Human hippocampal theta oscillations: Distinctive features and interspecies commonalities

14 The hippocampus, along with its characteristic theta oscillation, has been widely implicated in various 15 aspects of animal memory and behavior. Given the important roles that hippocampal theta oscillations have 16 in theoretical models of brain function, it might be considered surprising that these signals have not been 17 reported as often in humans as in animals. In this chapter we review recent research on hippocampal theta 18 oscillations in humans, focusing on brain recordings from neurosurgical patients, which provides a key 19 opportunity for observing hippocampal oscillations during cognition. The emerging theme of this body of 20 work is that humans do indeed have hippocampal oscillations that are similar overall compared to the theta 21 oscillation that is commonly found in rodents. Most notably, the human theta oscillation exhibits correlations 22 with sensorimotor, navigation, and memory processing in the same general fashion as expected from rodents. 23 However, some of the details of theta’s relationship with behavior differ significantly compared to such 24 signals in rodents—such as having a lower amplitude, frequency, and duration—which can make this signal 25 less readily observable. Thus, theta oscillations are a key component of hippocampal processing in humans, 26 but the patterns it exhibits compared to rodents points out distinctive aspects of human brain processes. 27