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Coherence of gamma-band EEG activity as a basis for associative learning


Different regions of the brain must communicate with each other to provide the basis for the integration of sensory information, sensory-motor coordination and many other functions that are critical for learning, memory, information processing, perception and the behaviour of organisms. Hebb1 suggested that this is accomplished by the formation of assemblies of cells whose synaptic linkages are strengthened whenever the cells are activated or ‘ignited’ synchronously. Hebb's seminal concept has intrigued investigators since its formulation, but the technology to demonstrate its existence had been lacking until the past decade. Previous studies have shown that very fast electroencephalographic activity in the gamma band (20–70 Hz) increases during, and may be involved in, the formation of percepts and memory2,3,4,5,6, linguistic processing7, and other behavioural and preceptual functions8,9,10,11,12. We show here that increased gamma-band activity is also involved in associative learning. In addition, we find that another measure, gamma-band coherence, increases between regions of the brain that receive the two classes of stimuli involved in an associative-learning procedure in humans. An increase in coherence could fulfil the criteria required for the formation of hebbian cell assemblies1, binding together parts of the brain that must communicate with one another in order for associative learning to take place. In this way, coherence may be a signature for this and other types of learning.

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Figure 1: Pairs of electrode sites displaying significantly greater coherence in the 37–43-Hz gamma band during CS+ than during CS trials in the 2,750–3,000-ms time window for the 120 acquisition trials.
Figure 2: Difference in evoked-response-potential waves between CS+ and CS at each electrode involved in response to the UCS when the UCS was administered to the left (grey line) and right (black line) midfingers.


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We thank I. Gutberlet for assistance in data analysis. This research was supported by a grant from the Deutsche Forschungsgemeinschaft to W.H.R.M. and a grant from the Rehabilitation Research and Development service, US Department of Veterans Affairs to E.T.

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Miltner, W., Braun, C., Arnold, M. et al. Coherence of gamma-band EEG activity as a basis for associative learning. Nature 397, 434–436 (1999).

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