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Biological Level of Analysis
Terms in this set (54)
Reducing complex systems to simpler components that are more manageable to study
A concept that considers the whole person
Localization of Function
-The theory that different parts of the brain do different things.
-Although we know that some parts of the brain do play specific roles in behavior, rarely does a part of the brain work in complete isolation.
Central Nervous System
Consists of the spinal cord and the brain
Major Parts of the Brain
-The layer of neurons with a folded surface covering the brain on the outside
-It is the largest part of the human brain associated with higher-order functions such as abstract thought ot voluntary action.
-Evolutionarily, this part of the brain developed the latest.
-The cortex is divided into four sections called "lobes"
Associated with reasoning, planning, thinking, and decision-making, voluntary action, complex emotions, and so on.
Associated with movement, orientation, perception, and recognition.
Associated with visual processing
Associated with processing auditory information, memory, and speech.
-Area at the rear of the frontal lobes that controls voluntary movement.
-Different parts of the cortex controls different parts of the body - the left hemisphere controls the right side of the body and visa versa.
-Located in the front of the parietal lobes
-Registers and processes body senses
A structure of neurons that connects the left and right hemispheres of the brain
-Associated with coordination, movement, and balance.
-An evolutionarily older subcortical structure. It is sometimes referred to as the "emotional brain"
-Has mostly sensory functions
-Nerves from almost all sensory organs reach the thalamus as a final "hub" before they are connected to the cortex
-Located below the thalamus
-It is involved in functions such as emotion, thirst, and hunger
Involved in memory, emotion, and fear
Important for such functions as learning,
memory, and transferring short-term memory to a more permanent store, spatial orientation
Plays a role in habit-forming and procedural
Plays a role in addiction and motivation
-Underneath the limbic system
-Its main function is to regulate the basic vital processes such as breathing or heartbeat
-It connects the brain to the spinal cord
-This part of the brain is very much like the entire brain found in lower animals such as reptiles
Today's researchers are continuing to try and map the brain. They are doing this my looking at neural connection in the brain and creating a map called connectome.
-Aim: To better understand the effects that the surgery had on patient HM
-Method: A longitudinal case study was performed on HM. He was hit by a cyclist while crossing the road when he was 7 and sustained a serious head injury. When he was 10, he began receiving epileptic attacks. At 27 he became so incapacitated due to the seizures that he could not lead a normal life and medication did not help him. With approval from HM and his family, William Scoville performed an experimental surgery where he removed tissue from the medial temporal lobe (including the hippocampus) on both side of HM's brain. Brenda Miler studies HM until he died in 2008. The first time Milner visited HM after the operation she observed that he forgot daily events nearly as fast as they occurred. After the operation HM remembered his childhood well. He later experienced retrograde amnesia and had a difficult time remembering the period about a year prior to the operation. He primarily suffered from anterograde amnesia (can not create new memories). Milner used method triangulation to carry out her studies. She used: psychometric testing(IQ testing), direct observation, interviews, cognitive testing (memory recall tests, like reverse mirror testing), and later an MRI.
-HM could not acquire new episodic (memory for events) or semantic (general knowledge about the world) knowledge. This suggests that the brain structures that were removed from his brain are important for the transfer of information from short term to long term memory.
-HM was able to remember his house and could draw a picture of the floor plan of his new home. This indicates that he was able to form a cognitive map of the spatial layout of his house. This may mean that this type of memory is not encoded in the same way as semantic or episodic memories.
-HM had a capacity for working memory, since he was able to carry on a normal conversation. This requires a minimal level of retention of what has just been heard and said. On being asked to recall the number 584, HM was able to do so even 15 minutes later, apparently by means of constant rehearsal. However, after the task was over, HM would not be able to recall the number
-Memories in the form of motor skills, i.e. procedural memories, were well maintained; for example, he knew how to mow a lawn. He also showed improvements on the performance of new skills such as reverse mirror-drawing in which he had to acquire new eye-hand coordination (Milner, 1966). Although he showed improvement on the skill over time, he never remembered learning the skill. Every time Milner asked him to do it, he would say that he had never tried it before
-In 1992 and then 2003, Corkin carried out an MRI scan of HM's brain to see the extent of the damage. It was possible to see that parts of HM's temporal lobe including the hippocampus had the most damage. However, the damage was less extensive than originally estimated by Scoville. Damage to the hippocampus explains the problem of transferring short-term memory to long term memory as this is the area where the neurotransmitter acetylcholine is believed to play an important role in learning and formation of memories.
