12.2 Applications and skills

12.2.2 Specialisation of brain function

On this page we look at examples of specialisation in brain function, and find out a bit more about how knowledge of these functions was obtained.

The visual cortex, Broca’s area and nucleus accumbens

Figure 12.2.2a – CerebrumFigure 12.2.2a – Cerebrum
Functional locations of the cerebral cortex in the left hemisphere (left) and right hemisphere (right)

Structure

Location

Function

Visual cortex

Occipital lobe, left and right hemispheres

Processing visual information

Broca’s area

Frontal lobe, left hemisphere only

Speech production, and writing

Nucleus accumbens

Basal forebrain – in front of the thalamus, left and right hemispheres

Involved in motivation, pleasure, reward and re-inforcement learning

 

The medulla oblongata coordinates swallowing, breathing and heart rate

  • All nervous impulses travel through the medulla on their way to and from the brain.
  • The medulla oblongata contains clusters of cells, or nuclei, which regulate the rate of respiration and the heart rate, as well as reflex actions such as swallowing (and vomiting).

Respiratory centre

Chemoreceptors respond to changes in blood pH

Signals the diaphragm and intercostal muscles to increase breathing rate

Cardiac centre

Connected to vagus nerve and cardiac accelerator nerve

Activation of vagus nerve slows heart rate

Activation of accelerator increases heart rate

Reflex centre

Initiated by the cerebral cortex (the first part of swallowing is conscious)

The medulla coordinates the contraction of smooth muscles in the esophagus

 

Brain damage can be evaluated using the pupil reflex

  • The pupil reflex is an autonomic function coordinated by the brain stem.
  • Shining a bright light into the pupil stimulates the visual cortex through the optic nerve, which then signals the parasympathetic nervous system to contract the circular muscles in the irises of both eyes.
  • The pupil constricts, preventing bright light from damaging the retina.
  • Failure of the pupil to respond appropriately to the light indicates damage in the brain.

Figure 12.2.2b – Pupil reflex test

Figure 12.2.2b – Abnormal response to the pupil reflex test indicates damage to the brain.

  • Brain death is medically defined as the permanent absence of measurable activity in the brain.
  • The pupil reflex is one of the criteria used to determine brain death because if the pupils do not respond at all, it indicates damage in the medulla oblongata, which regulates all autonomic functions and homeostasis (including breathing).
  • A patient who is brain dead will probably not recover but can be kept alive in a vegetative state (i.e. on life support).

Determining the role of brain parts through fMRI, animal experimentation, autopsy and lesions

Functional magnetic resonance imaging (fMRI)

  • This modern technique maps changes in blood flow to different parts of the brain, indicating regions of brain activity while different tasks are performed.
  • Since oxyhemoglobin and hemoglobin respond differently to the magnetic field in the machine, fMRI uses blood-oxygen-level-dependent (BOLD) contrast to calculate brain activity.

12.2.2cFigure 12.2.2c – fMRI
fMRI scans show changes in blood oxygen levels as different colours.

  • When there is a change in blood oxygen level due to cellular respiration, there is a corresponding colour change in the image.

Animal experimentation

  • Electroencephalography (EEG) records electrical activity through sensors placed on the skull. It can be used on animals or humans in conjunction with fMRI.
  • To monitor electrical activity in specific cells, animals are sometimes fitted with microelectrodes that penetrate the brain. This would not be allowed in human subjects.

12.2.2dFigure 12.2.2d – Microelectrodes for EEG

  • Good animal models include mice and ferrets – mammals that have a developed cerebral cortex. They are selectively bred for laboratory use.
  • People object to the use of animals in neurobiological research because it sometimes involves harm or death to the animals.
  • There are very strict guidelines and codes of ethics involved in the use of animals for research.

Autopsy and lesions

  • Direct information can be obtained by opportunistically studying human patients who have suffered from brain damage, lesions and strokes.
  • Lesions in one part of the brain result in specific changes. For example, lesions in the frontal lobe result in personality shifts such as increased aggression and risk-taking behaviour.

12.2.2eFigure 12.2.2e – EEG
Children with Angelman syndrome, a severe neuro-genetic disorder, display a characteristic EEG profile. EEGs can also be used to detect early signs of autism in children.

TOK

In medicine, the concept of death is defined in terms of brain function, but sometimes conflicts can occur when the medical criteria for death differ from a family’s criteria for death. To what extent should the views of family members be given priority when making decisions in medical ethics? Which criteria should be used to make ethical decisions?

12.2.2fFigure 12.2.2f – Mouse
In 2014, the Nobel Prize for physiology/medicine was awarded to three researchers who discovered cells in the hippocampus that play a role in orientation and navigation (called ‘place’ and ‘grid’ cells). Their work started in 1971 and relied on animal experimentation.

Course link

  • Review how nervous input controls the heartbeat in 6.1.2.
  • More information on the effect of pH on respiration rate can be found in 15.1.6.