Week 5 - topic 1 Flashcards
1
Q
Lesion studies
A
- Experimental Ablation is the removal or destruction of a portion of the brain of a laboratory animal. Presumably, the removal of a portion of the brain will influence neural functioning, and thus, behaviour.
- A lesion is a wound or injury. Thus, a brain lesion specifically refers to a wound or injury of the brain.
- Experiments in which a part of the brain is damaged, and behaviour is subsequently observed are called lesion studies.
2
Q
Lesion studies can include
A
- Animals that have had parts of their brain intentionally removed/damaged.
- The study of patients who have experienced a lesion due to some accident or stroke. For example, you have probably heard of Phineas Gage, who, after a railroad accident, had an extreme change in personality.
- > Experiments in which a part of the brain is damaged, and behaviour is subsequently observed are called lesion studies
3
Q
Why do we have lesion studies
A
- The key assumption underlying lesion studies is that the function of a particular area of the brain can be inferred, by observing changes in behaviour after the area has been damaged.
- Thus, the goal of the lesion approach is to discover what functions are performed by different regions of the brain, and then to understand how these functions are combined to produce particular behaviours
4
Q
Inferences from the results of lesion studies
A
- For example, reading (a behaviour) involves functions for controlling eye movements, perceiving and recognizing words and letters etc. We can use the lesion approach to understand what functions (e.g. eye movements or comprehension) are impaired following a lesion which has lead to the specific behavioural changes (e.g. reading impairment).
- It is important to note that the findings of lesion studies can be somewhat difficult to interpret because all regions of the brain are interconnected. That is, there is not just one area that is responsible for all of vision, another for language, and another for personality etc
5
Q
Patient HM
A
- bicycle accident left him with severe seizures (epilepsy). - at 26 he was operated on, the left and right medial temporal lobes which include the structures hippocampus, amygdala and part of the entorhinal cortex were removed
- HM long term memory formation was impaired after surgery, but he could remember his name and childhood
- he could not learn the names of new people, but his ability to implicitly learn new skills was still in tact - he knew his way to the hospital dining room.
These lesions helped understand the functions of the hippocampus and amygdala in memory formation. It helped clarify the connections and differences between different types of memory.
6
Q
Patient Tan
A
- Tan was an individual with language difficulties. Despite being able to understand and follow commands, the only word he could say was “Tan”.
- Broca performed an autopsy on Tan and found a lesion on the left frontal lobe of his left cerebral hemisphere, just above his left eye. This area is now known as “Broca’s area”.
- The condition of Tan was named aphasia (the inability to produce words that were meaningful, but being able to understand language perfectly). This case study taught us alot about Broca’s area being associated with language production
7
Q
Patient Phineas Gage
A
- Phineas Gage was a construction worker who set off an explosion that sent an iron rod shooting through his cheek and head. He didn’t die, but he wasn’t the same.
- He had a complete personality change, lost his job, would swear alot, and was irritable.
- He experienced damage to his frontal lobe, and was highly influential in the progression of ideas around brain-mind connections.
- > Perhaps functions related to personality are associated with this region of the brain
8
Q
Radio frequency lesion
A
- Electrical current is passed through a stainless steel wire (electrode)
- Researchers guide the electrode to a very specific location in the brain
- Activate a lesion making device that produces an alternating current of very high frequency - a radio frequency
- Passing current through brain tissue produces heat that kills cells surrounding the tip of the electrode
9
Q
Excitotoxic lesion
A
- Excitatory amino acid is injected via a cannula into a brain region.
- The amino acid kills neuron cell bodies by stimulating them to death
- Axons nearby are spared = selectivity
10
Q
Sham lesions
A
- a placebo procedure that duplicates the steps of producing a brain lesion except for the final step of actually damaging the cells
- If you put an electrode or cannula deep into the brain, you are going to damage some tissue along the way.
Therefore, sham lesions are also produced.
-> Researchers insert an electrode or a cannula into the brain region of an animal, but do not activate the RF current, or inject the amino acid.
11
Q
Temporary brain lesions
A
Brain lesions can also be made temporarily:
Example:
Inject a local anesthetic into the part of the brain you want to lesion.
The anesthetic blocks action potentials in axons entering or leaving to produce a temporary lesion.
12
Q
3 types of non-invasive brain structure imaging
A
Computerised tomography (CT)
Magnetic Resonance Imaging (MRI)
Diffusion Tensor Imaging (DTI)
13
Q
Computerised tomography (CT)
A
The use of a device that employs a computer to analyse data obtained by a scanning a beam of X-rays to produce a two-dimensional picture of a “slice” through the body.
- medium resolution pictures
- useful for finding strokes, tumours and atrophy of the brain
14
Q
Magnetic Resonance Imaging (MRI)
A
- A technique whereby the interior of the body can be accurately imaged; involves the interaction between radio waves and a strong magnetic field
- A powerful computer compiles the density based information to generate a detailed cross sectional view of the brain
- useful in Alzheimers studies
15
Q
Diffusion Tensor Imaging (DTI)
A
- An imaging method that uses a modified MRI scanner to reveal bundles of myelinated axons in the living human brain.
- The MRI scanner uses information about the movement of the water molecules to determine the location and orientation of bundles of axons in white matter.
- useful for studies of schizophrenia and PTSD