-The memory systems in the brain constitute a highly specialized and complex system.
-The hippocampus plays a critical role in converting memories of experiences from short-term memory to long-term memory.
-However, researchers found that short-term memory is not stored in the hippocampus as HM was able to retain information for a while if he rehearsed it.
-Since HM was able to retain some memories for events that happened long before his surgery it indicates that the medial temporal region is not the site of permanent storage but rather plays a role in the organization and permanent storage of memories elsewhere in the brain.
-Implicit memory contains several stores - for example, procedural memory, emotional memory and skills and habits. Each of these areas is related to different brain areas.
-Longitudinal case study
-High ecological validity
-Cannot easily be replicated
-Retrospective in nature
-Ethics - confidentiality (name was found out after his death), consent (HM was incapacitated and could not remember things
Corkin (1997, 2002)
-Aim: To investigate the extent of the hippocampal and medial temporal lobe damage to HM's brain and to determine whether this could be sufficient to have resulted in the drastic memory loss suffered by HM.
-Method: HM was hit by a cyclist while crossing the road when he was 7 and sustained a serious head injury. When he was 10, he began receiving epileptic attacks. At 27 he became so incapacitated due to the seizures that he could not lead a normal life and medication did not help him. With approval from HM and his family, William Scoville performed an experimental surgery where he removed tissue from the medial temporal lobe (including the hippocampus) on both side of HM's brain. Corkin had known HM since 1962, during with time he had never recognized her from one visit to another. Corkin and her colleagues used MRI scanning in 1992 and 1993 to determine if Scoville's estimated lesioning of HM's temporal medial lobe atea had been as he stated, and whether this could be sufficient to have resulted in the drastic memory loss suffered by HM. Before the 1992 MRI scan, HM completed an IQ test and a memory test. The IQ test showed that he had normal intelligence, but the memory test showed that he had a memory quotient that was 37 points lower than his IQ and showed that he had severe amnesia.
-Both scans showed that the lesioning (also called ablation or cutting) of HM's brain was 3 cm less than Scoville had estimated. It therefore did not extend as far into the posterior hippocampal region as he thought, although there was surrounding damage, as stated, to the uncus and the amygdala. Approximately 50% of the posterior hippocampus on each side remained, but this had shrunk considerably on the right side. Corkin believed that this could be due to both the removal of the rest of the hippocampus, and also to the druge and continuing (much reduced) epileptic seizures.
-The small amount of normal hippocampus remaining in the left temporal lobe was not sufficient to support normal memory. Therefore, this study demonstrates the importance of the hippocampus and the temporal medial lobe area for memory.
-Ethics: Milner gave permission for Corkin to scan HM's brain. It is not clear if she was the appointed responsible adult legally able to do this. HM, even if he gave permission himself, would not have remembered it, so there are issues with informed consent and right to withdraw.
-Ethics: Anonymity was maintained until his death.
