bio-psych

• Divisions of the Nervous System

  Central Nervous System (CNS): Involves both brain and the spinal cord. Brain is the centre of all conscious awareness. The brain's outer layer is the cerebral cortex and is highly developed in humans. Brain is divided into two hemispheres. Spinal cord transmits messages to and from the brain and also to the PNS.

  Peripheral Nervous System (PNS): Made up of the nerves outside the CNS, allowing sensory information to be received from the whole body, and motor control of the body.
• Peripheral Nervous System (PNS): Somatic nervous system.


  Somatic nervous system:

  -Made up of nerves emerging from the brain and the spine. Nerves contain both sensory neurons and motor neurons.

  -Sensory relay messages to the CNS and motor relay info from CNS to the body.

  -Somatic nervous system allows your CNS to receive sensory information from around the body and to make conscious muscle movements.

  -It is involved with reflex actions. It is the somatic nervous system nerves in the spinal cord which generates the command to pull away from a hot stove.
• Peripheral Nervous System (PNS): Autonomic nervous system.

  - Controls automatic processes.

  -Transmits information to and from internal organs to sustain essential processes required for life.

  -This include involuntary movements (startle response), heartbeat and breathing

  -Is made up entirely of motor pathways

  -Commands come from the brain stem (at the bottom of the brain where it joins the spine)

  -It has two parts - the sympathetic and the parasympathetic ANS. These work in opposition to each other, with the sympathetic ANS stimulating organs and tissues and the parasympathetic ANS inhibiting them.
• The structure and function of sensory, relay and motor neurons:

  Neurons.


  Neurons are cells that are specialised to carry neural information throughout the body. Neurons can be one of three types. They typically consist of:

  -A cell body (the control centre of the neuron)

  -Dendrites (at one end of the neuron, receiving signals from other neurons or from sensory receptors)

  -And an axon (carries the impulse to the axon terminal).
• The structure and function of sensory, relay and motor neurons:

  Sensory neurons:

  Sensory neurons:

  · Carry nerve impulses from sensory receptors found in the Peripheral Nervous System to the CNS. These receptors are e.g. in the eyes, ears, tongue and skin

  · Some neurons carry information from these receptors to the brain, which translates that information into sensations

  · Some neurons terminate in the spinal cord, which produces a reflex action more quickly as the information does not have to travel all the way to the brain
• The structure and function of sensory, relay and motor neurons:

  Relay neurons:


  Relay neurons:

  · These neurons go in between the sensory inputs (from the PNS to the CNS) and the motor output (from the CNS back to the PNS to control muscles and glands)

  · Relay neurons therefore allow sensory and motor neurons to communicate

  · These can be found only in the brain and spinal cord. Relay neurons in the brain also allow for cognitive processes and decision making
• The structure and function of sensory, relay and motor neurons:

  Motor neurons:

  Motor neurons:

  · Motor neurons start in the CNS, but send their axons outside the CNS to control muscles and glands.

  · Motor neurons form synapses with muscles and control their contractions. When stimulated the motor neuron releases neurotransmitters that binds to receptors on the muscle and trigger a response of muscle movement

  The strength of the muscle contraction depends on the rate of firing of the axons of motor neurons
• The structure and function of sensory, relay and motor neurons:

  
• The process of synaptic transmission:

  The process of synaptic transmission:

  1. An action potential travels down the axon of a neuron

  2. This action potential arrives at the end of the pre-synaptic terminal, but cannot cross the synaptic gap separating it from the dendrite of the next neuron

  3. The whole structure of the synapse involves the end of the presynaptic neuron, the membrane of the postsynaptic neuron, and the gap in between them.

  4. The presynaptic neuron releases vesicles into the synaptic gap. These vesicles contain chemical messengers known as neurotransmitters.

  5. These released neurotransmitters diffuse across the synaptic gap to the membrane of the postsynaptic neuron.

  They can either be excitatory (stimulate firing) or inhibitory (making firing less likely) - see the next box
• Neurotransmitters are either excitatory or inhibitory


  Neurotransmitters are either excitatory or inhibitory

  The neurotransmitters that are released into the synaptic gap can have one of two actions:

  1) Excitatory neurotransmitters include acetylcholine and noradrenaline. These make the postsynaptic neuron more likely to fire (because they excite the postsynaptic neuron).

