Chapter 5 Flashcards
Mind and the lesioned brain: classical cases
Tan = language
Phineas Gage = personality
DF = object recognition
HM = memory
Reverse engineering
Infer the function of a region (or cognitive mechanism) by removing it and measuring the effects on the rest of the system (e.g. if damage to a region disrupts reading, but not speaking or seeing, than one might conclude that the region is specialized for some aspect of processing text).
How does disruption of the brain happen?
(1) Natural damage (stroke, trauma), (2) elicited damage (animal models) or (3) harmless temporary changes induced electro-mechanically (TMS).
Neurosurgery
Brain is damaged deliberately.
Cerebrovascular accident (CVA)
Accident of the arteries (vascular) of the brain (cerebro). There are two types: (1) Ischemic infarction (80%) = herseninfarct/beroerte, (2) Hemorrhage or bleeding (20%) = hersenbloeding.
Traumatic brain injury
Various mechanical forces can result in: (1) Open traumatic brain injury (more localized), (2) closed traumatic brain injury (more widespread effects).
Single dissociation
A patient is impaired on task A but (relatively) spaired on task B; classical versus strong dissociation.
What inferences can be drawn from single dissociation?
(1) Task A and B rely on different cognitive processes, (2) task-demand artifact (supoptimal performance; misunderstanding), (3) task-resource artifact (same resources, but more needed for task A).
Double dissociation
Normally derived from 2 or more single cases with complementary profiles of strengths and weaknesses; used to infer that two tasks/stimuli use separate neural/cognitive resources.
Intracranial tumors
Mass of new tissue that persists and grows independently; classification: (1) benign versus malignant, (2) encapsulated versus infiltrating, (3) primary versus secondary, (4) cell types (meninges versus glia).
Viral infections
Invasion of the body by disease-producing microorganisms and subsequent tissue reactions.
How do infections kill neural cells?
(1) They interfere with blood supply, (2) they disturb glucose of oxygen metabolism, (3) they alter cell membranes, (4) they cause edema (5) they form pus.
Associations
Patient is impaired on task A and task B. Perhaps functions are close together in the brain?
Syndromes
a cluster of different symptoms that are believed to be related in some meaningful way (e.g. Gerstmann syndrome).
Two traditions of human neuropsychology
(1) Cognitive neuropsychological approach: can a particular function be spared/impaired relative to other cognitive functions; adresses questions of what the building block of cognition are (irrespectable of where they are); tends to use single case methodology, (2) Classical neuropsychology approach: What functions are disrupted by damage to region X; adresses questions of functional specialization, converging evidence to functional imaging; tends to use groups study methods.
Assumptions underlying single case studies
(1) Fractation assumption: damage to the brain can selectively impair a cognitive function, (2) transparency assumption: other cognitive functions at normal pre-injury levels of efficiency, (3) universality assumption: all individuals share the same cognitive systems.
Group studies and lesion-deficit associations
(1) Group by syndrome = useful for investigating neural correlates of a disease pathology (e.g. Alzheimer’s) but not for dissecting cognitive theory, (2) group by behavioral symptom = can potentially identify multiple regions that are implicated in a behavior, (3) group by lesion location = useful for testing predictions derived from functional imaging.
Issues related to patient grouping
(1) Some forms of brain damage (e.g. tumors, swelling/edema) make it hard to localize the lesion, (2) diaschisis: brain damage can induce functional lesions at a distance (e.g. when regions function as a network), (3) danger in concluding that a function is localized in a region, or the purpose of that region is to support that function (neophrenology), (4) one needs to consider whether the region performs other functions and if other regions support this function.
Advantage single case studies
Can be important to determine what the components of cognitive systems are.
Advantage group studies
Can be important for establishing whether a given region is critical for performing a given task.
TMS
A coil contains a wire carrying an electrical current, a rapid change in the current creates a magnetic field, the magnetic field induces a current in the nearby neurons (causing them to fire, i.e. generate action potentials, this disrupts cognitive function they may be doing at a certain point in time.
Advantage of TMS
No reorganization or compensation, can be used to determine timing of cognition, lesion is focal, lesion can be moved within the same participant, can study functional integration.
Advantage of natural damage
Subcortical lesions can be studied, lesions can be accurately localized with MRI, changes in behavior/ cognition are more apparent, clinical relevance is obvious.
Brain stimulation to enhance brain function
Therapeutic effects of TMS and tES when repeated a lot, several promising areas of investigation: mood disorders that do not react to other treatments, obsessive compulsive disorder, revalidation after stroke.
NIBS
A name for a variety of methods that stimulate the brain noninvasively including by magnetic, electrical and ultrasound methods.
tES
Noninvasive stimulation of the brain caused by passing weak electrical current through it, either direct currents (tDCS) or alternating currents (tACS).
Split-brain
A surgical procedure in which fibers of the corpus callosum are severed.
Aneurysm
Over-elastic region of an artery that is prone to rupture.
Dysgraphia
Difficulties in spelling and writing.
Edema
A swelling of the brain following injury.
Diaschisis
A discrete brain lesion can disrupt the functioning of distant brain regions that are structurally intact.
Behavioral neuroscience
Cognitive neuroscience in non-human animals.
tDCS
Noninvasive stimulation of the brain caused by passing a weak electrical current through it.
tACS
Noninvasive stimulation of the brain caused by passing a weak alternating electrical current through it; the frequency of the alternations can interact with the brain’s own rhythmical activity.
tRNS
Noninvasive stimulation of the brain caused by passing a weak electrical current through it, which fluctuates in direction and amplitude.
