Theta and Gamma Oscillations during Encoding Predict Subsequent Recall

Electrophysiological and hemodynamic measures of human brain activity have been shown to distinguish between episodes of encoding items that are later recalled versus those that are not recalled (Paller and Wagner, 2002). Using intracranial recordings from 793 widespread cortical and subcortical sites in 10 epileptic patients undergoing invasive monitoring, we compared oscillatory power at frequencies ranging from 2 to 64 Hz as participants studied lists of common nouns. Significant increases in oscillatory power during encoding predicted subsequent recall, with this effect predominantly in the 4 – 8 Hz (theta) and 28 – 64 Hz (gamma) frequency bands. Sites exhibiting increased theta activity during successful encoding were clustered in right temporal and frontal cortex, whereas those exhib iting increased gamma activity appeared bilaterally at widespread cortical locations. These findings implicate theta and gamma oscillatory activity, across a widespread network of cortical regions, in the formation of new episodic memories.

Physiological activity during encoding must participate in transforming experience into a lasting trace that can later be recalled and recognized. Subsequent memory paradigms, in which online measures of neural activity as people encode items are segregated by the subsequent ability to recall or recognize those items, have helped to characterize the activity of different brain regions during memory formation (Paller and Wagner, 2002)…

Read the full article here Journal of Neuroscience (pdf)