  2) Inhibitory neurotransmitters include serotonin and GABA. These make the postsynaptic neuron less likely to fire (inhibit means to stop something).

  
  

  What follows is the process of summation.
• Summation


  The axons of multiple presynaptic neurons connect to the dendrites of a postsynaptic neuron. This means the postsynaptic neuron can receive information from multiple neurons in the form of different neurotransmitters.

  When this happens, the postsynaptic neuron has to calculate whether or not to fire. It does this through summation, which simply meaning summing up (adding up) the effects of the different neurotransmitters.

  
  

  If the neurotransmitters are overall excitatory the postsynaptic neuron fires (and at a higher rate). If they are overall inhibitory it fires less or not at all.
• The process of synaptic transmission

  
• Ending the fight or flight response (the parasympathetic nervous system)


  Ending the fight or flight response (the parasympathetic nervous system)

  When the threat has passed the fight or flight response does not need to continue. The parasympathetic branch of the autonomic nervous system reverses the changes made by the sympathetic nervous system to bring the whole body (including heartrate) back to its normal resting state. This is because the parasympathetic and the sympathetic branch work in opposition to each other.
• The sympathetic branch of the ANS causes adrenaline to be released.


  Change / Reason

  -Increased heart rate/ to increase blood flow to organs and increase the movement of adrenaline around the body

  -Increased breathing rate/ to increase oxygen intake

  -Pupil dilation/ To increase the light entry into the eye and enhance vision

  -Sweat production/ to regulate temperature.

  -Reduction of non essential functions/ to increase energy for other functions.
• The parasympathetic branch of the ANS reverse these changes, bringing the body back to its normal resting state.


  Sympathetic state/ parasympathetic state:

  -Increases heart rate/ decreases heart rate

  -Increases breathing rate/ decreases breathing rate

  -Dilates pupils/ constricts pupils

  -Inhibits digestion/ stimulates digestion

  -Inhibits saliva production/ stimulates saliva production

  -Contracts rectum/ relaxes rectum.
• Localisation of function in the brain:


  Localisation vs holistic theory: is the brain made up of connected areas that carry out specific functions (localised) or does the whole brain work together (holism)

  
  

  Broca and Wernicke discovered that particular areas of the brain were associated with particular functions (i.e. localisation). They disagreed with earlier scientists who believed that all parts of the brain were involved in the processing of information, thoughts and action (holism).

  If localisation is correct, damage to particular areas of the brain will always produce particular problems with function.
• Localisation and function: Motor and somatosensory centres


  -Motor cortex is responsible for generating voluntary motor movements. Both hemispheres have a motor cortex, with each being responsible for the opposite side of the body (left hemisphere controls right side of body). Therefore damage to your motor cortex on the left side of your brain will mean you have trouble moving the right side of your body.

  -Somatosensory cortex detects sensory information from touch, producing the sensation of touch, pressure, pain and temperature. Damage here means information from the senses is not being processed by the brain as it normally would.
• Localisation and function: Visual and auditory centres:

  -Visual cortex is located at the back of the brain, with the optic nerve travelling from the eyes (at the front) to the back. It spreads over both hemispheres, again with each responsible for the opposite side of the visual field (left hemisphere visual cortex processes images from the right side of the visual field). Damage here means difficulty processing visual information.

  -Auditory centres are in the temporal lobes of both hemispheres, not far from the ears themselves. They recognise sounds, and also analyse speech based information. Damage here means difficulty processing auditory information.
• Language production centre: Broca's area

  · This area was discovered by Paul Broca, who studied patients who could understand language but not produce language (they could not speak or write).

  · Through post-mortem examinations, he found lesions in the left frontal hemisphere of these patients.

  · Through this he discovered that this area of the brain is critical for speech production.

