femme Neuroscience Notes

Some Topics


In the popular imagination, a brain surgeon is among the smartest of all humans. While there is no doubt that neurosurgeons are special people with rare skills, a brain surgeon needs to practical, patient, methodical and precise more than he needs to be a brilliant intellectual. The surgeon who spends 5 hours meticulously exposing the blood vessels on the brain stem so that he can put a clip on an aneurysm is a model of patience and precise movement. His goal is a rather simple task (clipping an aneurysm), but getting to the aneurysm without doing damage is slow and difficult. He is working in a small, dark space using a microscope and special lighting to find his way. Every movement is planned and critical. A small error in finger motion can leave the patient disabled.

Neurosurgeons are practical people who look after, for example, patients with head and neck injuries. The consequences of these injuries are often devastating. The best surgical technique and intensive care may have little or no benefit in the end, so that neurosurgeons have to be unusually dedicated and accepting of their limitations. All neurosurgeons have a sense of modular function in the brain and approximate how a functioning person is composed of these modules. In the day-to-day care of patients and during operations, you have to a have a sense of what functions reside in what part of the brain and how important each function is. Some areas of the brain are more critical than others. You can get away with damaging or removing some parts of the cerebral cortex, for example, but you cannot damage the motor cortex without causing paralysis, deficits that are obvious to all.

The question of who recovers from a head injury or surgery to remove a brain tumor is both a practical matter of neuroanatomy and surgical experience and judgment and a deep philosophical matter. Families of neurosurgical patients often recognize that there is a connection between the brain and mind, but become confused about who does what to whom when brain injury is severe. A patient with a head injury from a car accident with damage to both the frontal lobes may awaken from a coma after the brain swelling subsides and everyone is delighted that the patient survived such a severe injury.

The person who walks out the hospital, however, is not the same person who hit his head on the windshield of the car. The initial celebration of recovery may turn to confusion and despair as the consequences of frontal lobe damage become apparent in subsequent years. Frontal lobe dysfunction is both fascinating and horrifying since, the most advanced and most subtle functions of the human mind reside there.

A blow to the frontal lobes can kill neurons and interrupt systems that are essential for motivation, planning, empathy and appropriate behavior. Paralysis is easy to recognize but changes in character, judgment and cognitive abilities are not so easy to recognize. If damage occurs to the speech centers in the temporal and frontal lobes, deficits are obvious to all observers. Damage to the brain stem is catastrophic.

Some of the evidence for the brain-mind connection comes from neurosurgery.  Two obvious contributions of neurosurgeons that have entered the common understanding of bodymindbrain are the cortical stimulation maps produced by Canadian neurosurgeon, Wilder Penfield and the split-brain patients done by American surgeon, Roger Sperry and his colleagues. Penfield demonstrated localized functions on the surface of the cortex and also revealed “silent areas.” The presence of silent areas led to the incorrect but still-popular idea that humans only use 10% of their brain. Sperry’s operations led to ideas of right and left hemispheric specialization.

Extravagant speculations followed, based on doubtful attributions of right and left brain function in normal people. Sperry separated the two cerebral hemispheres by cutting the corpus callosum, isolating each hemisphere. The result was described as a “split-brain” patient. The patients are unaware that they have changed. Their family and friends may be unaware of any changes in personality or cognition. With close study of specific cognitive functions, these split-brain patients appear to have two separate domains of consciousness with no insight into their altered states.

Neurosurgeons are concerned with loss of consciousness since brain injury and tumor growth is often associated with deteriorating consciousness and coma. The evaluation of a comatose patient is a specialized process that starts with careful examination of the patient and now depends on diagnostic machines such as CAT scan and MRI that makes detailed images of the brain and other tests that evaluate blood flow. An EEG machine records the electrical activity of the brain and can be used to diagnose brain death if there is no electrical activity on repeated examination.

The care of brain-damaged patients is centered on monitoring and attempting to control the pressure inside the head. The skull is an unyielding, hard container and the brain is soft like jelly. If the intracranial pressure rises, the brain is compressed and soft critical areas such as the brain stem can be compressed enough to stop working. The brain stem contains vital neuron clusters that control breathing and heart function. Compressing these vital centers leads to death.

The blood supply to the brain is another major concern of surgeons. Four arteries supply the circulation to the brain. The two larger arteries in the front of the neck (internal carotid arteries) connect with the two smaller arteries in the rear (vertebral arteries) form a circular distribution system (circle of Willis) that lies on the front of the midbrain. The most common brain injury is damage done by obstructed blood flow (ischemia) in this arterial system. Ischemic brain damage is called a stroke and the most common stroke involves the middle cerebral artery that supplies blood flow to the motor cortex and speech centers in the brain. The stroke victim is often paralyzed on one side. Loss of language ability is associated if the damage is to the left cerebral cortex in 92% of all patients (who are right handed.)

Some neurosurgeons have become cognitive scientists and philosophers who explored the brain basis of mind.  I encountered Neurosurgeon-philosopher, Benno Schlesinger’s book “Higher Cerebral Functions’   when I was a medical student working in a mental hospital.  This was a revolutionary text for me. Schlesinger attempted to integrate a practical and clinical point of view with speculations about how the brain really works and why geniuses are so smart. Schlesinger would state for example:” Affectivity is a manifestation of high level autonomic function; thought is intra-sensory integration at the highest level and skill is sensory-motor integration at the psycho-neural level.” He created schematic models of cognitive function based on 3 levels of sensory and motor processing. He considered sensory level 1 to be perceptual or raw data coming in. Level 2S was configurations and level 3S was concepts and ideation. Motor output was processed in a similar manner at three levels of integration. While there is little doubt that the brain is modular and that information processing occurs in a progressive or sequential manner at different levels of integration, the three level concepts has been replaced by a more complex and flexible sense of how the brain might be working. For example, I will argue that perception and cognition are not separate sensory levels 1 and 3, but are integrated at every level of processing. The question of where and when sensory information appears as a monitor image in consciousness cannot be decided by any available means.