Hippocampal sharp-wave ripples correlate with periods of naturally occurring self-generated thoughts in humans

Core features of human cognition highlight the importance of the capacity to focus on information distinct from events in the here and now, such as mind wandering. However, the brain mechanisms that underpin these self-generated states remain unclear. An emerging hypothesis is that self-generated states depend on the process of memory replay, which is linked to sharp-wave ripples (SWRs), which are transient high-frequency oscillations originating in the hippocampus. Local field potentials recorded over the hippocampus of 10 participants were explored to describe their association with ongoing thought patterns. The SWR rates were higher during extended periods of time when participants’ ongoing thoughts were vivid, less desirable, had more imaginable properties, and exhibited fewer correlations with an external task. These data suggest a role for SWR in the patterns of ongoing thoughts that humans experience in daily life.

Takamitsu Iwata, Takufumi Yanagisawa, Yuji Ikegaya, Jonathan Smallwood, Ryohei Fukuma, Satoru Oshino, Naoki Tani, Hui Ming Khoo, Haruhiko Kishima