NONINVASIVE DETECTION OF ONGOING NEURONAL POPULATION ACTIVITY IN NORMAL HUMAN HIPPOCAMPUS

A 122-channel magnetoencephalographic array was used to monitor ongoin g neuronal population activity in six normal human subjects during the performance of a mental calculation and passive viewing of a picture. Signal-space projection was utilized to obtain waveforms and spectra for activity in anterior hippocampus and sensorimotor cortex. Hippocam pal waveforms were complex. Spectral components below 12 Hz in hippoca mpus included task-dependent peaks superimposed on a broadband backgro und of increasing amplitude at decreasing frequencies. MEG imaging of both waveforms and spectra for ongoing activity within hippocampus mak es possible the investigation of the role of rhythmic and non-rhythmic hippocampal activity in normal human cognition.