Tag Archives: Memory

Skull electrodes give memory a boost

The method can temporarily increase or decrease activity in a specific brain region and has already been shown to boost verbal and motor skills in volunteers.

Richard Chi of University of Sydney, and colleagues showed 36 volunteers a dozen “study” slides covered with shapes that varied in their number, arrangement, colour and size (see “Brain games”).

The volunteers were then shown five “test” slides – two with patterns that appeared in the study slides, two with completely new patterns and one whose pattern looked similar to that on a study slide.

Participants were asked to identify which of the test slides they had already seen, first performing the task without any brain stimulation.

Subjects then repeated the experiment 12 times, with one group receiving so-called anodal tDCS (which boosts activity) on their right ATL and cathodal tDCS (which inhibits activity) on their left.

A second group received the opposite stimulation and a third group received a placebo treatment, which did not stimulate either side of the brain.

Those in the first group more than doubled their scores after receiving tDCS, experiencing a 110 per cent improvement in visual memory. Participants in the second and third groups showed no overall improvement in performance.

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Neurons lose information at one bit per second

Information stored in the activity patterns of cerebral cortex neurons is discarded at the surprisingly high rate of one bit per active neuron per second, scientists from the Max Planck Institute for Dynamics and Self-Organization at the University of Gottingen and the Bernstein Center for Computational Neuroscience Gpttingen have found.

The new results obtained by the scientists in Göttingen have also revealed that the processes in the cerebral cortex are extremely chaotic. The fact that the researchers used a realistic model of the neurons in their calculations for the first time was crucial. When a spike enters a neuron, an additional electric potential forms on its cell membrane. The neuron only becomes active when this potential exceeds a critical value. “This process is very important,” says Fred Wolf, head of the Theoretical Neurophysics research group at the Max Planck Institute for Dynamics and Self-Organization. “This is the only way that the uncertainty as to when a neuron becomes active can be taken into account precisely in the calculations.”

Thanks to their more differentiated approach, the Göttingen-based researchers were able to calculate, for the first time, how quickly an activity pattern is lost through tiny changes; in other words, how it is forgotten. Approximately one bit of information disappears per active neuron per second. “This extraordinarily high deletion rate came as a huge surprise to us”, says Wolf. It appears that information is lost in the brain as quickly as it can be “delivered” from the senses.

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Scientists find link in humans between nerve cell production & memory

Production of new nerve cells in the human brain is linked to learning and memory, according to a new study from the University of Florida. The research is the first to show such a link in humans. The findings, published online and in an upcoming print issue of the journal Brain, provide clues about processes involved in age- and health-related memory loss and reveal potential cellular targets for drug therapy.

The researchers studied how stem cells in a memory-related region of the brain, called the hippocampus, proliferate and change into different types of nerve cells. Scientists have been unsure of the significance of that process in humans.

“The findings suggest that if we can increase the regeneration of nerve cells in the hippocampus we can alleviate or prevent memory loss in humans,” said Florian Siebzehnrubl, Ph.D., a postdoctoral researcher in neuroscience in the UF College of Medicine, and co-first author of the study. “This process gives us what pharmacologists call a ‘druggable target.’”

Over the past two decades, several studies have shown that new nerve cells are generated in the hippocampus. In animal studies, disrupting nerve cell generation resulted in the loss of memory function, while increasing the production of new nerve cells led to improved memory.

To investigate whether the same is true in humans, the UF researchers, in collaboration with colleagues in Germany, studied 23 patients who had epilepsy and varying degrees of associated memory loss. They analyzed stem cells from brain tissue removed during epilepsy surgery, and evaluated the patients’ pre-surgery memory function.

In patients with low memory test scores, stem cells could not generate new nerve cells in laboratory cultures, but in patients with normal memory scores, stem cells were able to proliferate. That showed, for the first time, a clear correlation between patient’s memory and the ability of their stem cells to generate new nerve cells.

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Know that noise? Scientists probe formation of auditory memories

Auditory perception requires the listener to learn recurring properties of complex sounds and associate them with plausible physical sources. “Most of our knowledge about auditory memory is based on simple sounds,” says lead study author Dr. Trevor Agus from the Ecole Normale Supérieure in Paris. “How templates emerge from everyday auditory experience with arbitrary complex sounds is currently largely unknown.”

Dr. Agus and colleagues used unpredictable, random hissing sounds, also known as noise, as a tool to observe the creation of new auditory memories in human listeners. Noise was particularly suitable for probing memory formation because the different sounds were acoustically complex, meaningless, and completely new to the listener.

Importantly, the listeners were unaware that identical copies of some of the noise samples would occasionally reoccur throughout the experiment.

The researchers discovered that repeated exposure induced learning for totally unpredictable and meaningless sounds. The listeners were better at detecting repetitions within noise samples that had been presented several times than new noise samples, showing that a new auditory memory had been created. “The sound memories were formed rapidly, with performance becoming abruptly near-perfect, and multiple noises were remembered for several weeks,” reports Dr. Agus.

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Seeing the Brain Hear Reveals Surprises About How Sound Is Processed

New research shows our brains are a lot more chaotic than previously thought, and that this might be a good thing. Neurobiologists at the University of Maryland have discovered information about how the brain processes sound that challenges previous understandings of the auditory cortex that suggested an organization based on precise neuronal maps.

Kanold and colleagues were able to look at the activity of all the neurons in a large region of the auditory cortex simultaneously. To get the highest resolution picture to date of how auditory cortex neurons are organized, the researchers used a technique to fill neurons in living mice with a dye that glows brightly when calcium levels rise, a key signal that neurons are firing. They then selectively illuminated specific regions of the cortex with a laser and measured the neuronal activity of hundreds of neurons in response to stimulation by simple tones of different frequencies.

“We discovered that the organization of the cortex does not look as pretty as it does in the textbooks, which surprised us,” explains Kanold. “Things are a lot messier than expected.” And we don’t see evidence of the maps previously proposed using less precise techniques.” But the disorder they found could indicate that the brain is far more adaptable than previously thought. “These results may rewrite our classical views of how cortical circuits are organized and what functions they serve,” suggests Dr. Shihab Shamma, whose previous research has involved mapping responses in the auditory cortex using traditional microelectrodes.

This suggests that there is very little redundancy in the function of cells in the auditory cortex, which differs notably from the visual cortex, in which neighboring neurons perform the same function as one another. This could be because our acoustic environment, such as the speech we hear, changes much faster than our visual environment, so we have to constantly adapt to new situations.

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