Perception and Consciousness


Fast, gamma rhythms range from 30 to 100 Hz, and may vary in frequency during a response. The 20-100 Hz range we consider here overlaps the beta band (15 to 30 Hz), but we will ignore the finer points of EEG classification here. The natural history and functional roles of synchronous gamma oscillations have been reviewed recently [5,10,12,22]. Below is a potted history.

Gamma rhythms occur in humans and other mammals following sensory stimuli. They often occur in brief runs in these responses. "Induced rhythms" at 50-60 Hz were first described in olfactory bulb by Adrian [1]. They have since been found in: olfactory [4], visual [3a,3b,6-8,11,22], auditory [13,16], somatosensory [2] and motor cortex [17,19,21]. Gamma oscillations also occur in the hippocampus [3,24], where the link with external sensory stimuli is less direct, but may still exist in the multimodal inputs it receives from higher order sensory cortices. Hippocampal gamma tends to occur during the theta (4-12 Hz) EEG that is a prominent feature of the hippocampus in vivo [3,23], especially during exploration.

In Man the auditory response includes brief "40 Hz transient responses" [18,25], which increase when the subject pays attention and which disappear with loss of consciousness during anaesthesia [14]. Repetitive auditory stimulation at ~40 Hz generates a large "40 Hz steady state response" [9]. MEG recordings in Man suggest that gamma rhythms can be very widespread [20], both during waking and dream states. Other MEG measurements in Man suggest that gamma rhythms may be organised to sweep across the whole brain, perhaps providing "temporal binding .... into a single cognitive experience" [15].


1 Adrian, E.D. The electrical activity of the mammalian olfactory bulb, Electroencephalogr. Clin. Neurophysiol. 2 (1950) 377-388.

2 Bouyer, J.J., Montaron, M.F., Vahnee, J.M., Albert, M.P. and Rougeul, A. Anatomical localization of cortical beta rhythms in cat, Neuroscience, 22 (1987) 863-869.

3 Bragin, A., Jand , G., N dasdy, Z., Hetke, J., Wise, K. and Buzs ki, G. Gamma (40-100 Hz) oscillation in the hippocampus of the behaving rat, J. Neurosci. 15 (1995) 47-60.

3a Eckhorn, R., Bauer, R., Jordan, W., Brosch, M., Kruse, W., Munk, M. and Reitboeck, H.J. Coherent oscillations: a mechanism of feature linking in the visual cortex? Multiple electrode and correlation analyses in the cat, Biol. Cybern. 60 (1988) 121-130.

3b Eckhorn, R., Reitboeck, H.J., Arndt, M. and Dicke, P. Feature linking via synchronization among distributed assemblies: simulations of results from cat visual cortex, Neural Comput. 2 (1990) 293-307.

4 Eeckman, F.H. and Freeman, W.J. Correlations between unit firing and EEG in the rat olfactory system, Brain Res. 528 (1990) 238-244.

5 Engel, A.K., K nig, P., Kreiter, A.K., Schillen, T.B. and Singer, W. Temporal coding in the visual cortex: New vistas on integration in the nervous system, Trends Neurosci. 15 (1992) 218-226.

6 Engel, A.K., K nig, P., Kreiter, A.K. and Singer, W. Interhemispheric synchronization of oscillatory neuronal responses in cat visual cortex, Science, 252 (1991) 1177-1179.

7 Engel, A.K., K nig, P. and Singer, W. Direct physiological evidence for scene segmentation by temporal coding, Proc. Natl. Acad. Sci. USA, 88 (1991) 9136-9140.

8 Freeman, W.J. and van Dijk, B.W. Spatial patterns of visual cortical fast EEG during conditioned reflex in a rhesus monkey, Brain Res. 422 (1987) 267-276.

9 Galambos, R., Makeig, S. and Talmachoff, P.J. A 40-Hz auditory potential recorded from the human scalp, Proc. Natl. Acad. Sci. USA, 78 (1981) 2643-2647.

10 Gray, C.M. Synchronous oscillations in neuronal systems: mechanisms and function, J. Comput. Neurosci. 1 (1994) 11-38.

11 Gray, C.M., K nig, P., Engel, A.K. and Singer, W. Oscillatory responses in cat visual cortex exhibit inter-columnar synchronization which reflects global stimulus properties, Nature, 338 (1989) 334-337.

12 Jefferys, J.G.R., Traub, R.D. and Whittington, M.A. Neuronal networks for induced "40 Hz" rhythms, Trends Neurosci. 19 (1996) 202-208.

13 Keller, I., Madler, C., Schwender, D. and Poppel, E. Analysis of oscillatory components in perioperative AEP-recordings: a nonparametric procedure for frequency measurement, Clin. Electroencephalogr. 21 (1990) 88-92.

14 Kulli, J. and Koch, C. Does anesthesia cause loss of consciousness, Trends Neurosci. 14 (1991) 6-10.

15 Llin s, R. and Ribary, U. Coherent 40-Hz oscillation characterizes dream state in humans, Proc. Natl. Acad. Sci. USA, 90 (1993) 2078-2081.

16 Madler, C., Keller, I., Schwender, D. and Poppel, E. Sensory information processing during general anaesthesia: effect of isoflurane on auditory evoked neuronal oscillations, Br. J. Anaesth. 66 (1991) 81-87.

17 Murthy, V.N. and Fetz, E.E. Coherent 25- to 35-Hz oscillations in the sensorimotor cortex of awake behaving monkeys, Proc. Natl. Acad. Sci. USA, 89 (1992) 5670-5674.

18 Pantev, C., Makeig, S., Hoke, M., Galambos, R., Hampson, S. and Gallen, C. Human auditory evoked gamma-band magnetic fields, Proc. Natl. Acad. Sci. USA, 88 (1991) 8996-9000.

19 Pfurtscheller, G., Flotzinger, D. and Neuper, C. Differentiation between finger, toe and tongue movement in man based on 40 Hz EEG, Electroencephalogr. Clin. Neurophysiol. 90 (1994) 456-460.

20 Ribary, U., Ioannides, A.A., Singh, K.D., Hasson, R., Bolton, J.P.R., Lado, F., Mogilner, A. and Llin s, R. Magnetic field tomography of coherent thalamocortical 40-Hz oscillations in humans, Proc. Natl. Acad. Sci. USA, 88 (1991) 11037-11041.

21 Sanes, J.N. and Donoghue, J.P. Oscillations in local field potentials of the primate motor cortex during voluntary movement, Proc. Natl. Acad. Sci. USA, 90 (1993) 4470-4474.

22 Singer, W. and Gray, C.M. Visual feature integration and the temporal correlation hypothesis, Annu. Rev. Neurosci. 18 (1995) 555-586.

23 Soltesz, I. and Desch nes, M. Low- and high-frequency membrane potential oscillations during theta activity in CA1 and CA3 pyramidal neurons of the rat hippocampus under ketamine-xylazine anesthesia, J. Neurophysiol. 70 (1993) 97-116.

24 Stumpf, C. The fast component in the electrical activity of rabbit's hippocampus, Electroencephalogr. Clin. Neurophysiol. 18 (1965) 477-486.

25 Tiitinen, H., Sinkkonen, J., Reinikainen, K., Alho, K., Lavikainen, J. and Naatanen, R. Selective attention enhances the auditory 40-Hz transient response in humans, Nature, 364 (1993) 59-60.

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