Memory – and the stuff of dreams

Can you remember when you heard about 9/11? Chances are you’ll be flooded instantly with memories — not only where you were, but what you were doing, who you were with, what you could smell and see at the time as well as how you felt.

How does that happen? In the first half of this fascinating book, Dr Veronica O’Keane explains the neurological pathways and processes involved in memory. We are constantly receiving stimuli from our environment via the five senses of sight, sound, smell, taste and touch. These sensations travel via cells called neurons which are electrically activated and release various transmitters into the spaces between them and other neurons, which are then taken up and cause that neuron in turn to become stimulated. We are also continually receiving internal stimuli from our bodies — organs such as the gut, heart and lungs. Sensations from our senses enter through sensory neurons in the eye, ear, nose, tongue, skin and mucus membranes, and travel to the relevant part of the cerebral hemispheres in our brain. The sensations from our body converge on a part of the brain called the insula.

All of these eventually end up being processed in the hippocampus, and from there selective memories are integrated during REM sleep into the prefrontal cortex just above our eyes. As the hippocampal neurons bombard the prefrontal ones during REM sleep, shards of old memories are activated, leading to dreams. Perhaps the function of dreams is to remind and warn us of the past.

Biographical memories remain consolidated in the pre-frontal cortex, although they are also subject to reprocessing when we recall them and re-store them in a slightly different way. Drawing on them and on sensory memories elsewhere in the cortex leads to learning, insight and wisdom.

Sensate memories being processed in the hippocampus are augmented by emotions, which arise from the amygdala, hypothalamus and insula, after they have received input from the sensory cortices.