I start the column with an old story, the introduction of which might have been forgotten in the police pages of a now-defunct periodical. However, it unfolded unpredictably and changed the course of science.
The beginning: an angry man approached a girl and said he was going to throw her into a sack full of poisonous snakes.
From then on, the child started to have recurrent nightmares in which he was trapped with the vipers. When approaching adolescence, for other reasons, she became epileptic. His convulsions were preceded by haunting reminiscences of lived threat, more visions of snakes.
The girl received medical treatment, however the medications did not prevent further epileptic attacks. The only therapy left was to surgically remove the root of her problem. Therefore, the young woman underwent neurosurgery. These events took place in the first half of the last century and marked the beginnings of the study of the human brain. They were even more special because they brought the pretense that, literally, we were about to touch the human mind.
Who operated on the teenager was the illustrious Wilder Penfield (1891–1976). He opened the skulls of his patients while awake, and in that way he had the opportunity to see what happened when he stimulated brain regions. Following this expedient, he had mapped brain areas responsible for executing the movements and others occupied in bringing us touch and pain.
Penfield noticed a scar on the girl’s right temporal lobe, probably the cause of the epilepsy. Investigatively, the neurosurgeon made stimuli around that wound. Immediately his patient started saying, “I see something coming at me, don’t let them get close.” Terrified, the girl heard hostile sounds.
The young woman’s unpleasant experience did not occur if the electrodes stimulated other parts of the brain. Thus, the doctor referred to that brain portion as the repository of memories. But her stimuli rekindled more than memories. They brought up emotions that accompanied the original experience, reasoning about the meaning of the event, plus the individual’s own interpretation of the event.
The integrated whole was more than factual recollections, but rather evoked memories, the resumption of thoughts that originated in that situation, together with the emotions that colored them. Penfield then called the study of these phenomena “the beginning of a physiology of mind.”
From that point on, he pinned his hopes on finding a way to find the brain regions that housed the mind. Just as he had mapped the brain bases for limb movements, he would find the anatomical sites that would unify consciousness, memory and the ability to experience.
When we witness an event, a chain of neuron connections forms. We will remember the event, relive emotions and reason again, always making these connections active. This is the concept of the engram: a permanent pathway made up of many synapses formed in response to an individual experience. Penfield went on to study the electrical properties of engrams.
But until today we do not have the full understanding of the engram. We haven’t even met one of them yet, in its entirety. Much less do we master the chemical phenomena that make it work and update itself. Therefore, we do not know what changes occur in neurons for memories to consolidate and disappear. Nor, how do they change as we relive our past and reinterpret past events.
Penfield was a pioneer in demonstrating that the brain has integrative centers, connecting memories to judgments and emotions. The engram is likely to be the fundamental structure for these joins.
Probably, the neurosurgeon thought that if he mapped the engrams, he would read the mind, making it accessible to his understanding and touch. It would confirm that our experience of being depends on how our attention retrieves our memories. However, Penfield did not have this success in locating the mind in the brain, despite great successes, marked by new neurosurgical techniques and the understanding of some mechanisms of brain function.
After all, we are more complex, we have characteristics that influence our mind, such as creativity, optimism, humor. Sometimes we are nostalgic, sometimes we try to distance ourselves from the past. Our mind is not in one part of our brain, it occupies all of its parts, and expands to be located throughout our body. Our body as a whole is more complex than our brain.
References:
1. Leblanc R. Pavlov, Penfield, and the physiology of the mind. Neurology. 2019 Mar 19;92(12):575–8.
2. Leblanc R. The White Paper: Wilder Penfield, the Stream of Consciousness, and the Physiology of Mind. J Hist Neurosci. 2019 Oct 2;28(4):416–36.
3. Tonegawa S, Liu X, Ramirez S, Redondo R. Memory Engram Cells Have Come of Age. Neuron. 2015 Sep 2;87(5):918–31.
4. Denny CA, Lebois E, Ramirez S. From Engrams to Pathologies of the Brain. Front Neural Circuits. 2017;11:23.
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