E.5.5 The pupil reflex
The fMRI shows areas of the brain which have increased blood flow.
Increased blood flow is associated with increased neurone activity.
When presented with a stimulus the fMRI is taken and the region of the brain with increased blood flow is linked to with the processing of that stimulus information.
In the image to the left the person has acquired Turkish and English as an early Bilingual.
When speaking each language in turn the same area of the brain experienced increased blood flow.
This area of the brain is called Broca’s area.
At this level of resolution the conclusion is that the same region processes information about both languages.
In the image to the left the experiment was repeated but this time by an individual who acquired two languages as a ‘late bilingual’.
Two different parts of Broca’s regions experienced increased blood flow.
The conclusion which might be drawn is that:The regions of increased blood flow are the same regions of the brain active during the activities.
The conclusion will be that for the late bilingual each language uses a different part of Broca’s area.
Note that this tells us nothing about language ability in either early or late bilinguals.
There is no evidence above to suggest that either organisation of the brain is better than the other. In deed at this resolution the fMRI tell us little about the actual interactions of neurones at the synapse.
The problem of limited resolution: Imagine flying late at night over a busy city, the lights below appear to be concentrated in regions of greatest activity but this tells nothing about the functioning of the city, how business is managed or how institutions are organised. So it is with fMRI that we must be careful not to over interpret the images. The resolution of fMRI is still limited so that an active region of the scan may be associated with millions of neurones. Research is developing technology that might scan the brain with greater resolution in the future.
As is often the case in medicine improved understanding of normal function often comes from the study of disease or injury. Study of when things go wrong often provides insight into normal function. Lesions of brain result in a loss or alternation of behaviour linked to the region of the brain affected by the lesion.
Example: Phuneas Cage 1848
Was working on a construction when an explosion sent a long metal rod through his skull penetrating near the eye and exiting through the roof of the skull. Phineas did not die, but the rod had passed through the frontal lobes of the cerebral cortex. Whilst he survived the accident his personality was altered and his ability to interact socially was impaired. This is an extreme example
For more detailed information on the control of heart rate see section H.5.3
Heart rate is controlled by the autonomic system which is also divided into two parts, the sympathetic and parasympathetic nervous system.
The iris reflex is under the control of the autonomic system.
If light is particularly bright the receptors cells of the retina can be come over stimulated.
To prevent over stimulation the iris is able to reduce the amount of light entering through the constriction of the pupil that as much light as possible reaches the retina the pupil dilates.
The mechanisms in the eye is based on two sets of muscles, the circular and radial muscles.
This antagonistic pair of muscles makes up the iris
Descriptions of death at the biological level:
To determine if the brain is still functional stimuli are presented such as shining light into the eye and looking for the associated pupil reflex. A reflex would indicate some function at the basic brain level of the medulla oblongata.
In the event of death cardiac output and ventilation can be maintained artificially. Some people may have decided to donate their organs for transplant but if organs are harvested it would be necessary to establish that the person was no longer capable of any brain function that would be associated with the concept of the person being 'living'.
Absence of the pupil reflex indicates no basic brain function and allow surgeons to progress towards harvesting organs.
Much of this issue depends on ones definition of 'living' and on local and national laws.
When a pain receptor in the skin is stimulated impulses are transmitted to the central nervous system to the sensory areas of the cerebral cortex.
The pituitary secretes Endorphins into the blood stream and the hypothalamus secretes them into the brain to block the receptor molecules at synapses. In doing so the pain is reduced.
An awareness of pain allows one to avoid acute injury being aggravated into chronic injury.
An awareness of pain allows one to avoid noxious substances.
Perception of pain is also used in aspect of social organisation e.g lion cubs mock fighting
Having the perception of pain has a distinct survival benefit however there comes a point at which the pain needs to be blocked.
E.5.5 The pupil reflex