Methods of Cognitive Neuroscience

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Methods of Cognitive Neuroscience. Lesion Studies. Logic of Lesion Studies: damaged area plays a role in accomplishing whatever task is deficient after the lesion. Lesion Studies. Types of Lesions Animal Human. Lesion Studies. Animal Lesion Techniques Aspiration Lesions - PowerPoint PPT Presentation

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Methods of Cognitive Neuroscience

Methods of Cognitive Neuroscience

2Figure 4.16a Vascular disorders. Strokes occur when blood flow to the brain is disrupted. This brain is from a person who had an occlusion of the middle cerebral artery. The person survived the stroke. After death later, postmortem analysis showed that almost all of the tissue supplied by this artery had died and been absorbed.

3Figure 4.16b Vascular disorders. This brain is from a person who died following a cerebral hemorrhage. The hemorrhage destroyed the dorsomedial region of the left hemisphere. The effects of a cerebrovascular accident 2 years prior to death can be seen in the temporal region of the right hemisphere.

4Figure 4.17a Postmortem views of three types of brain tumors.A malignant glioma infiltrated the white matter of the parietal lobe in the right hemisphere in this case.

5Figure 4.17b Postmortem views of three types of brain tumors. Here a large meningioma led to massive compression of the right frontal lobe. This patient had been hospitalized at age 41 for psychotic behavior, quite likely due to the effects of this slow-growing tumor. The tumor was not detected until autopsy.

6Figure 4.17c Postmortem views of three types of brain tumors. A metastatic tumor is seen here in the dorsomedial tip of the left hemisphere. This woman died 5 years after undergoing a mastectomy for breast cancer.

7Table 4.1 Prominent Degenerative and Infectious Disorders of the Central Nervous System

8Figure 4.18a Degenerative disorders of the brain. This coronal section is from a patient with Alzheimers disease who died at age 67, 8 years after the first reports of memory problems. Severe cortical atrophy is apparent; at death, her brain weighed only 750 g, less than half the weight of a normal brain.

9Figure 4.18b Degenerative disorders of the brain. In this brain from a patient who died of Picks disease, the atrophy is limited to frontal and temporal lobe regions.

10Figure 4.18c Degenerative disorders of the brain. These transverse MRI scans from a patient with Alzheimers disease show that atrophy has led to enlargement of the sulci and ventricles.

11Figure 4.19a Trauma can cause extensive destruction of neural tissue. Damage can arise from the collision of the brain with the solid internal surface of the skull, especially along the jagged surface over the orbital region. In addition, accelerative forces created by the impact can cause extensive shearing of dendritic arbors. In this brain of a 54-year-old man who had sustained a severe head injury 24 years prior to death, tissue damage is evident in the orbitofrontal regions and was associated with intellectual deterioration subsequent to the injury.

12Figure 4.19b The susceptibility of the orbitofrontal region to trauma was made clear by A. Holbourn of Oxford in 1943, who filled a skull with gelatin and then violently rotated the skull. Although most of the brain retains its smooth appearance, the orbitofrontal region has been chewed up.

Lesion StudiesLogic of Lesion Studies:damaged area plays a role in accomplishing whatever task is deficient after the lesionLesion StudiesTypes of LesionsAnimalHuman

15Page 123 The morality of using animals for research purposes has been debated for centuries. People on both sides of the debate have recognized the importance of engaging the publica point underscored by the fact that members of the U.S. Congress receive more letters on this issue than on any other.Lesion StudiesAnimal Lesion TechniquesAspiration LesionsElectrolytic Lesions

Lesion StudiesAnimal Lesion TechniquesAspiration LesionsElectrolytic Lesions

Problems:These can damage surrounding tissue - especially white matter tracts nearby (fibers of passage)

Irreversible

eventual degradation of connected areas

Lesion StudiesAnimal Lesion TechniquesVascular Lesionsendothelin-1good model of human strokesevere damagenot pinpoint accuracy

Lesion StudiesAnimal Lesion TechniquesReversible LesionscoolingLocal anesthetic, other drugshighly selectivecan cool specific layers of cortexcan be reversed!

