Learning Objectives

The large majority of human neuroscience research on long-term memory has focused on identifying the spatial locations of activity associated with this process (see Chapter 3). Although the temporal dimension of brain activity is often ignored, this does not mean that brain activity is static across time. In reality, brain activity changes rapidly across time, and the temporal dynamics of activity must be tracked to understand the brain mechanisms underlying memory. This chapter focuses on the timing of brain activity associated with long-term memory. As discussed previously (see Chapters 1 and 3), recollection refers to retrieval of detailed information, whereas familiarity refers to retrieval of non-detailed information. The chapter begins by introducing event-related potential (ERP) activations (see Chapter 2) that have been associated with familiarity and recollection (section 4.1). Familiarity has been associated with activity in frontal brain regions that occurs within 300 to 500 milliseconds after stimulus onset, while recollection has been associated with activity in parietal brain regions that occurs within 500 to 800 milliseconds after stimulus onset. In section 4.2, a scientific debate that has focused on the ERP activity associated with familiarity is discussed. In section 4.3, it is shown that synchronous activity in two different brain regions (i.e., activation timecourses that increase and decrease together) indicates that these regions interact. Such synchronous activity between regions during long-term memory typically occurs within specific frequency bands of activity including the theta frequency band (4 to 8 cycles per second, i.e., Hertz), the alpha frequency band (8 to 12 Hertz), and the gamma frequency band (greater than 30 Hertz). Theta activity reflects the interaction between the hippocampus and cortical regions during long-term memory, alpha activity reflects inhibition of cortical regions, and gamma activity reflects processing of features in different cortical regions that are combined to create a unified memory.