40 Hz studies/Thalamus Theory

Magnetic field tomography of coherent thalamocortical 40-Hz

oscillations in humans

U. RIBARY*, A. A. IOANNIDESt, K. D. SINGHt, R. HASSONt, J. P. R. BOLTONt, F. LADO*, A. MOGILNER*,AND R. LLINAS*t

*Center for Neuromagnetism, Department of Physiology and Biophysics, New York University Medical Center, New York, NY 10016; and tDepartment of

Physics, The Open University, Milton Keynes, MK7 6AA, United Kingdom

Contributed by R. Llinds, July 30, 1991

Proc. Nati. Acad. Sci. USA Vol. 88, pp. 11037-11041, December 1991 Neurobiology

ABSTRACT

This paper introduces the use of magnetic field tomography (MFT), a noninvasive technique based on distributed source analysis of magnetoencephalography data,

which makes possible the three-dimensional reconstruction of dynamic brain activity in humans. MFE has a temporal resolution better than 1 msec and a spatial accuracy of 2-5 mm at the cortical level, which deteriorates to 1-3 cm at depths of 6 cm or more. MFT is used here to visualize the origin of a spatiotemporally organized pattern of coherent 40-Hz electrical activity. This coherence, initially observed during auditory

input, was proposed to be generated by recurrent corticothalamic oscillation. In support of this hypothesis, we illustrate well-defined 40-Hz coherence between corticalsubcortical sites with a time shift that is consistent with thalamocortical

conduction times. Studies on Alzheimer patients indicate that, while a similar activity pattern is present, the cortical component is reduced in these subjects.

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