Split Brain Research
Hemispheric lateralisation: This is the ideas that the brain’s two hemispheres are responsible for different functions; that particular functions (such as language) are the responsibility of one hemisphere but not the other- the function is lateralised.
Split-brain research: This involves individuals who have had surgical separation of their brain hemispheres, in order to relieve symptoms of epilepsy. Research can reveal to what extent other brain functions are lateralised. Sperry (1968) used a procedure where an image or word was projected to the patient’s right visual field (which would be processed by the left hemisphere) and another image was projected to the left visual field (processed by the right hemisphere). In a split-brain patient, information cannot be transmitted from one hemisphere to another, so the effects of this can be studied.
Findings from split-brain research: When a picture was shown to the right visual field, the patient could describe it easily. When the image was shown to the left visual field, the patient found it difficult to describe it, or couldn’t see anything there. This is likely due to the lack of language processing ability in the right hemisphere, which processes the left visual field. The left hemisphere was unable to receive the information due to the separation of the hemispheres.
When patients were presented with a word or object in the left visual field, then had to select that object (or a related one) from a bag using their left hand without looking, they were able to do this quite well. This is despite the fact that they couldn’t describe what the object was. They could still seemingly understand what the object was, showing that the right hemisphere is involved in understanding of objects.
When patients were presented with two words simultaneously (for example, ‘door’ ‘frame’), one in each visual field, they wrote the word in the left visual field (‘door’) with their left hand, and said the word in the right visual field (‘frame’). The left hand was much better at drawing images than the right hand, despite the fact that all of the patients tested were right-handed. This shows that the right hemisphere seems to be dominant for drawing skills.
When asked to match a face from a number of other faces, the picture presented to the left visual field (processed by the right hemisphere) was consistently selected, whilst the image presented to the right visual field (left hemisphere) was ignored. This shows that the right hemisphere seems dominant in face recognition. Images presented as composites of two faces led to the left hemisphere dominating when the patient was asked to verbally describe the face (the right-hand ‘half’ of the face was described, and the left-hand half ignored), and the right hemisphere dominated when the patient had to select a matching face from a number of others.
- Sperry’s research supports the conclusion that the left hemisphere is more responsible for verbal and analytical tasks, whereas the right hemisphere is better at spatial and musical tasks. This has strengthened the understanding of how the brain works.
- Sperry’s procedure was closely controlled. Patients were given eye patches, and images were flashed up for a very brief time (fractions of a second), meaning there was no possibility of looking over and using the other visual field. This strengthens the internal validity of the studies.
- The sample used by Sperry was quite small (only 11 took part in all procedures), and their brains may have been affected by epileptic seizures. Therefore, it is hard to generalise the findings from the studies to the general population.
- Functional magnetic resonance imaging (fMRI): this measures changes in blood flow and oxygenation in the brain whilst the individual is performing a task. Increased blood flow suggests that the area of the brain is working harder, so it can be determined which areas of the brain are involved with particular tasks.
- Electroencephalogram (EEG): measures the electrical activity of neurons in the brain, by recording the electrical impulses that take place during synaptic transmission. The individual wears a skull cap to do this. This can detect particular patterns of activity in the brain, for example what is happening during sleep.
- Event-related potentials (ERPs): activity from an EEG recording is analysed, in order to determine the specific responses relating to a particular task. Event-related potentials are therefore the results of this- types of brainwave which are triggered by particular events.
- Post-mortem examinations: the brain is studied and analysed following death, by looking at particular areas. This is often done for individuals who have had rare disorders or dysfunction in behaviour or cognitions. Their brain will be compared to a ‘control’ brain to see if there are differences in structure.
- fMRI is low-risk, involving no radiation, and produces very detailed images. However, it is expensive, and there is a time-lag- the image taken is 5 seconds behind the initial firing of neurons (therefore, this is poor temporal resolution). Also, the activity of individual neurons cannot be seen.
- EEGs have been very useful in diagnosing conditions such as epilepsy, and the processes involved in activities such as sleep. Brain activity can be measured almost instantaneously (a single millisecond), unlike in fMRI. However, the information gained is very generalised, so the technique can’t be used to isolate exact neural activity.
- ERPs draw on EEGs to measure more specific activity in the brain. They have excellent temporal resolution and are widely used in identifying specific behaviours and functions. Many different ERPs have been successfully identified. However, there is a lack of standardisation in the methodology used, meaning the findings are in question, and eliminating all extraneous variables in order to isolate an ERP can be difficult.
