Explain, using one or more examples, the effects o
When a nerve impulse reaches the end of the neuron, the neuron fires and neurotransmitters are released into the synaptic gap where they travel to the neuron at the other side of the synaptic gap.
If the neurotransmitter is not absorbed it can be re-uptaken, disffused out or destroyed. The neurotransmitter then binds to specific receptors at the other side. If a neurotransmitter is blocked or replaced then the messages chance. This affects the phsiological system, cognition, mood, or behaviour.
Dopamine is a neurotransmitter involved in goal-directed behaviour such as pleasure seeking, control of movement, emotional response, and addictive behaviour. Dopamine is released in the brain's reward system.
Dopamine and addictive behaviour
- Dopamine is released in the brain's reward system and has been associated with pleasure seeking and addictive behaviour. Addictive drugs or substances increase the amount of dopamine in the reward system.
- Dopamine can be relased by environmental triggers (e.g. the sight of a cigarette package, food, or a gambling machine) becaise this is associated with pleasure (reward).
- Nicotine is the psychoactive ingredient in tobacco, which increases the level of dopamine in the brain's reward circuit causing feelings of pleasure and relaxation.
Berridge and Kringelbach (2009) on dopamine in pleasure seeking
fMRI scans were used to study brain areas involved in the subjective experience of pleasure. They found that the orbitofrontal cortex was active when people reported feeling pleasure.
The researchers concluded that: dopamine and the nucleus accumbens is perhaps rather involved in pleasure seeking. This could explain addictive behaviour.
The orbitofrontal cortex and natural opiods (endorphins) are perhaps linked to the subjective experience of pleasure.
Fisher (2004) on dopamine in ''addiction to love''
This is an evolutionary explanation of behaviour. "Being in love" has similarities with "being addicted" according to Fisher.
- Dopamine increases desire and reward by triggering the same emotional rush of pleasure when you see or think of the loved one as if you were taking a drug like cocaine.
- Dopamine can explain the highs of romantic passion (High levels of dopamine) and the lows of rejection (Low levels of dopamine).
Acetylcholine (ACh) on memory
- ACh is a neurotransmitter which has been linked to synaptic plasticity in the hippocampus and it seems to play an important role in learning and short-term memory via the cholinergic system (Shinoe et al. 2005).
- The cholingergic system is a system of nerve cells that uses acetylcholine in transmitting nerve signals. Memory processing and higher cognitive functioning are dependent on the cholinergic system.
Martinez and Kesner (1991) ACh in memory formation
Aim is to investigate the role of ACh in memory formation. The procedure is that it is an experimental study which uses rats. They were trained to run a maze. The were divided into three groups.
- Group 1: received injection with scopolamine (blocks ACh receptor sites reducing available ACh)
- Group 2: received injection with phsotigmine (blocks production of cholinesterase (enzyme) which cleans up ACh from the synapses) leading to more available ACh.
- Group 3: The control group.
- Group 1 had problems finding their way through the maze and made more mistakes.
- Group 2 ran quickly through the maze and made few mistakes. The group was quicker than the control group.
The study shows that ACh is important in memory since the rats showed different memory capacity depending on ACh level. Since this was a controlled laboratory experiment, it can be concluded that the level of ACh is one factor that affects memory but the neurobiology of memory is very complex.
Explain, using examples, the function of two hormo
Cortisol and memory
Cortisol is a hormone produced by the adrenal cortex in response to stress and to restore homeostasis. Chronic stress may result in prolonged cortisol secretion and this can lead to physiolgogical changes such as damaged immune system and impairment of learning and memory. This is because high amounts of cortisol results in atrophy in the hippocampus (Sapolsky, 1996).
Newcomer et al (1999) Experiment on cortisol and memory
Aim: To investigate how levels of cortisol interfere with verbal declarative memory.
Procedure: A self selected sample (recruited through adcertisement) of 51 normal and healthy people aged 18-30 was used, It was a rabdinuzed, controlled, double-blind experiment running for four days, All participants gave informed consent. There were three experimental conditions:
1. A high level of cortisol (Tablet of 160 mg per day), equivalent to cortisol levels in the blood as a consequence of a major stressful event.
2. A low level of cortisol (tablet of 40 mg per day), equivalent to cortisol levels in the blood as a consequence of a minor stressful event.
3. A placebo (tablet of no active ingredient).
Results: The high-level group performed worse on the verbal declarative memory test than the low-level group. They performed below placebo levels after day 1. The low-level group (mild stress) showed no memory decrease.
Evaluation: This was a controlled randomized experiment so it was possible to establish a cause-effect relationship between levels of cortisol and scores on a verbal declarative memory test. Ethical issues were observed with informed consent. The negative effect of taking high dosages of cortisol was reversible so no harm was done.
Oxytocin and trust
- The hormone oxytocin is secreted by the hypothalamus and released (1) into the blood stream via the pituitary gland or (2) into the brain and spinal cord where it binds to oxytocin receptors. Oxytocin acts primarilt as a neurotransmitter in the brain.
- Oxytocin has been linked to trusting other people. Experimental manipulation of oxytocin levels has shown increase in trust.
- According to ecolutionary psychologists, trust is an important social tool in the relationship between humans. Trust is an adaptive mechanism as it helps humans to form meaningful relationships at a personal and professional level. Betrayl disrupts bonds of trust.
- Learning who to trust and who to avoid is important for survival and the well-being of an individual. Humans should also be able to move on after experiences of breaching trust if long-term relationships and mental well-being are to be preserved.
- Oxytocin could play a role in reducing fear reactions via the amygdala that may arise as a consequence of betrayal.
