Topic E5: The Human Brain

Structure:

You need to be able to label this diagram:

Functions of the labeled parts:

Medulla oblongata: controls automatic and homeostatic activities, such as swallowing, digestion and vomiting, and breathing and heart activity.

Cerebellum: coordinates unconscious functions, such as movement and balance.

Hypothalamus: maintains homeostasis, coordinating the nervous and endocrine systems, secreting hormones of the posterior pituitary, and releasing factors regulating the anterior pituitary.

Pituitary gland: the posterior lobe stores and releases hormones produced by the hypothalamus and the anterior lobe. It produces and secretes hormones regulating many body functions.

Cerebral hemispheres: act as the integrating centre for high complex functions such as learning, memory and emotions.


Explain how animal experiments, lesions and FMRI (functional magnetic resonance imaging) scanning can be used in the identification of the brain part involved in specific functions. Read below and find one example of each that interests you (delete the rest) and learn it!

Beginning with the pioneering experiments of Flourens, around 1825, the first discoveries related to this question came only when he and other anatomists and physiologists developed new experimental methods to intervene directly into the brain, and to see the results of these interventions on the behavior of animals. These methods were:

1.  Selective surgical removal (lesions) of parts of the brain of animals;

2.  Faradic and galvanic (i.e., steady or pulsed electrical) stimulation of the brain of animals and humans;

3.  Clinical studies, i.e., patients with neurological or mental deficits had their brain studied after their death, in an attempt to correlate them with detectable alterations in the brain tissue.

Flourens started by using localized lesions (cutting out) of the brain in rabbits and pigeons. He was able to demonstrate convincingly for the first time that the main divisions of the brain were responsible for largely different functions. By removing the cerebral hemispheres, for instance, all perceptions, motor operations, and judgment were abolished. The removal of the cerebellum affected the animal's equilibrium and motor coordination, while the destruction of the brain stem (medulla oblongata) caused death. These experiments led to the conclusion that the cerebral hemispheres are responsible for higher cognitive functions, that the cerebellum regulates and integrates movements, and that the medulla controls vital functions, such as circulation, respiration and general bodily stability. On the other hand, he was unable (probably because his experimental subjects have relatively primitive cortices) to find specific regions for memory and cognition, which led him to believe that they are represented in a diffuse form around the brain. So, different functions could indeed be ascribed to particular regions of the brain, but that a finer localization was lacking. / Pierre Flourens


A pigeon which had its brain lesioned in an experiment by Flourens

For the next 30 years, this was the predominant view, until a series of clinical discoveries in France and Germany, related to the pathology of language, provided a clue that higher mental functions had, indeed, a specific localization in the cortex. In addition, new experiments with more precise electrical stimulation of the cortex surface in primates and dogs, in England and Germany, provided a stronger case for strict localization of function.

The clinical approach was pioneered by the French physician Pierre Paul Broca. In a classical work, carried out around 1860, he studied the brain of several aphasic patients (that is, they could not talk; one of them, who became the most famous, in fact was able to utter just one word: tan). After his death, Broca discovered that Tan's brain had a relatively small zone destroyed by neurosyphillis, which was delimited to one side of the anterior brain hemispheres (cortex). This part of the brain later became known as Broca's area, and it is responsible for the control of speech (motor expression of the language). His studies were confirmed by several neurologists, including John Hughlings Jackson, the doyen of British neurologists, who was able to confirm the laterality of function in aphasic patients, and to provide a major conceptual integration of functional localization in the brain, by means of his "hierarchical" theory. This was based on the observation that higher functions such as thought and memory, were less affected by lesions than lower ones, such as the control of respiration and circulation.
More or less at the same time, a German neurologist, Carl Wernicke, discovered a similar area in the temporal lobe, which, when lesioned, led to sensory deficit in language, i.e., the patient was unable to recognize words, although he or she could hear sounds quite well. Wernicke thought that his area (which was named after him) was connected by fiber systems to Broca's area, thus forming a complex system responsible for understanding and talking.
Later on, around the same time as Broca and Wernicke (1870), two German physiologists, Gustav Fritsch and Eduard Hitzig, improved our knowledge about brain localization of function, by stimulating with electricity small regions exposed on the brain's surfaces of awake dogs. They discovered that the stimulation of some areas caused muscle contractions in the head and neck, while the stimulation of distinct brain areas caused contractions of the forelegs or hind legs, thus providing the first evidence for a finer localization of function in the cortex, and starting a whole new paradigm for mapping the brain.
A neurosurgeon named Feodor Krause went even to the extreme length of stimulating the cortical convolutions of anesthetized patients who were being submitted to brain surgery for the removal of tumors. His mapping of the motor areas of the cortex were remarkably accurate, and provided a background for more modern investigations in patients with local anesthesia, such as the experiments carried out by Wilder Penfield in the 40s and 50s.
The work of Fritsch and Hitzig was considerably extended, with a tremendous impact on our knowledge of the brain, by a series of elegant experiments on dogs and monkeys by Sir David Ferrier, a British neurologist and physiologist. Between 1870 and 1875 he stimulated with electricity the cortical gyri of these animals and was able to detect 15 different areas related to the precise control of movement. Later on, he removed surgically the same spots where some movement was elicited and was able to demonstrate the abolition of the corresponding motor function.
Ferrier boldly predicted, with a good accuracy, how these points could be translated to a human's brain, and used this knowledge successfully, for the first time, to orient neurological diagnosis and the operation of the brain of patients of tumors. For instance, he correctly predicted the localization of a cortical lesion in a patient with paralysis in the fingers and forearm at one side and provided a clue to Macewen, a surgeon, to remove the tumor with greater accuracy.
Ferrier views were in stark opposition to Flouren's regarding cortical localization, as well as to other researchers in his time, such as Friedrich Goltz, who was unable to abolish localized functions in dogs even when he carried out extensive hemispheric lesions. This led to a famous public dispute between Goltz and Ferrier, which was won by Ferrier, mostly because he was able to demonstrate that Goltz's surgical lesions did spare some motor and sensory cortex, at the same time dogs being less dependent on cortical functions than primates. /
Pierre Paul Broca

