AI News, How Your Brain Remembers What You Had for Dinner Last Night

How Your Brain Remembers What You Had for Dinner Last Night

Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus of the human brain by distinct, sparse sets of neurons.

Encoding of episodic memories occurs in the hippocampus — a pair of small, seahorse-shaped regions located deep within the central portion of the brain — but the precise mechanism and numbers of neurons involved has been unclear.

“For example, degeneration in this region of the brain is responsible for memory loss in the early stages of Alzheimer’s disease.” Wixted, with Larry Squire, PhD, Distinguished Professor of Psychiatry, Neurosciences and Psychology in UC San Diego School of Medicine, and colleagues studied brain function in 20 epileptic patients undergoing intracranial monitoring for clinical purposes.

The scientists found that individual episodic memories are encoded and represented by the strong activity of small (fewer than 2.5 percent) and usually non-overlapping sets of hippocampal neurons, a finding that perhaps helps explain why past research efforts have struggled to detect the process.

Episodic Memory Formation In The Hippocampus

In a fascinating new study, a team of researchers based at the University of California, San Diego describe experimental findings that shed light on the neural mechanisms behind episodic memory formation in the human brain.

More specifically, they found that each memory is encoded, or created, within a small fraction of distributed neurons within the hippocampus and that individual neurons are committed to a small number of memories.

Computational models suggested that each memory was likely to be coded by a small fraction of distributed hippocampal neurons but there was no experimental evidence to back this up, and whether each individual neuron is responsible for one or multiple episodic memories remained unknown. 

The individuals were first given a list of words to memorize and were then presented with a longer list of words that contained previously studied words (targets) and new words (foils).

Furthermore, the researchers discovered that the targets were coded in a sparsely distributed fashion throughout the hippocampus with around 2% of cells responding to any one target and 3% of targets eliciting a strong firing response in any one neuron.

Storing Memories of Recent Events

Memories of recent events may be held by a small number of neurons distributed across the brain’s hippocampus, a new study suggests.

In a sparse distributed scheme, each memory would be coded by the activity of a small proportion of neurons, and each neuron would contribute to a few memories.

The scientists were able to explore the mechanisms of memory at the single-neuron level by studying the brains of 9 patients with severe epilepsy who were being treated at the Barrow Neurological Institute.

They then took a word recognition test with 32 targets from the study list and 32 “foils” that weren’t on the list.

If the items had been presented many times, the results might simply highlight neurons that respond to long-established semantic memories, rather than to words recently studied.

“To really understand how the brain represents memory, we must understand how memory is represented by the fundamental computational units of the brain—single neurons—and their networks,” Steinmetz says.

“Knowing the mechanism of memory storage and retrieval is a critical step in understanding how to better treat the dementing illnesses affecting our growing elderly population.” —by Harrison Wein, Ph.D.

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