Week 5 - topic 1

Question 1

Lesion studies

Answer 1

• 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.

Question 2

Lesion studies can include

Answer 2

• 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

Question 3

Why do we have lesion studies

Answer 3

• 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

Question 4

Inferences from the results of lesion studies

Answer 4

• 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

Question 5

Patient HM

Answer 5

• 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.

Question 6

Patient Tan

Answer 6

• 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

Question 7

Patient Phineas Gage

Answer 7

• 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

Question 8

Radio frequency lesion

Answer 8

• 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

Question 9

Excitotoxic lesion

Answer 9

• 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

Question 10

Sham lesions

Answer 10

• 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.

Question 11

Temporary brain lesions

Answer 11

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.

Question 12

3 types of non-invasive brain structure imaging

Answer 12

Computerised tomography (CT)
Magnetic Resonance Imaging (MRI)
Diffusion Tensor Imaging (DTI)

Question 13

Computerised tomography (CT)

Answer 13

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

Question 14

Magnetic Resonance Imaging (MRI)

Answer 14

• 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

Question 15

Diffusion Tensor Imaging (DTI)

Answer 15

• 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

Question 16

Process of an MRI

Answer 16

• Head placed in a powerful magnet. The magnet causes protons in the brain tissue to line up in parallel (normally they are in random orientations).
• Protons are knocked over by a powerful pulse of radio waves -> When the pulse is turned off, the protons go back to their original configuration, emitting radio waves as they do.
• Scanner picks up the radio frequency energy being emitted -> The energy emitted differs for tissues of varying densities

Question 17

How DTI works

Answer 17

• Molecules move in random directions because of thermal agitation, and the higher the temperature, the faster the movement.
• DTI takes advantage of this.
• Movement of water molecules in bundles of white matter will not be random, but will tend to be in a direction parallel to the axons that make up the bundles.