  
  

  Damage to this area causes Broca's aphasia. This is when their language production (spoken, written) is slow and takes a lot of effort. This is because their speech production is damaged.
• Language understanding centre: Wernicke's area


  · Wernicke had patients who could speak (so did not have damage to their Broca's area) but did not understand language.

  · Therefore they could talk (saying words) but these did not add up to sentences that made sense.

  · They had damage to the posterior portion of the left temporal lobe.

  · This area of the brain is therefore linked to recognising sounds as language and associating that language with meaning.

  
  

  Damage to this area causes Wernicke's aphasia. Patients with this condition produce language easily, but it is meaningless.
• Localisation Evaluation Strength


  Strength: research evidence to support that many neurological functions are localised.

  Petersen et al used brain scans to demonstrate how Wernicke's area was active during a listening task

  and Broca's area was active during a reading task.

  Shows that they have different functions, Wernicke's was needed to understand the language that was being listened to, whereas Broca's was needed in the

  production of language for the reading task.

  Supporting the theory of localisation as an explanation for behaviour.

  One strength of this research is that they used brain scans. Brain scans are an objective measure as the results cannot be changed by the researcher (researcher bias) or by the participant (demand characteristics like social desirability).

  Therefore that the results of this study are not affected by extraneous variables, and have high internal validity, meaning that the fact they show localisation of

  function can be trusted.
• Localisation evaluation Strength


  Strength: Research support for localisation from case studies where patients have suffered from neurological damage.

  Phineas Gage was injured when a pole went through his left cheek, passing it behind his left eye, and exiting

  his skull from the top of his head taking a portion of his brain with it- most of his left frontal lobe.

  The damage to his brain had caused a change in his personality. He went from being someone who was

  calm and reserved to someone who was quick tempered and rude.

  This show that damage to an area of the brain can lead to specific changes in our personality

  Therefore, this supports localisation of function as it suggests that aspects of our personality could

  be localised to our frontal lobe.

  However it uses a case study which could mean that these results may not be generalised. Just because Phineas Gage's personality was localised in this way, it

  does not necessarily mean that this localisation of function would be true for everybody.
• Localisation Evaluation Weakness


  Weakness: there is research evidence that refutes that higher cognitive functions are localised.

  Lashley removed areas of the cortex (between 10 and 50%) in rats that were learning a maze. No area was proven to be more important than any other in terms of the rat's ability to learn the maze.

  This suggests that their brains are not necessarily localised in terms of learning the maze. Therefore, this would support holistic theory rather than localisation

  However, this was conducted on rats which could be a problem because there is the issue of animal

  extrapolation, may not be able to generalise these results.

  Therefore, it could be that the rat's brains did not show localisation of function and showed

  holism, but human brains may not necessarily show holism in the same way.
• Hemispheric lateralisation:


  Hemispheric lateralisation:

  · Hemispheric lateralisation refers to the idea that 1 side of the brain controls the opposite side of the body and each hemisphere is responsible for different day to day functions

  · For example research has found that the left hemisphere is dominant for language and speech (Broca's and Wernicke's language centres are in the left hemisphere).

  The two hemispheres are connected by the corpus callosum, a bundle of nerve fibres.
• split brain patients


  Split-brain patients:

  · Starting in the 1940s, surgery was used to help patients with severe epilepsy.

  · This surgery involved cutting the corpus callosum either partly or entirely - commissurotomy.

  · The result of this was the patients had two separate brain hemispheres that could no longer communicate through the corpus callosum - they now had a 'split-brain'.

  Sperry studied the effects of this in order to investigate whether the two hemispheres were specialised to the point they operated independently of each other.
• Sperry's split-brain research - example procedure:


  · Split-brain patients would have an image projected to their right visual field (processed by the left hemisphere) or a different image projected to the left visual field (processed by the right hemisphere).

  Presenting the image to one hemisphere of a split-brain patient meant the information would only be perceived by one hemisphere (due to the corpus callosum surgery). Patients were asked to focus on the fixation point whilst one eye was covered.