Baumgartner et al (2008) The role of oxytovin in trust in economic behaviour
Aim: To investigate the role of oxytocin after breaches of trust in a trust game.
- The participants played a trust game used by economists and neuroscientists to study social interaction. The "investor" (player 1) recieves a sum of money and must decide whether to keep it or share it with a "trustee" (player 2). If the sum is shared the sum is tripled. Then player 2 must decide if this sum should be shared (trust) or kept (violation of trust).
- fMRI scans were carried out on 49 participants. They received either oxytocin or placebo via a nasal spray.
- Participants played against different trustees in the trust game and against a computer in a risk game. In 50% of the games their trust was broken. They received feedback on this form the experimenters during the games.
- Participants in the placebo group were likely to show less trust after feedback on betrayal. They invested less participants in the oxytocin group continued to invest at similar rates after receiving feedback on a breach of trust.
- The fMRI scans showed decreases in responses in the amygdala and the caudate nucleus. The amygdala is involved in emtoional processing and has many oxytocin receptors. The caudate nucleus is associated with learning and memory and plays a role in reward-related responses and learning to trust.
- Oxytocin could explain why people are able to restore trust and forgive in long-term relationships.
- Scanner research is merely mapping brain activity but nothing definite can be said about what it really means at this point in science.
- Giving oxytocin like this in an experiment may not reflect natural physiological processes. The function of oxytocin is very complex and it is too simplistic to say that it is "the trust hormone".
Discuss two effects of the environment on physiolo
Effect 1: Environmental effects on dendritic branching (brain plasticity)
- Environmental stimulation refers to the way the environment provides stimulation in the form of social interaction and learning opportunities for animals and humans. Experiences are processed in the brain's nervous system, and stimulating environments will result in increased numbers of synapses.
- An enriched environment is characterized by multiple opportunities to learn new things. Researchers have used animal models to study synaptic changes in the brain because it is not possible to use humans in deprivation experiments.
- Instead researchers use case studies of children who have grown up in total neglect, i.e. with little or no experience of language, touch and interaction with other humans. The brains of neglected children are often smaller and there is scientific evidence of altered brain function.
Rosenweig, Bennet and Diamond (1972) The role of environmental stimulation on brain plasticity
Aim: To investigate whether environmental factors such as a rich or an impoverished environment affect development of neurons in the cerebral cortex.
- Rats were okaced ub eutger ab ebrucged ebcuribnebt (EC) or an impoverished condition (IC).
- EC: 10-12 rats in a cage provided with different stimulus objects to explore and play with. This group also received maze training.
- IC: each rat in an individual cage (isolation and no stimulation).
- The rats typically spent 30 to 60 days in their respective environments before they were killed so the researchers could study changes in brain anatomy.
- The anatomy of the brain was different for rats in the EC and the IC.
- The brains of EC rats had increased thickness and higher weight of the cortex. EC rats had developed more acetylcholine receptors in the cerebral cortex.
- The experiment was a rigorously controlled laboratory experiment so it was possible to establish a cause-effect relationship.
- The experiment used animal models and therefore it may be difficult to generalize to humans unless research with human provides the same results.
- Follow-up of this research indicated that just 2 hours a day in an enriched environment produced the same plastic changes in the brain as in rats that had been constantly in the EC condition. This shows that the brain can change and adapt to new situations.
Effect 2: Environmental stressors and hippocampal damage in PTSD patients
- A stressor is any event that threatens to disrupt the body's normal balance and starts a stress response such as secretion of stess hormones and acrivation of the 'fear sensor' in the brain, the amygdala.
- A stressor may be an acute stressor (e.g. being assaulted, having an accident) or it could be a chronic stressor (e.g. anticipation of violence or worrying).
- The fight or flight response (coping mechanism) is a pattern of physiological responses that prepares the body to deal with emergency. Sapolsky (1996) has shown in animal studies that long-term stress and a prolonged flow of cortisol can influence the size of the hippocampus, which plays a major role in memory.
Trauma and PTSD
- Traumatic episodes (i.e. frightening situations from which a person cannot escape) produce intense fear. In about 5% of the population this may lead to PTSD (post-traumatic stress disorder) with effects that can last for a brief period or a lifetime.
- Combat veterans and survivors of childhood sexual abuse who suffer from PTSD tend to have a number of stress related problems such as forgetfulness and difficultly learning. In such patients stress-related physiological changes have been observed in the brain, especially in the hippocampus, which play an important role in inegrating different aspects of a memory at the time of recollection.
Bremmer et al (2003) Stress, PTSD and memory problems related to reduction of hippocampal volume.
Aim: To measure the volume of the hippocampus based on the theory that proplonged stress may reduce the volume of the hippocampus due to increased cortisol levels.
- MRI scans were made of the brains of the participants and participants completed memoery tests (e.g. remembering a story or a list of words).
- The participants were veterans and female adults who had experienced early childhood sexual abuse. Some had developed PTSD, but not all.
- The researchers found that there were deficits in short-term memory and then performed MRI scans of the participants' brains.
- They found that the hippocampus was smaller in PTSD patients than in a control group. The veterans with most memory problems also had the smallest hippocampus.
- The findings showed a clear correlation between number of years of abuse as measured by a trauma test, memory problems and hippocampal volume.
- People suffering from PTSD often suffer from other psychological disorders (e.g. depression) which could perhaps also play a role in the observed changes in the brain.
- The sample was very small so it is difficult to say anything definite about the relationship between trauma and hippocampal volume.
- There could be alternative explanations to differences in hippocampal volume (e.g. that people who suffer from PTSD often suffer from depression as well). Depression is also associated with reduction of the hippocampus. However, the findings of a large reduction of hippocampal volume in combat-related PTSD has been replicated many times.