A Canadian neurosurgical pioneer, Sir Wilder Penfield, mapped out the areas of cerebral cortex involved in sensation and motor activity by stimulating them electrically in patients on the operating table. Brain operations can be performed under local anesthesia as the brain itself is not sensitive to touch or painful stimuli. Several times I have opened the cranium at the beginning of a brain operation during my surgical residency and found this to be true. His early sketches have been referred to as Penfield's Homunculus (= little man). "A" is a section through the sensory cortex (Parietal Lobe) and "B" is a section through the motor cortex (Frontal Lobe).
But what really fascinated this neurosurgical pioneer as long ago as the 1930s was the question: “Where is the mind?” In other words, what part or parts of the brain are involved in consciousness and the awareness of self?
The great neurologist, Herbert Jasper describes this quest in his article, The Centrencephalic System (CMA Journal June 18, 1977, pages 1371-2) and tells us Penfield concluded 40 years ago that “all regions of the brain may well be involved in normal conscious processes but the indispensible substratum of consciousness lies outside the cortex.” This greatly surprised his colleagues who felt the highest level of neuronal integration must be in the cortex, an area that is so highly developed in primates. Penfield wrote, Mysteries of the Mind, a book published by Princeton University Press in 1975 when he was 80 years of age. In it Penfield described the Centrencephalic System, stating it consists of “two units: 1) the mechanisms, the action of which is essential to the existence of consciousness: and 2) the mechanism of sensory-motor co-ordination.” This then involves also the lowly brainstem and subcortical relay centers such as the thalamus, —areas common to all vertebrates at least. Animal rights champions will find their arguments supported by this concept since even fish have a sense of who they are and can feel pain just as we do. Going further, we know that the ability to feel pain is a protective function so that we may avoid danger. Try putting a worm on a hook and you will observe that this is a very painful experience for the worm.
But what happens when we feel pain in the heart? I don't mean cardiac angina. That pain indicates a problem in the muscle pump that moves our blood around. My mother was told my father died of a broken heart. She suffered mental anguish for more than a year because she thought she had done something to hurt his feelings, when in fact he had died of a ruptured myocardium following a silent infarct. But when someone says, “I love you with all my heart,” what does that person mean?
Years ago, when heart transplantation began, many possible recipients expressed concern that the heart transplanted might have come from a murderer and that transplanting it would change the recipient’s way of thinking about people. The origin of these ideas goes back many centuries, to the time when people thought the fist-sized organ in the chest we call the heart was the seat of the emotions, and that control of emotions was its function. Now we know it is just a muscle pump. Rather than producing emotions, it can be seriously injured by bad emotions acting through the sympathetic system. Coronary blood flow can be reduced by anger and the effects of stress, with fatal results. So if the heart is not the seat of emotions, where is it?
The Limbic Lobe of the brain on the medial wall of the two cerebral hemispheres is made up of the cingulate and parahippocampal gyruses, joined together at the isthmus of the cingulate gyrus. This is called a lobe but really is part of other lobes as it lies on the medial (inner) aspects of the standard frontal, temporal and parietal lobes. Each is cross-connected by a part of the Corpus Callosum to its counterpart on the others side of the brain.
The Limbic System includes these cortical areas on each side together with the amygdala and hippocampus. It is the seat of emotions, what we used to think was the “heart.” It connects directly to the hypothalamus, through which outer expressions of emotion such as sweating, blood vessel constriction or relaxation, heart rate, gut motility, etc, are produced. Feeding into this system are smell, visual inputs, memory and thoughts. It sends out information to motor areas that influence behavior. So someone who we say has a “bad attitude” will have previously developed neuronal connections here that could lead to a socially unacceptable response in a particular situation. Such people can have their “buttons pressed” by feeding in appropriate stimuli. The same applies on the positive side, e.g., the smell of food stimulates hunger for food while hunger for sex can be aroused by stimuli that are appropriate to that individual.
It is not possible to present here the many intricate interactions involved in emotion. This part of the brain is very complex and on-going research continually sheds new light on the subject. Hopefully the above offers an introduction that will stimulate further reading. It should not be surprising to those of us with an academic interest in pain that the limbic system is involved in both acute and persistent pain, and when that pain persists, depression follows.
What is this, a part of the brain, perhaps indistinguishable from the mind? Or is the concept just a myth from days gone by? The debate has never ceased but a recently published book based on scientific evidence says, “Yes, there is a soul, and it is not where people have suggested it was.” I was asked by The Medical Post to write a review of the book The Spiritual Brain and the book review appeared in that paper April 1 2008. You can read the review here
The co-author of that book, Denyse O’Leary http://mindfulhack.blogspot.com/ has an active blog site that carries interesting information on the brain.