How the olfactory brain affects memory
April 29, 2019
Science Daily/Ruhr-University Bochum
How sensory perception in the brain affects learning and memory processes is far from fully understood. Two neuroscientists of Ruhr-Universität Bochum (RUB) have discovered a new aspect of how the processing of odours impacts memory centres. They showed that the piriform cortex -- a part of the olfactory brain -- has a direct influence on information storage in our most important memory structure, the hippocampus. Dr. Christina Strauch and Professor Denise Manahan-Vaughan report about their findings in the online edition of the magazine Cerebral Cortex on 9 April 2019.
Electric impulses simulate odours
To find out how odours affect memory formation, the researchers triggered an artificial perception of an odour in the brains of rats. To do this, they stimulated the piriform cortex with electrical impulses. "We were very surprised to see that the hippocampus directly responds to stimulation of the piriform cortex," remarked Christina Strauch.
The hippocampus uses sensory information to create complex memories. The basis of this processes is its ability to increase the efficacy of information transmission across synapses and thereby store memory contents. This process is called synaptic plasticity. Manahan-Vaughan and Strauch were the first to show that stimulation of the anterior piriform cortex triggers synaptic plasticity in the hippocampus.
Special role for olfaction
In a second step, the researchers examined to what extent the piriform cortex competes with the entorhinal cortex in driving hippocampal synaptic plasticity. This structure sends information about activity in all sensory modalities to the hippocampus. Activating the afferent pathway of this structure, called the perforant path, triggered completely different reaction patterns in the hippocampus, to those generated by the piriform cortex. "The study gives us a theoretical basis for understanding how olfaction plays such a special role in memory formation and retrieval," commented Denise Manahan-Vaughan.
https://www.sciencedaily.com/releases/2019/04/190429125422.htm
Sleep readies synapses for learning
Findings offer insight into changes that occur in the brain during sleep
July 1, 2019
Science Daily/Society for Neuroscience
Synapses in the hippocampus are larger and stronger after sleep deprivation, according to new research in mice published in JNeurosci. Overall, this study supports the idea that sleep may universally weaken synapses that are strengthened from learning, allowing for new learning to occur after waking.
Sleep is thought to recalibrate synaptic strength after a day of learning, allowing for new learning to take place the next day. Chiara Cirelli and colleagues at the University of Wisconsin-Madison examined how synapses in the hippocampus, a structure involved in learning, changed following sleep and sleep deprivation in mice.
Consistent with previous studies in the cortex, the researchers observed that synapses were larger, and therefore stronger, after the mice were awake for six to seven hours compared to after they were asleep for the same amount of time. Additionally, the researchers found that the synapses were strongest when the mice were forced to stay awake and interact with new stimuli, compared to mice that stayed awake on their own. This is consistent with the hippocampus' role in learning, and suggests that synaptic changes take place when learning occurs, not merely from being awake.
https://www.sciencedaily.com/releases/2019/07/190701144310.htm