The challenge of non-invasive cognitive physiology of the human brain: how to negotiate the irrelevant background noise without spoiling the recorded data through electronic averaging

Brain mechanisms involved in selective attention in humans can be studied by measures of regional blood flow and metabolism (by positron emission tomography) which help identify the various locations with enhanced activities over a period of time of seconds. The physiological measures provided by sc...

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Bibliographic Details
Published in:Philosophical transactions of the Royal Society of London. Series B. Biological sciences 1999-07, Vol.354 (1387), p.1295-1305
Main Authors: Tomberg, Claude, Desmedt, John E.
Format: Article
Language:English
Subjects:
Attention - physiology
Brain - blood supply
Brain - diagnostic imaging
Brain - physiology
Brain Imaging
Cerebrovascular Circulation
Cognition - physiology
Cognitive Unconscious
Data Interpretation, Statistical
Electric potential
Evoked Potentials
Fingers
Hands
Humans
Mental stimulation
Non-Averaged Brain Potentials
Perceptual Processing
Physical Stimulation
Physiological stimulation
Physiology
Physiology Of Cognition
Psychophysiology
Regional Blood Flow
Scalp
Selective Attention
Thumb
Tomography, Emission-Computed
Unconscious mind
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Summary:Brain mechanisms involved in selective attention in humans can be studied by measures of regional blood flow and metabolism (by positron emission tomography) which help identify the various locations with enhanced activities over a period of time of seconds. The physiological measures provided by scalp-recorded brain electrical potentials have a better resolution (milliseconds) and can reveal the actual sequences of distinct neural events and their precise timing. We studied selective attention to sensory inputs from fingers because the brain somatic representations are deployed over the brain convexity under the scalp thereby making it possible to assess distinct stages of cortical processing and representation through their characteristic scalp topographies. In the electrical response to a finger input attended by the subject, the well-known P300 manifests a widespread inhibitory mechanism which is released after a target stimulus has been identified. P300 is preceded by distinct cognitive electrogeneses such as P40, P100 and N140 which can be differentiated from the control (obligatory) profile by superimposition or electronic subtraction. The first cortical response N20 is stable across conditions, suggesting that the first afferent thalamocortical volley is not affected by selective attention. At the next stage of modality-specific cortex in which the sensory features are processed and represented, responses were enhanced (cognitive P40) only a very few milliseconds after arrival of the afferent volley at the cortex, thus documenting a remarkable precocity of attention gain control in the somatic modality. The physiology of selective attention also provides useful cues in relation to non-target inputs which the subject must differentiate in order to perform the task. When having to tell fingers apart, the brain strategy for non-target fingers is not to inhibit or filter them out, but rather to submit their input to several processing operations that are actually enhanced when the discrimination from targets becomes more difficult. While resolving a number of such issues, averaged data cannot disclose the flexibility of brain mechanisms nor the detailed features of cognitive electrogeneses because response variations along time have been ironed out by the bulk treatment. We attempted to address the remarkable versatility of humans in dealing with their sensory environment under ecological conditions by studying single non-averaged responses. We identif
ISSN:0962-8436
1471-2970
DOI:10.1098/rstb.1999.0480