviour with underlying neuronal responses.