- Post-mortems have greatly enhanced medical knowledge, for example Broca and Wernicke both made use of them before neuroimaging techniques were possible. However, it is hard to establish a cause-effect link when conducting post-mortem studies. Changes in brain structure may not be related to the disorder the patient had, but due to another issue.
A biological rhythm is a change in the boy’s processes, in response to environmental changes. These rhythms are influenced by external and internal factors. The internal factors are the body’s internal processes- the ‘body clock’, known as endogenous pacemakers. External factors are changes in the environment, known as exogenous zeitgebers. Rhythms that last around 24 hours are known as circadian rhythms.
Sleep/wake cycle: This is an example of a circadian rhythm. The exogenous zeitgeber in this case is the daylight (or lack of it), which contributes to feelings of drowsiness or being awake. Researcher Michael Siffre studied the effect of a complete lack of daylight on his own sleep/wake cycle, by living in a cave for several months at a time. After two months in one cave, he emerged believing the date to be mid-August, but it was actually mid-September. In each experiment, his body created a natural rhythm of just beyond the usual 24 hours, and he continued to sleep and wake on a regular cycle.
Aschoff and Wever (1976) found that participants who spent 4 weeks in a bunker without natural light showed circadian rhythms of 24-25 hours, except one participant who went up to 29 hours. This suggests the natural circadian rhythm is slightly shortened by the effects of daylight. Folkard et al (1985) found that when participants were deprived of sunlight for 3 weeks, and the length of day was manipulated by the researchers to 22 hours rather than 24 (by covertly adjusting the time on the clocks), only one participant easily adjusted to the shortened day. This suggests the strength of the body’s sleep/wake cycle, as it resisted environmental changes.
- Research into circadian rhythms has useful practical applications, for example how to manage the shift patterns of night workers so that they are more productive and make fewer mistakes. This increases the usefulness of the studies.
- Research has also shown when the effects of drugs on the body are at their most and least effective. Circadian rhythms seem to have an impact on how drugs affect the body, so guidelines can be developed for patients as to when they should take drugs for maximum impact. This is another useful practical application.
- Research in this area often uses small sample sizes (only 1, in the case of Siffre), so generalisation may be difficult. Also, participants had access to artificial light, which could have acted as a confounding variable- for example, turning off a light to go to sleep may have similar effects as the end of natural light at the end of a day. The internal validity of the research is therefore in question.
Infradian & Ultradian Rhythms
These take place over a longer time than 24 hours. For example, the menstrual cycle. This takes place over around 28 days, although this varies between women. Hormone levels rise during the cycle, which causes the release of an egg (ovulation), then the release of the hormone progesterone which thickens the womb lining to ready the body for pregnancy. If no pregnancy occurs, the womb lining comes away, resulting in menstruation.
There is evidence that the menstrual cycle can be affected by exogenous factors. McClintock et al (1998) found that collecting pheromones (chemicals released into the air and absorbed by others, affecting their behaviour) from women with irregular cycles and rubbing them on the lips of other women caused the ‘receiver’ of the pheromones to experience changes in their cycle, bringing them closer to the pheromone ‘donor’.
Seasonal affective disorder (SAD) is another infradian rhythm, characterised by changes to mood. Sufferers feel a lowered mood, and lowered activity levels, during the winter months when daylight is shorter. As their mood changes in a predictable way through the year, this is an example of a circannual rhythm. This is thought to be caused by the hormone melatonin, which has an effect on serotonin, a neurotransmitter linked with depression. More melatonin is released during the winter, as it is released when there is a lack of daylight.
These take place more than once within a 24-hour period. An example is the different stages of sleep, of which 5 distinct stages have been identified through research involving an EEG.
- Stages 1 and 2: a light sleep, where a person can be easily woken. Brain wave patterns start to slow down, becoming more ‘rhythmic’ (alpha waves) at this time.
- Stages 3 and 4: delta waves take over, which are even slower than alpha waves. This is a deep sleep; from which it is hard to wave the person- sometimes known as ’slow wave sleep’.
- Stage 5: the pons (part of the brain) paralyses the body to stop the person from ‘acting out’ their dreams. The eyelids move in a fast, jerky fashion at this point, which is correlated with dreaming. Therefore, this stage is known as REM sleep (rapid eye movement).
