Bernstein member involved: Denise Manahan-Vaughan

Researchers at the Ruhr University Bochum have investigated how two brain areas influence the nature of memory content. The team from the Department of Neurophysiology showed in rats how the so-called locus coeruleus and the ventral tegmental area sustainably alter brain activity in the hippocampus, which is crucial for memory. The influences of the two areas are in competition with each other and determine, for example, how emotionally charged or relevant experiences are stored. Dr. Hardy Hagena and Prof. Dr. Denise Manahan-Vaughan used optogenetics for the study. They genetically modified rats so that certain nerve cells could be activated or deactivated with light. They describe the results in the journal PNAS, short for Proceedings of the National Academy of Sciences, dated December 30, 2024.

The basis of learning

Neurotransmitters such as dopamine and norepinephrine play a crucial role in information processing. They can alter the communication ability of nerve cells for a long time; this is called synaptic plasticity, which in turn encompasses the cellular basis of memory formation. In the case of long-term potentiation, the communication ability of the affected synapses increases; in the case of long-term depression of synaptic transmission, the activity of certain synapses in the hippocampus is reduced. Thus, experiences can be stored and updated.

The locus coeruleus and the ventral tegmental area release neurotransmitters into the hippocampus, where learning processes take place. Until now, it was unclear to what extent these regions play a role in synaptic plasticity and thus also in learning processes. It is known that the ventral tegmental area is important for reward and aversion reactions. The locus coeruleus, on the other hand, is crucial for the perception of novel stimuli and thus controls attention.

How memory formation in the hippocampus is influenced

Hagena and Manahan-Vaughan recorded the activity of synapses in the hippocampus of rodents. The animals were genetically modified so that the activity of certain cells in the locus coeruleus and the ventral tegmental area could be inhibited or stimulated with light. When the ventral tegmental area was activated, this led to long-term potentiation in the hippocampus. Activation of the locus coeruleus had the opposite effect.

When the team inactivated the ventral tegmental area in behavioral experiments, long-term potentiation in the hippocampus was suppressed during exploration of a new environment.

When the researchers inactivated the locus coeruleus, long-term depression was suppressed during exploration of the environment.

The hippocampus can process various aspects of spatial information through long-term potentiation and long-term depression. The researchers have now identified the physiological process by which these changes in synaptic plasticity can be controlled.

Process determines the nature of memory content

“We were surprised that the effects were so specific,” says Hardy Hagena. ”The fact that the ventral tegmental area and the locus coeruleus produce these two different types of synaptic plasticity gives us insight into how motivation and attention influence synaptic responses relative to their relevance and current memory content.”

Translated with DeepL