Cortical oscillations during encoding predict successful recall

Sederberg, P. B.1, Madsen, J. R.2,3, and Kahana, M. J.1
1Volen Center for Complex Systems, Brandeis University, Waltham, MA; 2Department of Neurosurgery; Childrens' Hospital Boston, MA; 3Department of Surgery, Harvard Medical School, Boston, MA

Successful formation of new episodic memories is associated with a variety of physiological markers (Paller and Wagner, 2002). Recent work has shown that gamma phase synchrony in medial temporal lobe (MTL) during study predicts subsequent recall (Fell et al., 2001). Recording intracranially from 793 widespread cortical and subcortical sites in 10 epileptic patients undergoing invasive monitoring, we examined oscillatory power at frequencies ranging from 2 to 64Hz as participants studied lists of common nouns. Results showed that significant increases in oscillatory power in the 4-8 Hz (theta) and 28-64 Hz (gamma) frequency ranges predicted successful retrieval of list items. At some sites, oscillatory activity, primarily in 9-28 Hz range, decreased with successful encoding. Electrodes exhibiting increases in theta oscillations that predicted successful recall clustered in the right temporal and frontal lobes. Sites where gamma oscillations positively correlated with subsequent recall were found at many cortical locations, but especially in the temporal lobe and subtemporal occipital region. These findings point to a widespread network of cortical regions whose activity is modulated during successful episodic memory formation.