- Research into the menstrual cycle is likely to be affected by many variables, such as diet, stress, amount of exercise, and so on. This means that the findings of studies such as McClintock may not be valid. Other studies have found no evidence of menstrual synchrony (women’s cycles moving closer to each other’s).
- Dement and Kleitman (1957) found that REM activity was strongly correlated with dreaming. Participants woken during REM sleep were able to describe dreams in vivid detail. This supports the effect of biological rhythms on the body and brain.
- An effective treatment for SAD has been developed as a result of research in this area. Sufferers are given a light box to simulate the effects of sunlight in the dark mornings and evenings of winter, which has led to a relief in symptoms for around 60% of sufferers. This increases the practical usefulness of research into infradian rhythms.
The suprachiasmatic nucleus (SCN): This is located in the brain’s hypothalamus in both hemispheres, and is influential in the maintenance of circadian rhythms. The SCN receives information about light from a structure called the optic chiasm, which sends messages from the eye to the visual area of the cerebral cortex. This can continue even if the person’s eyes are closed, allowing the body to adjust to changing daylight patterns.
Animal studies involving the SCN have shown that if the SCN connections are destroyed, the animals no longer have a sleep/wake cycle- this was observed in chipmunks by DeCoursey et al (2000). In addition, Ralph et al (1990) found that hamsters who received SCN cells through transplant from other hamsters bred to have a 20-hour sleep/wake cycle themselves defaulted to a 20-hour sleep/wake cycle.
The pineal gland and melatonin: The SCN passes information about daylight to the pineal gland, which is located behind the hypothalamus. This gland increases melatonin production, which induces sleep and is inhibited when a person is awake. As previously seen, melatonin is a possible cause of seasonal affective disorder.
Environmental factors have an influence on biological rhythms through a process known as ‘entrainment’. These factors work with the body’s internal processes to affect rhythms such as the sleep/wake cycle.
Light: This resets the SCN, so has a key effect on the sleep/wake cycle. Hormone production and other processes are also influenced by light. Campbell and Murphy (1998) found that skin can detect light- when participants had light shone on to the back of their knees, this affected the duration of their sleep/wake cycles- even if it was dark outside. This suggests that light is perceived not just by the eyes, and has an effect on the body.
Social cues: Infants have no set sleep/wake cycle until about 6 weeks of age, and this process generally continues until around 16 weeks, when babies are entrained. This could be due to the schedules imposed on them by parents. Similarly, the effects of jet lag can be reduced by quickly adapting to local times for sleeping and eating (not going to bed when you feel tired, for example). This suggests that the body does respond to cues in the environment.
- Damiloa et al (2000) found that other organs in the body have their own circadian rhythms in cells known as ‘peripheral oscillators’. Changing feeding patterns in mice led to changes in the rhythms of the mice’s livers, for example. This supports that there are many influences on circadian rhythms, aside from the SCN.
- Animals used in this research are often exposed to great harm, for example in the DeCoursey study many of the chipmunks were killed by predators after their sleep/wake cycle was destroyed. This raises the question of whether the research is ethically justifiable.
- Evidence suggests that exogenous zeitgebers may not actually have much of an effect on biological rhythms. Miles et al (1977) reported that a man who was blind since birth and had a sleep/wake cycle of 24.9 hours could not have his cycle adjusted by any external factors such as social cues. Instead, he had to take sedatives at night and stimulants in the morning so that he could live in the ’24-hour world’. This weakens the influence of exogenous zeitgebers on biological rhythms.
- What are the nervous system’s two sub-systems?
- Your answer should include: Central / Peripheral
- What are chemicals which travel across synapses?
- Who received extensive damage to his frontal lobe following an accident?
- Your answer should include: Phineas / Gage
- What is the ability of the brain to change and adapt as a result of learning and experience?
- What research involved epilepsy patients who had had a separation of the two hemispheres of their brain?
- Your answer should include: Split-brain / Research
- What way of investigating the brain involves measuring electrical activity using a skull cap?
- What kind of biological rhythm takes place over around 24 hours?
- Your answer should include: Circadian / Rhythm
- Who investigated the sleep/wake cycle by living in a cave for several months?
- Which condition is thought to be caused by an excess of melatonin production?
- Your answer should include: Seasonal / Affective / Disorder
- What are ‘internal body clocks’ scientifically known as?
- Your answer should include: Endogenous / Pacemakers