  A word is flashed to their right field view and they are asked to say what he saw. (Left hemisphere is dominant for verbal processing). A word is flashed to his left field view and he is unable to say it but can draw it. (Right hemisphere cannot share information).
• Sperry's split-brain research - findings:

  · Ppts could only describe what they saw when it was shown to their left hemisphere (which contains both language centres), not to their right hemisphere. As you can see from the diagrams below, you show items to the left hemisphere through the right visual field.

  · This was true for held items also - a patient touching an item with their left hand could not describe it (as this information goes to the somatosensory cortex in the right hemisphere - which does not have the language centres). Whilst they couldn't describe what word was seen by the left visual field, they could use their left hand to select an object most closely related to that word.

  · When doing a task involving matching faces to pictures, the right hemisphere was dominant for this (higher accuracy when faces shown on left visual field to right hemisphere). This shows that facial recognition is lateralised to the right hemisphere.
• Hemispheric lateralization (split-brain theory) evaluation strength

  Sperry's research shows that the brain is lateralised as it would seem that certain halves of the brain are specialised for different tasks. EG. the left half is for language and the right is for faces. This supports hemispheric lateralisation.
• Hemispheric lateralization (split-brain theory) evaluation weakness

  Weakness: Very hard to find participants in the modern day, with many studies only using one participnats, reducing the ability to generalise the findings to society. An example of this is Sperry's study. Sperry's study consisted of a small and unusual sample of 11 people with a history of epileptic seizures, and so is in no way representative of the general population reducing its generalisability .

  • This is because all participants had a history of epileptic seizures, and so it could be argued that this medical background could have caused changes to the brain. Therefore, the 'normal' brain may act different if it undergoes a commissurotomy.

  • And so this idiographic approach to studying the split brain cannot be generalized to the wider population due to reduced population validity, as we cannot say that a normal individuals brain works to the same degree as those with prior medical conditions.

  
  

  -Lacks internal validity as there could be many confounding variables.

  - This is because Sperry's control group consisted of 11 people with no cut brain and no history of epilepsy. By changing two variables at one time, we cannot be sure whether the difference between the groups is due to the presence of epilepsy or the split brain. Thus, we cannot generalise his results to the wider population
• Hemispheric lateralization (split-brain theory) evaluation weakness

  Weakness: Split brain research showed that the right

  hemisphere could not handle any language.

  However a recent case study found that Kim

  Peek who was born without a Corpus Callosum,

  had developed language areas in both

  hemispheres.

  Suggests that the brain may not be lateralised in all people in the same way. We would expect a brain that supports hemispheric lateralisation to have language specialised to the left side but Peek's does not. This questions hemispheric lateralisation.

  However, since case studies are idiographic it means Peek's data could be unique and may not be applied to others the same way. Should not be generalised.
• Hemispheric lateralization (split-brain theory) evaluation strength

  • One strength of the lateralisation theory is that it makes use of highly specialised and standardised procedures.

  • For instance, they standardized the stimuli that each participants processed, and for how long it was flashed onto the screen, as well as standardised things like the fixation point. This allowed them to change certain variables, such as what image or word was flashed, and to which visual field it was shown to, to study each hemisphere individually.

  • Due to its highly controlled procedure, its highly replicable and has good internal validity
• Plasticity and functional recovery of the brain after trauma.

  Plasticity:

  · This is also known as neuroplasticity and cortical remapping. It is the brain's ability to change and adapt (in both function and in physical structure) as a result of experience and learning.

  An infant's brain experiences a rapid growth in the number of synaptic connections it has, peaking at 15,000 by the age of 3 years old. This is twice as many as there are in the adult brain: connections that are rarely used are deleted through 'synaptic pruning'. This is just one example of plasticity.
• Research into plasticity:


  · Maguire et al (2000) studied the brains of London taxi drivers and compared them against a control group. This is because taxi drivers have to remember the map of London's streets.

  · They found significantly more volume of grey matter in the posterior hippocampus in the taxi drivers than in a matched control group. This part of the brain is associated with the development of spatial and navigational skills in humans and other animals.

  This difference shows plasticity.

