We will be studying the limbic system (located below the brain) made of the hippocampus, the ventromedial prefrontal cortex, and the amygdala. Together, these complete the neural circuitry of stress.
The hippocampus (named after its resemblance to the seahorse, from the Greek, “seahorse” from hippos, “horse” and kampos, “sea monster”) is a major component of human brains and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus belongs to the limbic (Latin: limbus meaning border) system and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located under the cerebral cortex (allocortical) … It contains two main interlocking parts: the hippocampus proper (also called Ammon’s horn) and the dentate gyrus. Over the years, three main ideas of hippocampal function have dominated the literature: inhibition response, memory, and spatial.
As stated above from Wikipedia, one of its functions is to convert short term memory into long term memory. That is it takes memories stored in a temporary memory, processes it and places them into a permanent location.
This means that memories temporarily stored because of stress or trauma, are later processed and filed in the correct place. We call this process “Working through the memory”. It terms or PTSD, we are suddenly reliving the trauma. As long as we are not hurting anyone or ourselves, this is a good thing and we should not try to stop it. This is the brain sorting itself out so it can become healthy again.
The article then goes on to discuss the areas to which the hippocampi are connected. Of interest is the unidirectional flow from the entorhinal cortex (EC) and the connection to three or four layers of the cerebral cortex (memory).
In terms of anatomy, the hippocampus is an elaboration of the edge of the cerebral cortex, of the medial temporal lobe. The cortex thins from six layers to the three or four layers that make up the hippocampus.
The input to the hippocampus comes from the EC via the perforant path. The entorhinal cortex is strongly and reciprocally connected with many cortical and subcortical structures as well as with the brainstem.
The article mentioned that taxi drivers in NYC had larger dentate gyrus (The ‘head’ portion of the seahorse) but the overall size of the hippocampi remained constant. My greater interest in terms of the effect of stress on the brain is in the connection to the various brain levels and to the part of the brain which involves behavior. Damage to this produces unwelcomed behavior.
Several other connections play important roles in hippocampal function. Beyond the output to the EC, additional output pathways go to other cortical areas including the prefrontal cortex. A major output goes via the fornix to the lateral septal area and to the mammillary body of the hypothalamus (which the fornix interconnects with the hippocampus).
The article continues specifying important information that I did not take time to digest. However, if I were to take the time to understand this I am confident that it would explain why our behavior changes under the influence of trauma.
The final part of the paragraph reads:
The inputs from the septal area play a key role in controlling the physiological state of the hippocampus; destruction of the septal area abolishes the hippocampal theta rhythm and severely impairs certain types of memory.
That is the hard way of saying when we are under stress our memory is affected as well as our behavior.
Amygdalae