An inability to form new memories
Knowledge for events
General Knowledge about the world
Memories for the performance of actions or skills ("knowing how")
-Aim: To investigate whether large lesions on the medial temporal lobe is responsible for the formation of long term memory
-Method: In 1992, Larry Squire and his team were introduced to one of the most interesting cases of amnesia since the famous HM study. At the age of 70, Eugene Pauly was diagnosed with viral encephalitis. His physical recovery was amazing, but his cognitive impairment was very significant. He had large lesions on his medial temporal lobe, the part of the brain responsible for the formation of long-term memory. Both the amygdala and the hippocampus were completely destroyed. When he returned home with his wife, the results of this cognitive impairment began to show. He couldn't remember the day of the week, the names of nurses or doctors or friends. He had trouble following a conversation but could talk about topics that interested him. Often he would repeat the same story or comment several times in a single afternoon. He would often forget what he had already done and as a result he would eat breakfast several times in a single day. Although he could not form new declarative memories, he could recall and discuss most of the events of his life that happened prior to 1960. - three decades earlier. Unlike HM, he was still socially functional. Whenever someone walked in the room, he would introduce himself and ask them about their day. Squire carried out a series of interviews with EP at his home. During one interview he asked EP to draw a map of his home. He was not able to do it. However, EP excused himself and got up to go to the toilet. How could a man that could not draw a map of his home find the bathroom on his own? When sitting in the living room, he could not identify which door led to the kitchen. But if Squire asked him to get him something to eat, he immediately got up and headed for the kitchen. This was a behavior not seen in HM. It led Squire and his team to carry out a case study that would deepen our understanding of how memory works. In this case study, Squire and his team used several different methods: interviews, psychometric testing, observations, and MRI's. One of the important tests done was the Autobiographical Memory Interview. The AMI is a structured interview that asks for detailed information about three periods of life: childhood, early adult life, and recent life. Within each of these periods EP's memory was tested for both personal semantic knowledge and autobiographical memory. The accuracy of all his responses was verified by at least two family members. For the recent time period, EP performed extremely poorly. He did better at answering questions about his early adult life, but his scores were still below the control scores. In contrast, EP performed normally when answering questions about his childhood, scoring nearly as high as the highest-scoring control subjects. Another important finding was an experiment in which Squire took 16 different objects and glued them on cardboard rectangles. He then organized the objects in 8 pairs. On the bottom of one of the objects in each pair was written the word "correct." EP had to choose between the two with the goal that with rehearsal, he would be able to consistently choose the "correct" object. However, he couldn't remember which objects were correct. The experiment was repeated twice a week for months. On each day that the experiment was repeated, there were 40 pairings. The findings were surprising. After 28 days he was choosing the correct object 85% of the time; after 36 days he was right 95% of the time. He would even turn the objects over on his own, even though he didn't remember that there would be a sticker there, as he could not recall ever doing the task. Squire wanted to see if this was true learning - that is, that Pauly actually remembered the objects, or whether there was something else happening. He then asked EP to put all the "correct" objects in a pile. He was unable to do so. He could only select the correct object from the consistent pairings.
-MRI indicated that EP's basal ganglia were undamaged. This explains why EP could find the kitchen and the bathroom. It also explained why he was able to make breakfast and other tasks that were "routine." Of course, this also explains Squires experiment with the pairing of objects.It also explains another phenomenon which EP's wife reported. EP was able to take a walk around the block by himself, since his wife had taken him on a daily walk around the block after his surgery. She would even follow him around the block to make sure that he was ok, but he was able to find his way home without any problems. When he was asked from any point on his walk where he lived, he would say he didn't know, but since the task was associative - or a habit - he was able to simply walk home. However, occasionally there was a problem. If the sidewalk was being repaired and he had to leave his familiar path, EP would get lost. Returning to our example of driving a car - even when we drive a long time, bad weather or heavy traffic forces us to concentrate more. The task reverts from associative to cognitive. When this happened to EP, he did not have the capacity to solve the problem as his memory was only procedural. Once the familiar pattern was changed - as when Squire asked him to put the objects in piles - he was unable to complete the task.
-The conclusions of this case study show us that memory is more complex than initially believed and that the creation of memories is not solely dependent on the hippocampus. Even with hippocampal damage, tasks may be learned - even though the individual may not remember learning the task. In the case of HM, he was taught to draw using a mirror, but he never remembered learning this. This was the result of the role of the basal ganglia.
-The research also showed that habits need to be triggered. A cue leads to a routine. When EP was cued to play the object identification game, the routine was triggered, telling the brain to go into automatic mode.