  · However, we cannot be sure whether the taxi drivers have a naturally denser hippocampus, or whether it was their undertaking of the knowledge that led to this.

  · Although, they found that the longer the drivers had been in the job, the more pronounced the structural difference (stronger positive correlation).
• Functional recovery of the brain after trauma:

  · Following injury, unaffected areas of the brain are able to adapt and compensate for those areas that are damaged. This is an example of neural plasticity.

  · Healthy brain areas may take over the functions of those areas that are damaged.

  · This can involve axonal sprouting: new nerve endings grows and connect with undamaged nerve cells to form new neural pathways

  · The brain is also able to form new synaptic connections close to the area of damage. Secondary neural pathways that would not typically be used to carry out certain functions are unmasked to enable functioning to continue.

  Another form of functional recovery is recruitment of homologous areas on the opposite hemisphere to do those tasks. This is called neural reorganisation. If Broca's area was damaged then the equivalent area in the right hemisphere could take on those functions instead.
• Research into functional recovery:

  · Tajiri et al provided evidence for the role of stem cells in producing functional recovery. They randomly assigned rats with traumatic brain injury to one of 2 groups. One group received transplants of stem cells into the region of the brain affected by traumatic injury. The control group received a solution containing no stem cells.

  · Three months after the brain injury the brains of stem cell rats showed clear development of neuron-like cells in the area of injury. The control group did not.

  This is strong evidence of functional recovery, as the stem cells produced new cells in the damaged area of the brain.
• Plasticity and functional recovery evaluation strength

  Maguire found that there was more grey matter in the posterior hippocampus , an area associated navigational skills, than a matched control group in the brains of taxi drivers, after learning "the knowledge" i.e. the map of London's streets for their job.

  This shows that there is support for plasticity in the brain as the brains of the taxi drivers have changed through the experience of learning.

  However, the study only uses taxi drivers. This is a limited sample and only tests one type of person. Lack population validity as it is not generalisable. Therefore, there is support for plasticity in the brain for taxi drivers but cannot be sure if it's the same for others. There is an issue with cause and effect.

  
  

  Bezzola observed reduced motor cortex activity in novice golfers aged 40 - 60 compared to a control

  group.

  Therefore, they were more efficient neurally after training, i.e. training had made their "golf brains"

  better.

  This therefore shows support for plasticity in the brain as the golfer's brain had developed through the practice of golf. Also suggests plasticity continues through our lives regardless of age.

  However, this was only tested with golf so it cannot be generalised to the population. Lacks external validity.
• Plasticity and functional recovery evaluation strength

  One strength of understanding plasticity is that it has contributed to the field of neurorehabilitation. By recognising the process of spontaneous recovery, such as how the recovery slows after a few weeks and that the brain can only fix itself to a certain degree, means that we can now roll out additional therapies and treatments to gain the best possible recovery for the patient. Thus, our understanding has furthered medical treatments, and has beneficial real world application.
• Plasticity and functional recovery evaluation strength


  Hubel and Wiesel found that when they sewed one eye of a kitten shut, and analysed the brain's

  response, the area of the visual cortex to do with the shut eye was not idle (which is what they thought

  would happen)

  Instead, it continued to process information from the open eye.

  This shows that there is support for plasticity and functional recovery in the brain. brain had adapted to the damage, shows support for functional recovery.

  However, there is an issue with animal extrapolation as the study was only conducted on kittens. Cannot be generalised or applied to humans.
• Ways of studying the brain: scanning techniques

  Functional magnetic resonance imaging (fMRI):

  · fMRI works by detecting the changes in oxygenated blood flow that occurs as a result of neural (brain) activity (haemodynamic response) in specific parts of the brain.

  · An active brain area consumes more oxygen., meaning blood flow is directed to that area.

  fMRI produces 3D images that are activation maps, showing which parts of the brain are using larger amounts of oxygen and are therefore more active.
• Electroencephalogram (EEGs):


  Electroencephalogram (EEGs):

  · EEGs measure electrical activity within the brain via electrodes that are fixed on the scalp, usually using a skull cap.