Brain Stimulation in the Study of Neuronal Functions for Conscious Sensory Experiences

  • B. Libet
Part of the Contemporary Neuroscientists book series (CN)


Some features of cerebral neuronal functions that are uniquely related to generation of conscious sensory responses, have been discovered. Included are two temporal factors: (1) Substantial delays, of up to about 0.5 sec, before achieving cerebral “ neuronal adequacy“ appear to be required for eliciting a sensory experience. This includes the demonstration that a cortical stimulus (C) can retroactively modify a skin (S)-induced sensation even when C stimulus begins up to 500 msec after S stimulus. (2) However, there appears to be a subjective referral of the experience back to the time of the cortical primary evoked response to S; subjectively the skin sensation would thus appear to have no delay. Stimuli that are inadequate for eliciting conscious sensory experience can nevertheless evoke considerable neuronal activity, including that represented in direct cortical responses or in primary (early) components of evoked potentials. Virtually all the qualities of somatic sensation (except pain) can be elicited by stimuli at postcentral gyrus, when intensities of suitable trains of pulses are kept down to liminal levels. Some additional implications, for the manner in which mental and neural events are related, are discussed.

Key words

Electrical stimulation Human brain Somatosensory cortex Somatosensory qualities Conscious sensory experience Subjective referral of sensations 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Desmedt JE, Robertson D (1977) Differential enhancement of early and late components of the cerebral somatosensory evoked potentials during forced-paced cognitive tasks in man. J Physiol (Lond) 271:761–782Google Scholar
  2. Doty RW (1969) Electrical stimulation of the brain in behavioral cortex. Ann Rev Physiol 20:289–320CrossRefGoogle Scholar
  3. Eccles JC (1980) The Human Psyche. Springer, Berlin Heidelberg New York, 279 pagesCrossRefGoogle Scholar
  4. Fehrer E, Raab O (1962) A comparison of reaction time and verbal report in the detection of masked stimuli. J Exp Psychol 64:126–130PubMedCrossRefGoogle Scholar
  5. Jasper HH (1963) Studies of non-specific effects upon electrical responses in sensory system. In: Moruzzi G, Albe-Fessard D, Jasper HH (eds) Progress in brain research, Vol. I Elsevier, Amsterdam, pp 272–293CrossRefGoogle Scholar
  6. Libet B (1965) Cortical activation in conscious and unconscious experience. Perspect Biol Med 9:77–86PubMedGoogle Scholar
  7. Libet B (1966) Brain stimulation and the threshold of conscious experience. In: Eccles JC (ed) Brain and conscious experience. Springer-Verlag, Berlin Heidelberg New York, pp 165–181Google Scholar
  8. Libet B (1973) Electrical stimulation of cortex in human subjects and conscious sensory aspects. In: Handbook of sensory physiology, vol. II, pp 743–790) Iggo A (ed). Springer, Berlin Heidelberg New YorkGoogle Scholar
  9. Libet B (1978) Neuronal vs. subjective timing, for a conscious sensory experience. In: Buser PA, Rougeul-Buser A (eds) Cerebral Correlates of Conscious Experience. Elsevier/North Holland Biomedial Press, Amsterdam, pp 69–82Google Scholar
  10. Libet B (1981a) ERPs and conscious awareness. In:Galambos R, Hill-yard SA (eds) Electrophysiological Approaches to Human Cognitive Processing. (Neurosci Res Program Bull 20:171-175). The MIT Press Journals, CambridgeGoogle Scholar
  11. Libet B (1981b) The experimental evidence for subjective referral of sensory experience backwards in time. Philos of Sci 48:182–197CrossRefGoogle Scholar
  12. Libet B, Alberts WW, Wright EW, Delattre LD, Levin G, Feinstein B (1964) Production of threshold levels of conscious sensation by electrical stimulation of human somatosensory cortex. J Neuro-physiol 27:546–578Google Scholar
  13. Libet B, Alberts WW, Wright EW, Feinstein B (1967) Responses of human somatosensory cortex to stimuli below threshold for conscious sensation. Science 158:1597–1600PubMedCrossRefGoogle Scholar
  14. Libet B, Alberts WW, Wright EW, Feinstein B (1972) Cortical and thalamic activation in conscious sensory experience. In:Somjen GG (ed) Neurophysiology studied in man. Excerpta Medica, Amsterdam, pp 157–168Google Scholar
  15. Libet B, Alberts WW, Wright EW, Lewis M, Feinstein B (1975) Cortical representation of evoked potentials relative to conscious sensory responses and of somatosensory qualities in man. In:Kornhuber HH (ed) The somatosensory system. Thieme, Stuttgart, pp 291–308Google Scholar
  16. Libet B, Wright EW Jr, Feinstein B, Pearl DK (1979) Subjective referral of the timing for a conscious sensory experience: a functional role for the somatosensory specific projection system in man. Brain 102:191–222CrossRefGoogle Scholar
  17. Mountcastle VB (1967) The problem of sensing and the neural coding of sensory events. In:Quarton GC, Melnechuk T, Schmitt FO (eds) The neurosciences. Rockefeller University Press, New York, pp 393–408Google Scholar
  18. Nashold B, Somjen G, Friedman H (1972) Paresthesias and EEG potentials evoked by stimulation of the dorsal funiculi in man. Exp Neurol 36:273–287PubMedCrossRefGoogle Scholar
  19. Penfield W (1958) The Excitable Cortex in Conscious Man. Liverpool University Press, Liverpool, 42 ppGoogle Scholar
  20. Penfield W (1959) The interpretive cortex. Science 129:1719–1725PubMedCrossRefGoogle Scholar
  21. Popper KR, Eccles JC (1977) The self and its brain. Springer, Berlin Heidelberg New York, 597 ppCrossRefGoogle Scholar
  22. Sherrington CS (1951) Man on his Nature. Cambridge University Press, London, 300 pages (2nd edition)Google Scholar
  23. Shevrin H, Dickman S (1980) The psychological unconscious: a necessary assumption for all psychological theory? Am Psychol 35:421–434CrossRefGoogle Scholar
  24. Shevrin H, Smith WH, Fritzler D (1971) Average evoked responses and verbal correlates of unconscious mental processes. Psychophysiology 8:149–162PubMedCrossRefGoogle Scholar
  25. Sperry RW (1980) Mind-brain interaction: mentalism, yes; dualism, no. Neuroscience 5:195–206PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1993

Authors and Affiliations

  • B. Libet
    • 1
  1. 1.Neurological Institute-Department of Neuroscience, Mt. Zion Hospital, and Department of PhysiologyUniversity of CaliforniaSan FranciscoUSA

Personalised recommendations