Neural interaction in periods of silence

November 21, 2012
This shows oscillations in the hippocampus: neural interactions during non-REM sleep and periods of silence. Credit: MPI for Biological Cybernetics

German neurophysiologists have developed a new method to study widespread networks of neurons responsible for our memory.

While in deep dreamless sleep, our hippocampus sends messages to our cortex and changes its plasticity, possibly transferring recently acquired knowledge to . But how exactly is this done? Scientists from the Max Planck Institute for Biological Cybernetics have now developed a novel multimodal methodology called "neural event-triggered functional magnetic resonance imaging" (NET-fMRI) and presented the very first results obtained using it in experiments with both anesthetized and awake, behaving monkeys. The new methodology uses multiple-contact electrodes in combination with functional magnetic resonance imaging (fMRI) of the entire brain to map widespread networks of neurons that are activated by local, structure-specific neural events.

Many invasive studies in and clinical investigations in human patients have demonstrated that the hippocampus, one of the oldest, most primitive brain structures, is largely responsible for the long term retention of information regarding places, specific events, and their contexts, that is, for the retention of so-called declarative memories. Without the hippocampus a person may be able to learn a manual task over a period of days, say, playing a simple instrument, but – remarkably – such a skill is acquired in the absence of any memory of having practiced the task before.

The consolidation of is thought to occur in two subsequent steps. During the first step, the encoding phase, hippocampus rapidly binds neocortical representations to local , while during subsequent "off-line" periods of calmness or sleep the new traces are concurrently reactivated in both hippocampus and cortex to strengthen the cortico-cortical connections underlying learned representations. But what is the of this hippocampal-cortical dialog, and how does hippocampus communicate with the rest of the brain?

For the very first time, Nikos Logothetis, director of the Department for Physiology of Cognitive Processes at the Max Planck Institute for and his team used so-called neural event triggered (NET-fMRI) in both anesthetized and awake, behaving monkeys to characterize the brain areas that consistently increased or decreased their activity in relationship to a certain type of fast hippocampal oscillations known as ripples. Ripples occur primarily during deep sleep and can be measured with electrophysiological methods. Using intracranial recordings of field potentials, the scientists demonstrated that the short periods of aperiodic, recurrent ripples are closely associated with reproducible cortical activations that occur concurrently with extensive activity suppression in other brain structures.

Interestingly, structures were suppressed whose activities could, in principle, interfere with the hippocampal-cortical dialog. The suppression of activity in the thalamus, for instance, reduces signals related to sensory processing, while the suppression of the basal ganglia, the pontine region and the cerebellar cortex may reduce signals related to other memory systems, such as that underlying procedural learning, for example riding a bicycle.

The aforementioned findings offer revealing insights into the large-scale organization of memory, a cognitive capacity emerging from the activation of widespread neural networks which were impossible to study in depth before now using either functional imaging alone or traditional single neuron recordings. Capacities such as perception, attention, learning and memory are actually best investigated using multimodal methodologies such as the NET-fMRI method employed in the MPI study. It is difficult to overstate the importance of the study of the neural mechanisms underlying such capacities, as the vast majority of neurological failures actually reflect dysfunctions of large-scale networks, including cortical and subcortical structures.

Explore further: How connections in the brain must change to form memories could help to develop artificial cognitive computers

More information: Logothetis, N.K., Eschenko, O., Murayama, Y., Augath, M., Steudel, T., Evrard, H.C., Besserve, M., Oeltermann, A. (2012) Hippocampal-cortical Interaction during Periods of Subcortical Silence. Nature, doi: 10.1038/nature11618

Related Stories

How connections in the brain must change to form memories could help to develop artificial cognitive computers

November 7, 2012
Exactly how memories are stored and accessed in the brain is unclear. Neuroscientists, however, do know that a primitive structure buried in the center of the brain, called the hippocampus, is a pivotal region of memory formation. ...

Reduction of excess brain activity improves memory in amnestic mild cognitive impairment

May 9, 2012
Research published in the May 10 issue of the journal Neuron, describes a potential new therapeutic approach for improving memory and modifying disease progression in patients with amnestic mild cognitive impairment. The ...

Recommended for you

The neural codes for body movements

July 21, 2017
A small patch of neurons in the brain can encode the movements of many body parts, according to researchers in the laboratory of Caltech's Richard Andersen, James G. Boswell Professor of Neuroscience, Tianqiao and Chrissy ...

Faulty support cells disrupt communication in brains of people with schizophrenia

July 20, 2017
New research has identified the culprit behind the wiring problems in the brains of people with schizophrenia. When researchers transplanted human brain cells generated from individuals diagnosed with childhood-onset schizophrenia ...

Scientists discover combined sensory map for heat, humidity in fly brain

July 20, 2017
Northwestern University neuroscientists now can visualize how fruit flies sense and process humidity and temperature together through a "sensory map" within their brains, according to new research.

Scientists reveal how patterns of brain activity direct specific body movements

July 20, 2017
New research by Columbia scientists offers fresh insight into how the brain tells the body to move, from simple behaviors like walking, to trained movements that may take years to master. The discovery in mice advances knowledge ...

Team traces masculinization in mice to estrogen receptor in inhibitory neurons

July 20, 2017
Researchers at Cold Spring Harbor Laboratory (CSHL) have opened a black box in the brain whose contents explain one of the remarkable yet mysterious facts of life.

Speech language therapy delivered through the Internet leads to similar improvements as in-person treatment

July 20, 2017
Telerehabilitation helps healthcare professionals reach more patients in need, but some worry it doesn't offer the same quality of care as in-person treatment. This isn't the case, according to recent research by Baycrest.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Tausch
not rated yet Nov 22, 2012
Congratulations.
Without the hippocampus a person may be able to learn a manual task over a period of days, say, playing a simple instrument, but – remarkably – such a skill is acquired in the absence of any memory of having practiced the task before.

Correct. Kudos.
Imagine a newborn's first breath as "task".
A newborn's sleep is proportionally the greatest time factor of all 'activities'(besides breathing.)
A possible insight from your research to explain SIDS -
Sudden infant death syndrome.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.