Hippocampal oscillations: Neural Interaction in Periods of Silence such as deep sleep.
Nikos Logothetis / Max Planck Institute for Biological Cybernetics.
While in deep dreamless sleep, our hippocampus sends messages to our cortex and changes its plasticity, possibly transferring recently acquired knowledge to long-term memory. 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 nonhuman primates 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 declarative memory is thought to occur in two subsequent steps. During the first step, the encoding phase, hippocampus rapidly binds neocortical representations to local memory traces, 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 neural basis of this hippocampal-cortical dialog, and how does hippocampus communicate with the rest of the brain?
Stephanie Bertenbreiter | Max-Planck-Institut
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