-Method triangulation was used
-In depth study
-Case study - unable to be replicated
-Ethics - anonymity (EP, aka Eugene Pauly's, name was found out), perhaps consent because EP had a bad memory
The loss of articulated speech
Case Study of "Tan"
-Real name: Louis Leborgne
-"Tan" lost the ability to speak at the age of 30
-He was admitted for surgery some time later for gangrene - Paul Broca was the surgeon
-Broca also happened to be a specialist in language
-By the time Broca was to perform the surgery, the only syllable Louis Leborgne could say was "tan". He often repeated it twice (tan-tan)
-There were no other malfunctions with Tan. His intelligence was intact, he understood everything he was asked and tried to communicate back
-Tan's condition became known as Broca's aphasia
-Tan's died at the age of 51, and an autopsy was performed. His brain showed a lesion in the frontal area of the left hemisphere, in particular region a in the posterior inferior frontal gyrus - now known as Broca's area.
-Broca did not rush to publish his findings with Tan. He studied 25 other patients with the same problem before finally asserting that speech articulation is controlled by the left frontal lobe.
-However, the area responsible to articulate speech may be more complex than originally thought. Tan's brain was re- examined 100 years later, and it turned out that the lesion had actually been broader than documented by Broca.
-Broca did not notice this detail because he decided to preserve Tan's brain intact rather than dissecting it.
-Discovered by Karl Wernicke
-It is located in the temporal lobe of the dominant
hemisphere (which is the left hemisphere for most
-Responsible for the comprehension of written and spoken language
-People with Wernicke's aphasia have a general impairment of language comprehension, while at the same time speech production is intact.
-When they speak they sound really fluent and natural, but what they say is in fact largely meaningless.
-Aim: To search for localization memory trace or engram
-Method: In a typical study he would train a rat to run through a maze without errors in search of food. After learning occurred, he would remove an area of the cortex, then place the rat back at the start of the maze and register the change in behavior. He removed varying portions of the cortex in different rats ranging from 10% to 50%. The idea was that if memory of the maze is localized somewhere, you will finally be able to pinpoint the specific region in the cortex responsible for it.
-Although it took the rats longer, they were still able to get through the maze.
-The search turned out to be a failure and Lashley abandoned his initial hypothesis, concluding that memory was distributed rather than localized.
-His conclusion is supported by two observations: The principle of mass action (based upon a correlation observed between the percentage of cortex removed and learning abilities. The less cortex, the slower and more inefficient the learning. The key idea here is that the performance deterioration depends on the percentage of cortex destroyed but not on the location of the destroyed cells) and equipotentiality (this refers to the ability of one part of the cortex to take over the functions of another part of the cortex)
-These observations led Lashley to believe that memory is widely distributed across the cortex
-Procedure is replicable
-Showed evidence to oppose localization of function
-Relative localization is still supported today
-Ethics - rats were harmed
Currently, neuroscience supports relative localization: it admits localization for some functions under some conditions, but it also clearly outlines limits of localization.
-Describes the changes in neural pathways and synapses due to changes in behavior,
environment, thinking, emotions, as well as changes resulting from bodily injury
-The change occurs through the making and breaking of synaptic connections between neurons
-In this process neural networks in the brain literally change their shape
-The reasons for such changes are both genetic (normal pre- programmed development of the brain) and environmental (ex - injury, brain damage, or simply learning new skills)
-Can be observed on different scales
-At the level of a single neuron, it take the form of synaptic plasticity
-On the largest scale, neuroplasticity takes the form of cortical remapping
-Is not confined to making up for damage. It occurs on a regular basis in our daily lives.
-When you learn, your brain gradually reshapes itself.
-The ability of the neuron to form new synaptic
connections and break up the old ones
-Depends on the activity of the neurons.
-If the nearby neurons are frequently activated at the same time, as synaptic connection between them may gradually form.
-Similarly, if two neurons are rarely activated together, the existing connection may gradually fall apart.
