the lesioned brain Flashcards
What is TMS?
Transcranial Magnetic Stimulation
means of disrupting normal brain activity by introducing neural noise - ‘virtual lesion’
how does TMS work?
- TMS coil current
- magnetic field pulse
- rate of change of magnetic field
- induced electric field
- induced tissue current
TMS- Faraday’s coil
if apply current of electricity through one side of coil, will generate a magnetic field
if varies enough, can generate current in another part of the coil
What is the aim of TMS studies?
applying a pulse at any cortical node of the neural network will interfere with the relevant neural signal
efficacy of neural signal is degraded
observe change in behaviour
what are the advantages of TMS?
- interference/virtual lesion technique
- transient and reversible
- control location of stimulation
- establishes causal link of different brain areas and a behavioural task
what is language lateralisation?
language is a function of the left side of brain (generally)
comparing left and right language dominant people
given semantic task, then TMS
when you stimulate the dominant side, that side is inhibited
so therefore it cannot inhibit the actions of the opposite side
What is TES?
Transcranial electric stimulation
produces weak current applied via scalp electrodes to specific brain regions
promising results in therapy
what are the different protocols for TES?
tDCS: transcranial direct current stimulation
tACS: transcranial alternating current stimulation
tRNS: transcranial random noise stimulation
effect of repeated stimulation of tDCS
lead to changes in neuronal excitability that outlast the stimulation itself
clinical application
TES protocols - tDCS
- anodal: facilitation effects
- cathodal: inhibition effects
- Sham (control): 30s stimulation
how do neurotransmitters work in tDCS?
anodal stimulation inhibits GABA (inhibitory neuro.)
cathodal stimulation inhibits glutamate (excitatory neuro.)
tACS
uses low level alternating currents applied via scalp electrodes to specific brain regions
what is the rationale behind tACS?
entrainment (synchronisation) of internal brain rhythms with externally applied oscillating electric fields
oscillatory fields cause phase-locking of large pool of neurons –>
increases of neural synchronisation at corresponding frequency
what is lucid dreaming?
an overlap between two states of consciousness
one in dreaming, one in wakefulness
transfer elements of waking consciousness into the dream
Voss et al: lucid dreaming
EEG for 27 ps, applied tACS
LuCID scale to report dreams
how is lucid dreaming shown shown in EEG?
overlap of states is reflected in brain waves.
shows in gamma waves in frontal cortex, an activity pattern that is linked to consciousness but is nearly absent during sleep and normal dreaming
Voss et al: results
brain’s gamma activity increased during stimulation with 40Hz, and lesser degree with 25Hz
insight and dissociation (control over plot only with 25Hz)
both TMS and TES can cause…
after-effects on excitability of neurons and networks that outlast stimulation by mins/hrs
TMS and TES combined with behavioural training…
can offer promising alts to pharmacological interventions and can enhance cognitive performance
what is Neuropsychology and what traditions?
studying brain damaged patients - gives insight into formal function
classical neuropsychology and cognitive neuropsychology
what is classical neuropsychology?
what functions are disrupted by damage to region x?
Addresses questions of functional specialization, converging evidence to
functional imaging
Tends to use group study methods
what is cognitive neuropsychology
Can a particular function be spared/impaired relative to other cognitive functions?
Addresses questions of what the building blocks of cognition are (irrespective of
where they are)
Tends to use single case methodology
forms of brain damage
Cerebrovascular accident (CVA or stroke)
Neurosurgery (split brain)
Viral infections (HSE, HIV)
Tumour (glioma)
Head injury (traffic accidents, rugby)
Neurodegenerative disease (Dementias: Alzheimer type)
what is a stroke and what are the 2 types?
loss of brain function after disturbance of blood supply
Ischemia and haemorrhage
What is ischemia?
blood clot stops flow of blood to area of brain (lack of glucose and oxygen supply)
what is a haemorrhage?
weakened blood vessels rupture and leak into brain tissue (bleeding into brain tissue)
what is the aim of neuropsychological testing?
Assess what they can do after having a stroke:
semantic memory: pyramids and palm trees/pine tree, which one is related?
visuospatial testing: figure of ray - draw from memory
what is a single dissociation?
If a patient is impaired on a particular task (Task A), but relatively spared on another task (Task B)
what is a classical single dissociation?
If patient performs within the normal range on the Task B (spared task)
what is a strong single dissociation?
If patient is impaired on both tasks, but is significantly more impaired on one task
Patient CF
classical single dissociation
at time of stroke, was completely speechless but could communicate through gestures
writing: systematically omitted vowels
(another patient made errors on only consonants)
what does Patient CF tell us about cognitive neuropsychology?
behind these single dissociations is that a difficulty in one domain,
relative to an absence in difficulty in another domain can be used to infer the
independence of these domains
comparing 2 patients: conclude that brain has separate neural resources for processing vowels and consonants
what is a double dissociation?
derived from 2 single cases with complementary profiles:
lesion of brain area A impairs function 1 but not function 2, while a lesion of brain area B produces the reverse pattern
eg. Broca’s aphasia and Wernicke’s aphasia
what are the issues with single case studies?
one can not average observations from
single studies because each patient may have
a different cognitive lesion that we can not know
a priori
how are group studies grouped?
by syndrome
by behavioural symptoms
by lesion location
grouping studies by syndrome
useful for investigating neural correlates of a disease
pathology (e.g. Alzheimer’s) but not for dissecting cognitive theory
grouping studies by behavioural symptoms
Can potentially identify multiple regions
that are implicated in a behaviour
grouping studies. by lesion location
Useful for testing predictions derived from
functional imaging
what are 3 methods for studying the lesioned brain?
TMS
tDCS
Neuropsychology
