How brains remember and correct

Information processing in the brain is complex and involves both the processing of sensory inputs and the conversion of those inputs into behavior. The passing of electrical oscillations between networks of neurons in different parts of the brain is thought to be a critical component of cognition as well as conscious perception and awareness, but so far there has been little direct evidence linking specific neuronal oscillations to discrete thinking and behavior events. 

Jun Yamamoto and colleagues from the RIKEN–MIT Center for Neural Circuit Genetics have now detected a brief burst of nerve activity oscillating in two specific parts of the mouse brain just before a correct choice is made, either when planning an action or when correcting a mistake. 

The researchers searched for evidence of specific neuronal oscillations by studying mice navigating a T-shaped maze with a reward at the end of one arm of the T. Just before trained mice made the correct choice of direction, Yamamoto and his colleagues observed a brief burst of synchronized high-frequency gamma waves oscillating in specific parts of the entorhinal cortex and hippocampus. 

Yamamoto was fascinated to notice that the burst of gamma waves also occurred just before mice that had originally turned in the wrong direction realized their mistake and turned round. He called this the “oops” moment, and the results indicate that similar neuronal activity occurs when making a correct choice either immediately or on realization of an error. No such gamma-wave activity was detected when mice made the wrong choice without correcting it.

To further test the link between the gamma synchrony and the memory recall process, the researchers genetically engineered mice with light-activated ion channels that could block the gamma waves. When these channels were activated, the gamma waves ceased and the mice could no longer accurately choose the right direction or correct their wrong choices.

“Our work is telling us about how the brain recalls remembered information at critical moments,” says Yamamoto. “It suggests that synchronized gamma oscillations actually contribute to the animal’s correct choice rather than being a consequence of their choice.” The finding sheds light on the fundamental mechanism underlying the successful retrieval of working memory. Yamamoto now intends to see if these initial findings apply to other brain regions. 

The results also provide new insight into the phenomenon of animal consciousness. “Our findings provide evidence that animals employ a behavior monitoring process called metacognition that typically requires conscious awareness,” says Yamamoto.

Electrical stimulation of brain alters dreams

Nighttime dreams in which you show up at work naked, encounter an ax-wielding psychopath or experience other tribulations may become a thing of the past thanks to a discovery reported on Sunday.

Applying electrical current to the brain, according to a study published online in Nature Neuroscience, induces “lucid dreaming,” in which the dreamer is aware that he is dreaming and can often gain control of the ongoing plot.

The findings are the first to show that inducing brain waves of a specific frequency produces lucid dreaming.

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Neurons in the Brain Tune into Different Frequencies for Different Spatial Memory Tasks

Your brain transmits information about your current location and memories of past locations over the same neural pathways using different frequencies of a rhythmic electrical activity called gamma waves, report neuroscientists at The University of Texas at Austin.

The research, published in the journal Neuron on April 17, may provide insight into the cognitive and memory disruptions seen in diseases such as schizophrenia and Alzheimer’s, in which gamma waves are disturbed.

Previous research has shown that the same brain region is activated whether we’re storing memories of a new place or recalling past places we’ve been.

“Many of us leave our cars in a parking garage on a daily basis. Every morning, we create a memory of where we parked our car, which we retrieve in the evening when we pick it up,” said Laura Colgin, assistant professor of neuroscience and member of the Center for Learning and Memory in The University of Texas at Austin’s College of Natural Sciences. “How then do our brains distinguish between current location and the memory of a location? Our new findings suggest a mechanism for distinguishing these different representations.”

Memory involving location is stored in an area of the brain called the hippocampus. The neurons in the hippocampus that store spatial memories (such as the location where you parked your car) are called place cells. The same set of place cells are activated both when a new memory of a location is stored and, later, when the memory of that location is recalled or retrieved.

When the hippocampus forms a new spatial memory, it receives sensory information about your current location from a brain region called the entorhinal cortex. When the hippocampus recalls a past location, it retrieves the stored spatial memory from a subregion of the hippocampus called CA3.

The entorhinal cortex and CA3 transmit these different types of information using different frequencies of gamma waves. The entorhinal cortex uses fast gamma waves, which have a frequency of about 80 Hz (about the same frequency as a bass E note played on a piano). In contrast, CA3 sends its signals on slow gamma waves, which have a frequency of about 40 Hz.

Colgin and her colleagues hypothesized that fast gamma waves promote encoding of recent experiences, while slow gamma waves support memory retrieval.

They tested these hypotheses by recording gamma waves in the hippocampus, together with electrical signals from place cells, in rats navigating through a simple environment. They found that place cells represented the rat’s current location when cells were active on fast gamma waves. When cells were active on slow gamma waves, place cells represented locations in the direction that the rat was heading.

“These findings suggest that fast gamma waves promote current memory encoding, such as the memory of where we just parked,” said Colgin. “However, when we need to remember where we are going, like when finding our parked car later in the day, the hippocampus tunes into slow gamma waves.”

Because gamma waves are seen in many areas of the brain besides the hippocampus, Colgin’s findings may generalize beyond spatial memory. The ability for neurons to tune into different frequencies of gamma waves provides a way for the brain to traffic different types of information across the same neuronal circuits.

Colgin said one of the next steps in her team’s research will be to apply technologies that induce different types of gamma waves in rats performing memory tasks. She imagines that they will be able to improve new memory encoding by inducing fast gamma waves. Conversely, she expects that inducing slow gamma waves will be detrimental to the encoding of new memories. Those slow gamma waves should trigger old memories, which would interfere with new learning.