-"Neurons that fire together, wire together" and "neurons that fire out of sync, fail to link"
The phenomenon when brain area X assumes the function of brain area Y, for example due to injury
Merzenich et al (1984)
-Aim: To study the effect of neuroplasticity on the level of cortical remapping
-Method: Researchers studied the cortical representations of the hand in eight adult owl monkeys. There was a 3 step procedure. Step 1: Sensory inputs from all of the hand digits were mapped in the cortex. To do this, electrodes were inserted in the cortical area known to be responsible for sensation from the hand, then researchers stimulated various areas on the fingers one by one and noted which electrode was responding to the stimulation. The monkeys were anesthetized for this procedure. Step 2: the third digit (middle finger) on the monkey's hand was amputated. Step 3: 62 days later a mapping was done to see how the cortical area responsible for sensitivity from the hand changed after amputation.
-The first mapping showed that there were 5 distinct areas in the brain, each responsible for one finger, and adjacent fingers were represented in adjacent areas in the cortex.
-Post amputation found that the adjacent areas spread and occupied parts of the now unused area. The areas responsible for digits 2 and 4 became larger while the areas responsible for digits 1 and 5 stayed the same.
-Procedure is replicable
-Ethics - monkeys were harmed (finger was cut off)
Rosenzweig et al (1972)
-Aim: To investigate whether environmental factors such as a rich or an impoverished environment would affect the development of neurons in the cerebral cortex
-Method: Three male rats from a common litter were randomly allocated to one of three environments. In the control condition [CC] there were three rats in the cage. In the impoverished condition [IC], the researchers placed each rat in individual cages. The individual cages lacked the toys and the maze which were in the enriched environment. For the enriched condition [EC], the researchers placed 10 - 12 rats in a cage containing different stimulus objects to explore and play with. All groups had free and adequate access to food and water. The rats typically spent 30 to 60 days in their respective environments before they were killed in order for the researchers to study changes in the brain's anatomy.
-The anatomy of the brain was different in the EC and the IC. There was an increased thickness and higher weight of the cortex in EC rats compared to that of IC rats. The researchers also noted that rats in the EC condition had developed significantly greater activity in the neurons in the cerebral cortex associated with transmission of acetylcholine, which is an important neurotransmitter for learning and memory
-It appears that the thickness of the cortex and the overall weight of the brain increased as a result of the enriched environment. A follow-up to this research indicated that just 30 minutes a day in an enriched environment produced the same changes in the brain in rats as had been observed in the original experiment where rats were exposed to the EC condition for a much longer period of time.
-One variable that was not clear in the enriched environment is whether it was the environment (the toys) or the social activity. Putting rats alone in large cages with toys for two hours a day showed no effect. The single rat tended not to play with the objects and instead rested and groomed himself. The enriched environment produced cerebral changes in a single rat only if the rat was stimulated to interact with the objects
-Since brain plasticity is assumed to follow the same pattern in both animals and humans, the implications of the study are that the human brain should also be affected by environmental factors such as intellectual and social stimulation. It is now known that poverty is a major risk factor in children's cognitive development as poverty is related to a number of risk factors such as poor nutrition, lack of access to good education and poor health
-Highly controlled lab experiment
-Has been replicated several times
-Used animals, so it may not be able to be generalized to humans
-In the enriched environment, it could have been exercise that made a difference, rather than "stimulation." It is still not clear from the enriched environment how the variables of social interaction, environmental stimulation and exercise may interact
-There is the ethical consideration of undue stress or harm to the animals in the study. Not only were some rats isolated and put into an impoverished environment, but they were killed at the end of the study. A cost-benefit analysis should demonstrate that the goals of the study are worth the harm done to the animals.
