Neurobiologische Grundlagen der Aufmerksamkeit: „Über die Freiheit der Wahl”

Abstract

Introduction: Attention is viewed as the selective aspect of perception. This selective process is represented as a choice, often but not always constrained by the initial possibilities, motivation and adaptive aims. Fundamental among numerous useful divisions of the concept, is the differentiation of automatic and controlled attention that largely incur serial and parallel processing of information (a classification is proposed in figure 1). Neurophysiology: Selective attention to a stimulus implies that some information is passed on for further processing - this passage depends on the synchronous firing of the relevant neuronal pathways. The EEG sums these and a look at the average after an event shows excitatory and inhibitory components (event-related potentials, ERPs) that relate to the processing stages from registration, inhibiting interference from other processes and stimulus categorisation. Negativities (excitation) can be recorded for deviant detection (automatic, e.g. mismatch negativity, MMN) and attended traces (controlled processing, e.g. negative difference, Nd - see figure 2 for their maturation across adolescence). Gamma, beta and theta frequency bands in the EEG reflect differentially the binding of related features in nearer and further regions of function. Neurotransmitter Roles: The chemical coding of these neural systems with the biogenic amine transmitters allows for a division of labour in the mechanisms necessary for information. These are described in terms of volume control (serotonin), tuning (noradrenaline) and switching (dopamine). The effect of acetylcholine seems to reflect a mechanism by which a stimulus by means of its salience captures automatic processing. (The ascending sensory path, cortical feedback and the mesocorticolimbic source of modulation are schematically illustrated in figure 3) An Anatomy of Attention: Functional magnetic imaging (fMRI) of brain regions activated during attentional processing show that there are 'epicentres' of attentional function superimposed on variable diffusely distributed activity patterns (Mesulam, 1999). Frontal regions exert an executive role, facilitated by cingulate activity in conflict and error-control. Parietal loci on the left and right register temporal and spatial identification, respectively, of events whose relevance can be assessed by comparator mechanisms in the temporal lobe. (Figure 4, compares fMRI and PET activation [frontal, cingulate & intra-parietal sulcus] during an attentional task, Mesulam, 1999.) Choices of what is relevant - selective attention - for the adaptive organisation of response thus reflect a concerted effort within a network of heteromodal cortices based on the basic mechanisms for sorting information arising out of the brainstem.