Methods for Studying the Brain :male-doctor::skin-tone-2: (Brain Activity,…
Methods for Studying the Brain :male-doctor::skin-tone-2:
Localist v anti-localist
(i) The brain is composed of specialised areas. (anatomical evidence)
(ii) Information processing in each of these is local and specific (brain activity studies)
(iii) Discrete areas are responsible for discrete functions (lesion studies)
i) The brain is a collection of networks (anatomical evidence)
(ii) information processing is ‘distributed’ (brain activity studies)
(iii) All areas are equally responsible for all functions (lesion studies)
e.g. Flouren's aggregate field theory - small lesions to birds
e.g. Lashley neurons perform all purposes - lesions in rats, size related to impairment not location
localised and distributed processing
aims of modern neuroscience
explain functional segregation and functional integration
Insufficiency of lesion studies
Lesions that impair functions
Essential info processing for the task takes place in that area.
Essential info processing in connected areas is disrupted.
Lesions that don’t impair functions
Information processing in that area is not needed for the task.
Information processing is needed for the task in the normal brain, but the lesioned brain compensates to restore function.
There are many interpretations to lesion studies so, they cannot tell us about why lesions do/don’t cause deficits.
Because these alternative explanations are all possibly true, we must study the intact brain.
Brain architecture: connectivity
Relationship between neural and cognitive processes
conventional tracer injected into neuron - reveals terminal sites
can't cross synaptic cleft, can't trace whole circuit
Info flow is integral part of info processing
GM, can cross synaptic cleft, reproduce during transmission so signal strength not affected by distance, clefts are labelled so whole circuit is traced
however, only viable in nonhumans
Diffusion Tensor Imaging
new MRI tech makes it possible to trace fibre pathways
something to do with water diffusion in a fibre bundle
Both human and macaque premotor coretex can be divided into cytoarchitectonically distinct subregions but determining these boundaries in vivo is challenging
high temporal, low spatial res
ERP's indicate how neural activity changes over time
high temporal, higher spatial because magnetic signal less distorted than EEG
MEG is much more expensive and
physically restrictive than EEG
PET scanners measures changes in blood flow that
are stimulated by changes in neural activity.
ok spatial, poor temporal, can image deep structures as well as cortex, indirect measure
high spatial, low temporal
Logothetis et al 2001 - BOLD signal
suggests that BOLD activation may actually reflect more the neural activity related to the input and the local processing in any given area, rather than the spiking activity commonly thought of as the output of the area
Both single- and multiunit responses adapt a couple of seconds after stimulus onset, with LFP remaining the only signal correlated with the BOLD response
Important in animal studies for determining exactly where the signal is coming from, at very high temporal spatial res
applied onto cortical areas, the induced current depolarizes nearby located neuron assemblies located beneath the coil and generates neurophysiological and/or behavioral effects depending on their contributing functions
can deliver disruption for a very small amount of time at a very localised area of cortex
can therefore target very specific processesthat occur in particular time points in experiments
Purpose: Stimulation of specific parts of the brain (e.g. specific areas within the basal ganglia) alleviate the symptoms of particular disorders
Method: Electrodes are implanted into specific subcortical areas and connected to implanted stimulators powered by battery
target basal ganglia to treat parkinson's
long-term effects of using highfrequency (130–185 Hz) DBS for Parkinson’s disease are well documented
have shown substantial improvements in symptoms, as measured by motor and daily living scores
What is the relationship between the BOLD signal and the
underlying neuronal activity?