Draganski et al (2004)
-Aim: To find out whether the human brain can really change structure in response to environmental demands
-Method: Researchers used a random sampling design and a self-selected sample. They randomly allocated volunteers into one of two groups: jugglers and non-jugglers. They made sure that the groups had no experience of juggling before the start of the experiment. Whole brain MRI scans were performed before the start of the experiment. Participants in the juggler group then spent 3 months learning a classic juggling routine with 3 balls. Another brain MRI was performed. Participants spent another 3 months where they were instructed not to practice juggling. A third MRI scan was completed. The control group (non-jugglers) just lived their daily lives and had their brains scanned 3 times on the same schedule as the jugglers.
-Comparison of the brain scans in the 2 groups prior to the start of the experiment showed no differences in the brain structure.
-Comparison of the second scans showed the juggler group had significantly more greymatter in some areas of the cortex - most notably the mid-temporal area in both hemispheres (areas associated with coordination and movement)
-The third scan showed a decrease in the differences between the two groups, but the amount of grey matter in these areas in jugglers was still greater than at the time of the first scan.
-Also there was a correlation between juggling performance and the amount of change: brain changes in participants who trained better were more pronounced.
-Random allocation of groups
-Low ecological validity
-Lacks internal validity (no changes in the coordination part of the brain)
-Lack of generalizability due to the small population and only the effect of learning juggling was measured.
Maguire et al (2000)
-Aim: To see whether the brains of London taxi drivers would be somehow different as a result of the exceptional training they have to do to be certified.
-Method: The participants of the study were 16 right handed male London taxi drives. The taxi drivers were compared with the MRI scans of 50 right handed males who did not drive taxis. In order to take part in the study, the participants had to have completed the "Knowledge" test and have their license for at least 1.5 years. The controls were taken from an MRI database. The sample included a range of ages so that age would not be a confounding variable. The study is correlational in nature as the IV is not manipulated by the researcher. The researchers were looking to see if there was a relationship between the number of years of driving a taxii and the anatomy of one's brain. It was also a single blind study(the researcher did not know whether she was looking at the scan of a taxi-driver or a control. The data from the MRI was measured using two different techniques: vowel-based morphometry (VMB) and pixel counting. Voxel-based morphology (VMB) was used in this study to measure the density of grey matter in the brain. Pixel-counting consists of counting the pixels in the images provided by the MRI scans in order to calculate the area of the hippocampus.
-Pixel counting revealed that the posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects and the anterior hippocampus were significantly smaller. VBM showed that the volume of the right posterior hippocampus correlated with the amount of time spent as a taxi driver. No differences were observed in other parts of the brain. Maguire argues that this demonstrates that the hippocampus may change in response to environmental demands.
-How does this relate to localization of function? It appears that the posterior hippocampus is involved when previously learned spatial information is used, whereas the anterior hippocampal region may be more involved during the encoding of new environmental layouts.
-A single blind control was used to avoid researcher bias
-Ethics (no health risks to the participants and all gave consent)
-You cannot argue that the MRI has low ecological validity because the participants were not asked to do anything while in the scanner. They simply had their brain anatomy measured
-Quasi experiment (No cause and effect relationship can be established)
-May not be able to be generalized because only males were used
Bremner et al (2003)
-Aim: To measure both hippocampal structure and function in women with and without early childhood sexual abuse and the diagnosis of posttraumatic stress disorder (PTSD)
-Method: 33 women participated in this study, including women with early childhood sexual abuse and PTSD (N=10), women with abuse without PTSD (N=12) and women without abuse or PTSD (N=11). The researchers used an MRI to measure the volume of the hippocampus in all of the participants, and a PET scan to measure its level of function during a verbal declarative memory test.
-A failure of hippocampal activation and 16% smaller volume of the hippocampus were seen in women with abuse and PTSD compared to women with abuse and without PTSD.
-Women with abuse and PTSD had a 19% smaller hippocampal volume relative to women without abuse or PTSD.
-These results are consistent with deficits in hippocampal function and structure in abuse-related PTSD.
