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The World of Touch – From Evoked Potentials to Conscious Perception

Published online by Cambridge University Press:  05 August 2019

Alan J. McComas
Alan J. McComas*
Affiliation:
Department of Medicine (Division of Neurology), McMaster University, Hamilton
*
McMaster University Health Sciences Centre, Department of Medicine (Division of Neurology), 1200 Main Street West, Hamilton, Ontario, Canada L8N 3Z5
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Abstract:

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Microelectrode recordings have enabled several maps of the body surface to be recognized in the mammalian somatosensory cortex. The maps appear to represent increasingly complex levels of analysis of the sensory message. At present the prevailing opinion is that the different components of the ERPs (event related potentials) represent sequential steps in such an analysis, and such an interpretation is supported by the enhancement of the ERPs when attention is paid to a somatic stimulus. However, there are a number of critical observations which are inconsistent with this view and suggest that the ERP enhancement may be an epiphenomenon. An alternative explanation for the ERPs is that they reflect discharges from the non-specific thalamic nuclei, and are essentially similar to the long latency responses which can be recorded from the cortex during sleep or anaesthesia. Lastly, a hypothesis is proposed for the neuronal events in the somatosensory cortex which culminate in a conscious perception. In this “RULER” model, the deep pyramidal neurones read out the sensory information which has been retained in the apical dendrites of more superficial cells, and do so at the end of successive “time-chunks”.

Résumé:

Résumé:

Les enregistrements par microélectrodes ont permis d'établir plusieurs cartes de la surface du corps dans le cortex somesthésique de mammifères. Ces cartes semblent représenter des niveaux de plus en plus complexes d'analyse des messages sensitifs. Actuellement, l'opinion courante est que les différentes composantes des potentiels liés aux événements (PREs) représentent des étapes séquentielles dans cette analyse et cette interprétation est supportée par le rehaussement des PREs quand on considère le stimulus somatique. Cependant, il existe un certain nombre d'observations critiques qui sont incompatibles avec cette interprétation et qui suggèrent que le rehaussement des PREs pourrait être un épiphénomène. Une autre explication des PREs est qu'ils reflètent des décharges de noyaux thalamiques non spécifiques et sont essentiellement semblables aux réponses à longue latence qui peuvent être enregistrées dans le cortex pendant le sommeil ou l'anesthésie. Finalement, nous proposons une hypothèse expliquant les événements neuronaux dans le cortex somesthésique dont le point culminant est la perception consciente. Dans le modèle “RULER”, les neurones pyramidaux profonds lisent l'information sensitive qui a été retenue dans les dendrites apicaux de cellules plus superficielles et le font à la fin de “portions de temps” successives.

Type
Review Article
Information
Canadian Journal of Neurological Sciences , Volume 26 , Issue 1 , February 1999 , pp. 7 - 17
Copyright
Copyright © The Canadian Journal of Neurological 1999

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