Chronic stress tied to impaired memory

Stress ball can’t remember what it did yesterday, so now it’s stressed.
Image courtesy of trasik555

Stress is a natural occurrence in life; however, chronic stress has been proven detrimental to one’s physical well being and here mental well-being. Researchers of the University of Minho, Portugal deemed chronic stress the cause of cortico-limbic impairment and (resulting) long-term memory block.

The cortico-limbic system consists of the amygdala, anterior thalamic nuclei, cerebrum, diencephalon, fornix, hippocampus, limbic cortex, midbrain, and septum. This string of brain controls behavior, emotion, long-term memory, motivation, and olfaction. Longer term memory itself is based on long term potentiation (LTP). This is basically a set of neurons firing consistently on a region increasing the neural receptors of the neuron across the synapse and that particular synapse’s strength. This concept ties closely to the electrical activity of the region.

This study measured the spectral coherence (synchronous electrical pattern) of the ventral hippocampus (vHIP) and medial prefrontal cortex (mPFC) as representers of the cortico-limbic system (vHIP and mPFC are linked by monosynaptic connection) in rats subject to no stress, short term stress (STS), or chronic unpredictable stress (CUS). The CUS group was exposed to 28 days of stress (1 hour/day) while the STS group only 6. Stressors were randomly chosen out of: 18°C water, overcrowding, exposure to hot air stream, noise, or shaking.

The study worked to prove stress induced dysfunction of the cortico-limbic system was due to regions of the brain being out of phase (out of sync) in neuronal firing patterns.

In measuring local field potentials, rats exposed to CUS showed increased power activity in the vHIP and mPFC as compared to STS induced rats and no stress controls. With this increased activity, a decrease in spectral coherence was seen between these two brain regions. The CUS rats had nearly a 50% decrease in phase coherence, while STS rats showed a roughly 20% drop as compared to controls.

Furthermore, LTP was seen as impaired in mice subject to stress. This was tested using the  Morris water maze to test spatial reference memory. Time to reach the platform was 65s (day one) and 30s (day four) compared to 50s (day one) and 20s (day four) of CUS and control rats respectively.

These results show chronic stress heavily disrupts coherence of regions of the cortico-limbic system, throws off neuronal interplay, and impairs cognitive function that relies on these out-of-sync areas, specifically memory. I guess that means my stressed friends might have aced their finals had they studied in a sauna…maybe.

Reference:
João Filipe Oliveira, Nuno Sérgio Dias, Mariana Correia, Filipa Gama-Pereira, Vanessa Morais Sardinha, Ana Lima, Ana Filipa Oliveira, Luís Ricardo Jacinto, Daniela Silva Ferreira, Ana Maria Silva, Joana Santos Reis, João José Cerqueira, Nuno Sousa. Chronic stress disrupts neural coherence between cortico-limbic structures. Frontiers in Neural Circuits, 2013.
http://dx.doi.org/10.3389/fncir.2013.00010

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