A recent review by the late, great Howard Eichenbaum.  You’ll be missed, Howard.

Eichenbaum, H. (2017). Memory: organization and control. Annual review of psychology, 68, 19-45.

Takeda et al show that layer-specific oscillatory synchrony during successful recall of memories.  Specifically, there was laminar specific feedback from area 36 to area TE that supported the recall of a paired associate object.

Frequency-specific hippocampal-prefrontal interactions during associative learning
Brincat, S.L. and Miller, E.K. (2015) Nature Neuroscience, advanced online publication

Much of our knowledge of the world depends on learning associations (for example, face-name), for which the hippocampus (HPC) and prefrontal cortex (PFC) are critical. HPC-PFC interactions have rarely been studied in monkeys, whose cognitive and mnemonic abilities are akin to those of humans. We found functional differences and frequency-specific interactions between HPC and PFC of monkeys learning object pair associations, an animal model of human explicit memory. PFC spiking activity reflected learning in parallel with behavioral performance, whereas HPC neurons reflected feedback about whether trial-and-error guesses were correct or incorrect. Theta-band HPC-PFC synchrony was stronger after errors, was driven primarily by PFC to HPC directional influences and decreased with learning. In contrast, alpha/beta-band synchrony was stronger after correct trials, was driven more by HPC and increased with learning. Rapid object associative learning may occur in PFC, whereas HPC may guide neocortical plasticity by signaling success or failure via oscillatory synchrony in different frequency bands.

MIT News Office: Neurons hum at different frequencies to tell the brain which memories it should store.
New discovery from the Miller Lab

Anne Trafton | MIT News Office
February 23, 2015
Our brains generate a constant hum of activity: As neurons fire, they produce brain waves that oscillate at different frequencies. Long thought to be merely a byproduct of neuron activity, recent studies suggest that these waves may play a critical role in communication between different parts of the brain.

A new study from MIT neuroscientists adds to that evidence. The researchers found that two brain regions that are key to learning — the hippocampus and the prefrontal cortex — use two different brain-wave frequencies to communicate as the brain learns to associate unrelated objects. Whenever the brain correctly links the objects, the waves oscillate at a higher frequency, called “beta,” and when the guess is incorrect, the waves oscillate at a lower “theta” frequency. Read more

Recent studies have suggested that beta-band oscillatory synchrony plays a role in cognition.  For example, different networks of neurons in the prefrontal cortex dynamically synchronize at beta as animals switch between two different task rules (Buschman et al., 2012) suggesting that beta synchrony is forming the neural ensembles for the rules.  Different items simultaneously held in working memory line-up on different phases of beta/low-gamma oscillations, as if the brain is juggling the two items 30 times a second (Siegel et al., 2009).  Hanslmayr et al disrupted these fine temporal relations by stimulating the human with beta-band TMS pulses.   Beta stimulation of the left inferior frontal gyrus impaired memory formation while stimulation at other frequencies did not.  There was a beta “echo” that outlasted the stimulation.  Subjects with better beta entrainment showed more memory impairment.  This lends support for the role of beta rhythms in cognition by showing a causal relationship between beta desynchrony and memory.

This paper:
Simon Hanslmayr, Jonas Matuschek, Marie-Christin Fellner, Entrainment of Prefrontal Beta Oscillations Induces an Endogenous Echo and Impairs Memory Formation, Current Biology, Available online 27 March 2014, ISSN 0960-9822

Buschman, T.J., Denovellis, E.L., Diogo, C., Bullock, D. and Miller, E.K. (2012) Synchronous oscillatory neural ensembles for rules in the prefrontal cortex. Neuron, 76: 838-846.  View PDF

Siegel, M., Warden, M.R., and Miller, E.K. (2009) Phase-dependent neuronal coding of objects in short-term memory. Proceedings of the National Academy of Sciences, 106: 21341-21346. View PDF »  Read commentary by Vogel and Fukuda

An excellent review by Matt Shapiro and crew on an important topic.  They discuss complementary roles and bidirectional interactions between the prefrontal cortex and hippocampus.

Newman et al used the drug scopolamine to disrupt theta-gamma coupling in the medial entorhinal cortex of rats. Gamma power at the peak of theta was reduced and shifted to subsequent phases.  Scopolamine also seemed to reduce the rats’ familiarity with the testing enclosure. The data support the hypothesis that memory encoding and retrieval occur at different theta phases.

Miguel Remondes and Matt Wilson show that theta synchrony between the hippocampus and anterior cingulate during a task in which rats chose one of four trajectories.  Theta coherence at 8 Hz lowers slightly (by 1 Hz) when rats enter the decision phase of the task and hippocampal processing of trajectory information precedes that of the anterior cingulate.  Thus, lowering of theta synchrony may coordinate the integration of hippocampal information by neurons in the anterior cingulate.

Eyewitness testimony is shockingly unreliable.  How unreliable?  Ask Elizabeth Loftus.

A review in Science of Sue Corkin’s book on the famous neuropsychology patient H.M., who could no longer form memories after his hippocampus was removed.

Permanent Present Tense The Unforgettable Life of the Amnesic Patient, H.M. by Suzanne Corkin Basic Books, New York, 2013. 400 pp. $28.99, C$32. ISBN 9780465031597. Allen Lane, London. £20. ISBN 9781846142710.

A flurry of articles about Picower Institute’s Susumu Tonegawa’s paper implanting false memories in the mouse brain. They identified and tagged a memory engram for one environment, then activated that engram in a different environment while pairing it with shock.  Later, the animals showed fear in the first environment as if they were shocked there.
The Guardian
The New York Times
The cover of Science

The paper: Creating a false memory in the hippocampus