When a Brain Forgets Where Memory Is
Describes dissociative fugue- by far, one of the weirdest things that the brain is capable of.
Where does a thought go when it’s forgotten?
Sometimes, when I try to conjure a particular phrase, definition, or memory that is eluding me, I am struck by how very unfair it is that I have so much available in my brain and so little control over any of it.
Neurons integrate information from other neurons by summing excitatory and inhibitory input. If excitatory input exceeds a certain threshold, the receiving neuron fires and initiates a series of molecular changes that strengthens the synapses, or connections, from the input neurons. Donald Hebb (1949) famously used the catchphrase ‘cells that fire together wire together’ to describe the formation of cell assemblies through neuronal interactions. This process forms the basis for learning.
In the life span of the human female, no other naturally occurring hormone exposures are more extreme than those experienced during the perinatal period. Other, less extreme endocrine events, such as puberty and menopause, are associated with changes in human brain structure and function. Almost nothing is known about how the hormone exposures linked to reproductive experience influence the brain and behavior of human mothers. Rodent models have confirmed that reproduction produces neurological changes that persist throughout the life span and that these changes are not confined to those areas of the brain directly involved in maternal behaviors. For example, alterations have been observed also in brain regions associated with emotion (amygdala) and memory (hippocampus).
The existence of hormonal control of onset and maintenance of maternal behavior in nonhuman species (largely rodents) is well established. What little is known about humans is largely consistent with this literature, suggesting that in humans, too, the hormone exposures of pregnancy prime the maternal brain for the challenges of motherhood. Specifically, there are a small number of studies demonstrating that prenatal estrogen, cortisol, and oxytocin exposures influence the quality of early postpartum maternal care and the ability to respond to infant signals.
Species from rats to humans show a decline in physiological and behavioral responses to stress during pregnancy. Late in gestation, women exhibit a dampened cortisol response to HPA challenge and show decreased blood pressure, heart rate, and catecholamine responses to psychological and physical challenges. In parallel to these physiological changes, pregnant women also experience diminished psychological responses to stress. There is reason to believe that the down-regulation of stress responding during pregnancy serves an adaptive purpose, providing some protection for mother and fetus from the adverse effects of stress. It has been shown that early exposures to stress are more likely to result in preterm birth than are later exposures, and women who do not show the normative, protective decrease in stress responding during pregnancy are at increased risk for preterm delivery.
Up to 80% of women report impaired cognitive function during pregnancy. This observation is supported by empirical investigations of memory function during pregnancy. A meta-analysis of the 17 studies published over the last decade indicated deficits in two components of memory during pregnancy that persist into the postpartum period: recall memory and the executive component of working memory.