Coupled ripple oscillations between the medial temporal lobe and neocortex retrieve human memory
Coupled ripples in memory Short lived, high frequency oscillations in the brain called ripples have been implicated as substrates for memory formation. There is, however, little evidence linking ripple activity with awake memory retrieval in humans. Vaz et al. analyzed intracranial recordings in human subjects (see the Perspective by Gelinas) They found that ripple oscillations in the brain's medial temporal lobe were coupled with ripple oscillations in the temporal cortex. This coupling was enhanced just before successful memory retrieval. During successful retrievals with ripples, patterns of oscillations were recapitulated across multiple electrodes, consistent with the initial encoding. The observation that ripple oscillations occur before successful memory retrieval suggests that they may play a mechanistic role in the retrieval process. Science, this issue p. 975; see also p. 927 Intracranial EEG recordings successfully reveal the link between ripple oscillations and memory retrieval in the awake human brain. Episodic memory retrieval relies on the recovery of neural representations of waking experience. This process is thought to involve a communication dynamic between the medial temporal lobe memory system and the neocortex. How this occurs is largely unknown, however, especially as it pertains to awake human memory retrieval. Using intracranial electroencephalographic recordings, we found that ripple oscillations were dynamically coupled between the human medial temporal lobe (MTL) and temporal association cortex. Coupled ripples were more pronounced during successful verbal memory retrieval and recover the cortical neural representations of remembered items. Together, these data provide direct evidence that coupled ripples between the MTL and association cortex may underlie successful memory retrieval in the human brain.
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