The Lesion Method:
Neuroimaging Techniques:
examine the effect of brain damage on cognitive function or interfere with cognitive function artificially through TMS (create temporary lesions in small region of cortex)
use measures of brain activity as “markers” of different cognitive processes
H.M
K.F
– surgery of epilepsy
– removal of medial portions of temporal lobes (inc. HC)
– HC is critical for encoding new episodic memories
– unable to form new LTM
– digit span is intact (6 digits)
– verbal STM intact
– LTM is intact
– STM is impaired
– digit span is only 1
Ivory
Semantic Dementia
- severe knowledge difficulties
- recall of past events is intact
- remembers rules for games
e.g., when shown a picture of a dog, calls it a cat.
Semantic Dementia
difficulty…
What does this tell us about the processes involved reading words?
reading irregular words
need to access knowledge about the words to identify irregular words
M.H – damage to... – difficulty... – older and recent recollections... – unable to draw familiar objects from memory... – unable to visually... – lost the capacity to...
occipital lobes recalling past experiences devoid of visual information despite good knowledge of objects recall information (loss of visualisation) mentally visualise past events
Voxel-Based Lesion-Symptom Mapping
voxel =
perform analysis at each voxel to work out…
alexithymia =
brain damage in these voxels (mPF and AC and lPF) is associated with…
- smallest distinct unit visible on MRI image
- code every part of image as single voxel
which voxels – when damaged – impacts on behaviour measure
a construct that a person can’t understand what emotions they feel
poorer scores on the Toronto Alexithymia Scale (= poor emotional awareness)
Studying Brain Damage – Advantages
- learn more than…
- learn how a certain skill….
- learn how an ability….
- learn what regions are…
where things happen in the brain
or function operates
contributes to functioning and experiences
active and crucial during a task
Studying Brain Damage – Limitations
- brain damage is…
- brain damage is…
- patients may learn…
- no two patients have…
rare - some regions are rarely selectively damaged, fewer cases to study
not random - some patients are unusual premorbid (= prior to illness)
to compensate - learn to use alternative strategy (e.g., prosopagnosia: learn to recognise people using voice cues, hairline shapes and neural plasticity: reallocation of damaged cortex to new function)
exactly the same damage - averaging across multiple patients can obscure differences
Transcranial Magnetic Stimulation (TMS)
- high powered…
- delivers…
- interferes temporarily with…
- can induce a temporary…
- TMS is another way of applying…
- TMS is a magnet with…
- It has a…
- observe impacts on different behaviours when…
Pobric, Jefferies & Lambon Ralph (2007):
o whether anterior left temporal lobe was critical for…
o participants named pictures or numbers
o rTMS slowed processes for…
o limitation of TMS is that it has…
magnet magnetic pulse to the brain cognitive processing in targeted region localised “lesion” in healthy subjects the lesion method strong magnetic field that interferes with the electrical signals in the area of the brain local effect (does not penetrate into brain more than one cm) stimulating different parts of brain
generating names
picture naming and no effect on number naming
a small effect
Transcranial Magnetic Stimulation (TMS):
- can randomly select participants…
- can stimulate regions…
- can compare each participant to…
Limitations:
- only cm within…
- issues with stimulating…
- TMS does not produce massive…
- powerful effects when stimulating…
from population (overcomes problem of premorbid differences)
not damaged
themselves (e.g., with vs without TMS, or TMS to two different regions)
cortex (deep inside white matter)
ventral surface of brain (face and word recognition regions)
dysfunctions – no extreme effects for cognitive areas
motor areas
Functional Neuroimaging
examines markers of…
1. electrophysiological: examine…
2. metabolic: examine changes in…
brain activity during a cognitive task
electrical changes occurring when large groups of neurons fire at same time (ERP, MEG)
blood during mental activity. Active brain regions take up more oxygen from the blood (fMRI, PET)
Metabolic Methods PET: - maps uptake of a... - poor temporal... - more sensitive than...
fMRI:
- measures magnetic…
- non-invasive
- good temporal…
(note: these techniques have great spatial resolution)
radioactively tagged substance (e.g., oxygen, glucose)
resolution (need to use blocked designs)
fMRI for some brain regions (e.g., temporal pole, inferior temporal lobe, orbitofrontal cortex).
changes in blood as it deoxygenates
resolution (1–2secs) – can use event-related designs
Neuroimaging Techniques
e.g., neural correlates of the aha! moment
– participants solve problems (view 3 words, think of word related to them)
– areas activated when ‘aha’ moment minus areas activated when no ‘aha’ experience (subtraction design)
– result? more areas engaged…
when ‘aha’ moment
Advantages over traditional measures
- different mental processes may be…
- can infer what processes are…
spatially distinct – helps tease them apart
engaged by the areas activated
Advantages over lesion method
- can examine all structures that are…
- can look at timing of…
- can study the role of structures that are…
active during a task
various processes, and the way different regions interact
rarely damaged and/or inaccessible to TMS (anterior cingulate)
What can and can’t we learn using fMRI
e.g., neurological basis for lack of empathy in psychopaths
– participants viewed images of bodily injuries
– participants imagined it was: (a) them; or (b) someone else
– those with high psychopathy scores, amygdala was..
– in right amygdala psychopaths were…
fMRI measures activity, it does not…
not activated for “someone else”
reduced in activation compared to non-psychopaths, when imagining other person, inability to feel emotion for others
establish cause, another measure of behaviour
Functional Neuroimaging Limitations
- not clear which regions are…
- need to make a number of…
- inferring what is going on by…
- without careful cognitive theorising, results will be…
- only examines…
doing the important work
assumptions during task design (e.g., subtraction)
the location of activation alone can be shaky
meaningless
active regions during task, not crucial regions (lesion tasks do)