Lesion StudiesAnimal Lesion TechniquesSelective Pharmacological lesionsdamage or destroy entire pathways that have a specific sensitivity to a particular chemical

e.g. MPTP model of Parkinsons Disease (frozen addicts)e.g. scapolomine - acetylcholine antagonist - temporary amnesia

Can be selective for specific circuits but not for specific brain areascan be reversible in some cases (e.g. scopolamine, but not MPTP)

Lesion StudiesAnimal Lesion TechniquesGene Knock-Out/Knock-In (Transgenics)can selectively block/enhance expressionViral vectors, electroporationanimal develops differently

Can have temporal/regional/molecular specificity

Lesion StudiesHuman LesionsIschemic EventsStroke and Hemorrhage:typically due to blood clot or hemorrhagesize of lesion depends on where clot gets lodgedamount of damage depends on how long clot remains lodged Lesion StudiesHuman LesionsTraumaFrontal lobes are particularly susceptibleSome famous cases (e.g. Phineas Gage) Lesion StudiesHuman LesionsSurgeryOften surgery done to treat epilepsyOccasionally corpus callosum is severed

Problem: patient wasnt normal before the surgeryLesion StudiesHuman LesionsTranscranial Magnetic StimulationElectromagnet Induces current in the brainvery transient, very focal reversible lesion

Believed to be safesites that can be studied are limited by the geometry of the head

26Figure 4.25b Transcranial magnetic stimulation. Here the TMS coil is being applied by an experimenter. Both the coil and the subject have affixed to them a tracking device to monitor the head/coil position in real time.

27Figure 4.25c Transcranial magnetic stimulation. The subjects MRI can be used along with the tracking system to display the cortical area being targeted.

28Figure 4.25d Transcranial magnetic stimulation. The TMS pulse directly alters neural activity in a spherical area of approximately 1 cm3.

29Figure 4.26a Transcranial magnetic stimulation over the occipital lobe. The center of the figure-eight coil is placed over the targeted area. When a large electrical field is passed through the coil, a magnetic pulse is generated and passes through the skull. This pulse activates neurons in the underlying cortex.

30Figure 4.26b Transcranial magnetic stimulation over the occipital lobe. The time between the onset of the letter stimulus and the pulse varies. When the pulse follows the stimulus by 70 to 130 ms, the subject fails to identify the stimulus on all trials. Note the failures when the pulse precedes the letter. These occur because the subject briefly blinks on some trials after the pulse.

Lesion StudiesMaking sense of Lesion studiesLesion StudiesLogic of Lesion Studies:damaged area plays a role in accomplishing whatever task is deficient after the lesionWarning:This isnt the same as saying the lesioned area does the operation in questionexamples:normal behaviour may be altered to accommodate lesione.g. sensory loss of one arm favors other armlesion might cause upstream problem or general deficite.g. attention problem looks like specific deficit if you only test one specific demanding task

Lesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

First, use a control condition

PerformanceTaskALesion XLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

First, use a control condition

PerformanceTaskALesion XHealthyLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

First, use a control condition

PerformanceTaskALesion XHealthyThis difference indicates deficit Lesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

But maybe this is a general deficit! - use 2nd task

PerformanceTaskALesion XHealthyThis difference indicates deficit Lesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

But maybe this is a general deficit! - use 2nd task

PerformanceTaskALesion XHealthyBLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

But maybe this is a general deficit! - use 2nd task

PerformanceTaskALesion XHealthyBindicates that deficit is selectiveLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

This result is called a single dissociation

PerformanceTaskALesion XHealthyBindicates that deficit is selectiveLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

What if Task A is just harder than B? - add a 2nd group

PerformanceTaskALesion XHealthyBLesion YLesion StudiesDesigning Lesion Studiesdesign tasks that diagnose the function of specific operations

This result is a double dissociation

PerformanceTaskALesion XHealthyBLesion YInteraction suggests two lesions have specific and independent deficits

42Figure 4.22 Hypothetical series of results conforming to either a single (a) or a double (b) dissociation. With the single dissociation, the patient group shows impairment on one task and not on the other. With the double dissociation, one patient group shows impairment on one task and a second patient group shows impairment on the other task. Double dissociations provide much stronger evidence for a selective impairment.

43Figure 4.22a Hypothetical series of results conforming to either a single (a) or a double (b) dissociation. With the single dissoc

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