ScienceDaily has an item (here) on a paper by L Schwabe, M Tegenthoff, O Höffken, O Wolf; Mineralocorticoid Receptor Blockade Prevents Stress-Induced Modulation of Multiple Memory Systems in the Human Brain; Biological Psychiatry, 2013. It examines the switch from conscious learning to unconscious learning under stress conditions.

 

 

Conscious learning involves the hippocampus and declarative memory while unconscious learning involves the dorsal striatum and procedural memory. Stress causes alterations of amygdala connectivity with hippocampus and dorsal striatum to shift the learning method towards unconscious learning. Performance in learning tasks that can be learned both ways do not appear to be affected by this shift.

 

 

The researchers used a weather forecasting ‘game’ to measure performance. The subjects can work out how to do the forecasting through trial and error, either with conscious problem solving or by going with their gut feeling. They found that by blocking a particular receptor type, mineralocorticoid receptors, this switch under stress by adrenal cortex hormones no longer happened and performance suffered as a result.

 

 

Here is part of the abstract:

 

Accumulating evidence suggests that stress may orchestrate the engagement of multiple memory systems in the brain. In particular, stress is thought to favor dorsal striatum-dependent procedural over hippocampus-dependent declarative memory. However, the neuroendocrine mechanisms underlying these modulatory effects of stress remain elusive, especially in humans. Here, we targeted the role of the mineralocorticoid receptor (MR) in the stress-induced modulation of dorsal striatal and hippocampal memory systems in the human brain using a combination of event-related functional magnetic resonance imaging and pharmacologic blockade of the MR.

 

Our findings indicate that the stress-induced shift from hippocampal to dorsal striatal memory systems is mediated by the amygdala, required to preserve performance after stress, and dependent on the MR.

 

 

It seems to me that learning during stress would be particularly important to survival but at the same time it may be that conscious resources are particularly stretched during stress – conscious learning might then be unreliable and moving learning to a more unconscious mode could be very advantageous. On the other hand there could be reasons for this that have to do with partially suppressing memories of stressful events so that the learning is not too painful to acquire. Perhaps it has to do with how the amygdala functions under stress as opposed to normally and is just one of a suite of related changes to memory under stress.