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article imageNew light shed on emotional fear

By Tim Sandle     Dec 13, 2014 in Science
Bad experiences and unpleasant events can remain etched into the brain for a person’s entire life. A new study has identified the brain processes at work that enable ‘bad thoughts’ to remain.
The research was led by Joshua Johansen from the RIKEN Brain Science Institute in Japan. The results of the study have been published in the Proceedings of the National Academy of Sciences.
Scientists have identified a neural mechanism via which unpleasant experiences are translated into signals that trigger fear memories. This is through changing neural connections in a part of the brain called the amygdala. Neuroscientists believed that changes in the strength of the connections onto neurons in the central amygdala must occur for fear memory to be encoded.
The amygdala is an almond shaped mass of nuclei (mass of cells) located deep within the temporal lobe of the brain. In humans and other animals, this subcortical brain structure is linked to both fear responses and pleasure.
The research also supports an older theory into how the brain generates memories. This process is called Hebbian plasticity. Hebbian theory is a theory in neuroscience which proposes an explanation for the adaptation of neurons in the brain during the learning process. This is based around an increase the connection strength between neurons.
To explore the process, researchers studied if coincident electrical excitation of neurons (that store fear memories) is necessary to trigger changes in neural connections and memory formation. To demonstrate this, the scientists undertook animal experiments where they deployed a technique called optogenetics to silence electrical activity in a brain area called the amygdala, where fear memories are stored. Optogenetics uses light to control neurons which have been genetically sensitised to light.In 2010, optogenetics was chosen as the "Method of the Year" across all fields of science and engineering by the interdisciplinary research journal Nature Methods.
The researchers found that when they eliminated the shock and replaced it with optical excitation of amygdala neurons, no learning occurred. However, learning was restored when cell surface receptors for a neuromodulator called noradrenaline, which is important for attention, were activated at the same time.
The study went someway to explaining how aversive experiences are translated by the brain into emotional fear memories. In the longer-term, the findings may represent a general process to control memory formation in other brain areas and perhaps treat medically fearful anxiety or post-traumatic stress disorder.
The study was led by Joshua Johansen from the RIKEN Brain Science Institute in Japan and the research has been published in the journal PNAS, in a paper headed “Hebbian and neuromodulatory mechanisms interact to trigger associative memory formation.”
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