A relatively new technique in neuroscience, optogenetics, showed its potential this week by preventing recall of a specific memory in mice. Shining light into the brain through an optic cable deactivated genetically modified nerves in the hippocampus, meaning the mice no longer exhibited a learned fear response. Published by the UC Davis departments of Neuroscience and Psychology, this paper confirms a long untestable theory about how memories about places and events are recalled.
Mice were genetically modified so that their neurons expressed two proteins that were triggered when the neuron was stimulated; one that fluoresced green when the nerve was active, and one derived from the photosensistive eyespots in algae, that switches off activity in the neuron when it is exposed to light. Using this technique, neuroscientists can identify and switch off specific neurons involved in particular processes.
The green fluorescent proteins showed that when the mice were placed in a cage where they experienced a mild electric shock, neurons in the cortex, hippocampus, and amygdala activated to form a memory associating the cage with a fear. This memory induced a fear response if the cage is encountered again, using the same neurons. But if the nerves in the hippocampus were switched off using a beam of light, the mouse was not able to recall the memory and had normal behaviour.
This confirms the theory that during memory recall, the nerves that were involved in forming the memory are activated again so that the individual actually re-experiences the initial scenario, and that an important part of this memory formation and recall is the interaction between the cortex and the hippocampus.
Optogenetics is a promising new technique that is used more and more in neuroscience and psychology, and could broaden understanding of learning and memory.