Carl Wernicke

Feodor Krause

Gustav Fritsch and Eduard Hitzig

Sir David Ferrier

Frie drich Goltz
Monkey cortex with stimulation points by Ferrier

http://www.cerebromente.org.br/n01/frenolog/frenloc.htm

Functional MRI or functional Magnetic Resonance Imaging (fMRI) is a type of specialized MRI scan. It measures the blood flow response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neural imaging. Since the early 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.

Subjects participating in a fMRI experiment are asked to lie still and are usually restrained with soft pads to prevent small motions from disturbing measurements. Some labs also employ bite bars to reduce motion, although these are unpopular as they can cause some discomfort to subjects. It is possible to correct for some amount of head movement with post-processing of the data, but large transient motion can render these attempts futile. Generally motion in excess of 3 millimeters will result in unusable data. The issue of motion is present for all populations, but most notably within populations that are not physically or emotionally equipped for even short MRI sessions (e.g., those with Alzheimer's Disease or schizophrenia, or young children). In these populations, various and negative reinforcement strategies can be employed in an attempt to attenuate motion artifacts, but in general the solution lies in designing a paradigm compatible with these populations.

An fMRI experiment usually lasts between 15 minutes and 2 hours. Depending on the purpose of study, subjects may view movies, hear sounds, smell odors, perform cognitive tasks such as n-back, memorization or imagination, press a few buttons, or perform other tasks. Researchers are required to give detailed instructions and descriptions of the experiment plan to each subject, who must sign a consent form before the experiment.

Safety is a very important issue in all experiments involving MRI. Potential subjects must ensure that they are able to enter the MRI environment. Due to the nature of the MRI scanner, there is an extremely strong magnetic field surrounding the MRI scanner (at least 1.5 teslas, possibly stronger). Potential subjects must be thoroughly examined for any ferromagnetic objects (e.g. watches, glasses, hair pins, pacemakers, bone plates and screws, etc.) before entering the scanning environment.


Comparison of sympathetic and Parasympathetic nervous systems

Look at this animation:

http://itc.gsw.edu/faculty/gfisk/anim/autonomicns.swf

Parasympathetic nervous system prepares the body for Pleasure. The Sympathetic nervous system reacts to a Scare!

Think

Why should Eyes dilate? Maximize light entering the eye to maximize information about a threat. Why should blood flow to the guts reduce? Which is more important running away from a threat or digesting food? Why might blood flow be needed more in times of fight or flight? Where might more blood flow be needed in times of fight or flight?

Pupil reflex

Description:

The pupillary light reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye. Greater intensity light causes the pupil to become smaller (allowing less light in), whereas lower intensity light causes the pupil to become larger (allowing more light in). Thus, the pupillary light reflex regulates the intensity of light entering the eye.

Look at this animation of the reflex arc for the Pupil.

http://library.med.utah.edu/kw/hyperbrain/anim/reflex.html

Clinical significance

In addition to controlling the amount of light that enters the eye, the pupillary light reflex provides a useful diagnostic tool. It allows a physician or opthamologist to test the integrity of the sensory and motor functions of the eye.[1]

Emergency room physicians routinely assess the pupillary reflex because it is useful for gauging brain stem function. Normally, pupils react (i.e. constrict) equally. Lack of the pupillary reflex or an abnormal pupillary reflex can be caused by optic nerve damage, oculomotor nerve damage, brain stem death (look below) and depressant drugs, such as barbiturates.

Normally, both pupils should constrict with light shone into either eye alone.

http://en.wikipedia.org/wiki/Pupillary_light_reflex

Brain Death

Two definitions:

Brain stem death is the UK version of brain death. It was first formally introduced in 1976 and has been ratified by the Department of Health and Medical Royal Colleges on several occasions since, most recently in October 2008. Its equation with human death is based on the concept that when essential elements of the brain stem - the stalk of the brain which connects its bulk (the cerebral hemispheres and mid-brain) to the spinal cord - are permanently out of action it is reasonable to disregard continuing activity (life) elsewhere in the brain, e.g. in the thalamus and "higher centres", because there can never again be consciousness or spontaneous breathing (Academy of Medical Royal Colleges: 'A Code of Practice for the Diagnosis and Confirmation of Death', October 2008). That concept has not found acceptance in the USA where the irreversible cessation of all functions of the entire brain ("total brain failure") must be certainly established for the diagnosis of death on neurological grounds. That position has been re-emphasized in the recently published White Paper on 'Controversies in the Determination of Death' by the President's Council on Bioethics, which describes reliance on the reductionist "brain stem death" criterion for the declaration of death as "conceptually suspect" and "clinically dangerous".

Pain Perception and Endorphins

Limit this to:

• passage of impulses from pain receptors in the skin and other parts of the body to sensory areas of the cerebral cortex

• feelings of pain due to these areas of the cerebral cortex

• endorphins block transmission of impulses at synapses involved in pain perception.