-A control group was used
-Method triangulation was used
-High ecological validity
-Does not account for men
-Small sample size
-Other factors may have contributed to their hippocampal volume
Carrion et al (2009)
-Aim: To investigate the function of the hippocampus in adolescents with post-traumatic stress symptoms during a memory processing task
-Method: 27 adolescents between the ages of 10-17 years (16 with PTSS and 11 healthy controls) encoded and retrieved visually presented nouns (Verbal Declarative Memory Task) while undergoing fMRI scanning.
-The PTSS group demonstrated reduced activation of the right hippocampus during the retrieval component of the task. Further, severity of symptoms of avoidance and numbing correlated with reduced left hippocampal activation during retrieval.
-Decreased activity of the hippocampus during a verbal memory task may be a neurofunctional marker of PTSS in youth with history of interpersonal trauma.
-Not a brain imaging technique, but a way of measuring brain activity
-The product is a series of brainwave patterns that need to be interpreted
-Electroencephalography (EEG) is used to show brain activity under certain psychological states, such as alertness or sleep
-Also known as a CAT Scan
-A combination of x-rays and computer technology used to produce axial (like "slices") images of the brain
-It is used to assess head injuries and symptoms of aneurysm, stroke, and brain tumors
-Magnetic Resonance Imaging
-Create images of the structure of the brain
-The human body is made mostly of water. Water molecules contain hydrogen protons, which become aligned in a magnetic field. An MRI scanner applies a very strong magnetic field which aligns the proton "spins". The scanner also produces a radio frequency current that creates a varying magnetic field. The protons absorb the energy from the magnetic field and flip their spins. When the field is turned off, the protons gradually return to their normal spin, a process called precession. The return process produces a radio signal that can be measured by receivers in the scanner and made into an image.
-The MRI is a composite image of several images of the brain.
-Positron Emission Tomography
-Shows brain processes by using the sugar glucose in the brain to illustrate where neurons are firing.
-To do this, a radioactive isotope is injected into the bloodstream.
-This is an invasive technique.
-Functional Magnetic Resonance Imaging
-Scans are a series of MRI's measuring brain function via a computer's combination of multiple images taken less than a second apart.
-The images show activity in the brain over time.
-Single Photon Emission Computed Tomography
-Primarily used to view how blood flows through arteries and veins in the brain
-Tests have shown that it might be more sensitive to brain injury than either MRI or CT scanning because it can detect reduced blood flow to injured sites.
-A small amount of radioactive drug is injected into a vein and a scanner is used to make detailed images of areas inside the body where the radioactive material is taken up by the cells
-SPECT can give information about blood flow to tissues and chemical reactions (metabolism) in the body.
-Diffusion-Weighted Magnetic Resonance Imaging
-Measures the direction that water moves throughout the brain
-The connections between the neurons are made by the neurons' axons, which often travel together in bundles, sort of like a neural highway
-These bundles constrain the movement of water in the brain so that the water tends to move along the bundles trajectory, not through the bundle itself.
-Since dMRI measures water flow in the brain,we can use it to infer orientation of neural fiber bundles.
Strengths and Limitations of MRI and fMRI
-MRI's are non-invasive, unlike the PET scan.
-They are less expensive than PET and better temporal resolution. This means that the image is taken several times and then made into a composite image. The composite image is often lacking in precision and clarity, but is better than the PET scan.
-The MRI is a static image that does not demonstrate activity. Research is therefore correlational. Causation cannot be established.
-Although cheaper and safer than PET scans, the MRI's are still expensive. This means that sample size for research is often small. This makes it difficult to generalize the findings.
-Researchers can carry out limited experiments in an fMRI which allow for cause and effect relationships to be established.
-The fMRI is an artificial environment which means that experiments carried out in the fMRI lack ecological validity. As the MRI is only taking a picture of the static brain, ecological validity is not a concern.
-Artefacts can affect the "findings" of a brain scan. Artefacts can be activity in the brain as a result of something else besides what is being investigated. It can also be from the machine itself.
-The fMRI allows for researcher triangulation
-When used for research, there is the ethical problem of informed consent. Researchers may find a tumor or some other abnormality; it would be required for the researcher to inform the participant about any such findings
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