W1L2 - Electrical signals in the brain Flashcards
What are the methods for Intracranial electrical recordings
Single cell animal studies
ECoG
What are the methods for Extracranial electrical recordings
EEG
ERP
What are the methods for Intracranial electrical stimulations
DCES
What are the methods for Extracranial electrical stimulations
tDCS
What is the history of intracellular and extracellular recordings
Intra: Recording of giant axon in squid
Extra: Single neurons in visual cortex of anasthetized cats
Extracellular Recordings of Single Neurons: Types
Anaethsized Studies: Sensory and Motor
Awake behaviour Studies: Higher level functions like attention
Mulitple neurons can be studied with electrode arrays
What is Local Field Potential. What is the pros and caveat.
Not related to individual neurons. Measures neural activity up to 3mm from the electrode
LFPs likely represents synaptic activity (summed activity of large numbers of neurones with synchronous input)
Caveat:
More likely to reflect type cells with dendrites facing in the same direction away from cell body (pyramidal cells)
ECoG overview. What is it used to clinically
2-256 electrodes in an array placed directly on the exposed surface of the brain : Records LFP
Used to treat epilepsy by identifying region generating seizures
DCES uses same electrode
ECoG pros
1.) High spatial and temporal resolution
2.) Both single/multi-unit recording
3,) Understanding how indirect methods like fMRI relate to direct neural responses
ECoG + BOLD Study. Results.
Siero et al. (2014): 7T fMRI prior to ECoG in finger flexion
- High frequency ECoG (65-95Hz) matches localised BOLD
- BOLD co-localises rapid neural changes at fine spatial scale
EEG Overview
Electrical activity measured depends on large no. of synchronous, aligned neurons
Usually recording pyramial neurons (best for cortical gyri not sulci)
EEG Pros
- ) Cheap
2. ) Good Temporal
EEG Cons
- ) Not good for deep structures
2. ) Poor spatial
How does EEG move to ERP
x1000 trials + signal averaging
DCES Overview
Stimulation of Single Neurons, mostly on awake behaving non-human primates
Same electrodes as ECoG
DCES Cons
Clinical patients limit the basic research
- Must have epilepsy
- No choice in electrode location (Gyrii + Seizure place)
- Surgery = Expensive
tDCS Overview and Aim
- Passing a weak DC current between electrodes placed on the scalp
- The aim is to stimulate the brain and improve mental function
tDCS vs other techniques
- ) Does not require medical intervention
- ) Uses DC to influence brain activity
- ) Uses weak current to influence brain activity
How does tDCS work
- Small current passed between two electrodes on the scalp.
- Assume that current flows though the brain
- Neurons under the anode more easily activated than they otherwise would be (Not direct activation)
Excitation: Anode
Inhibition: Cathode
tDCS problems
- ) Precise mechanisms elusive
2. ) Precise and selective stimulation of a target brain region difficult
tDCS pros
- ) Non invasive
- ) Cheap to purchase and use
- ) Easy to use
- ) Safe when using established protocols (straight forward ethics)
Does scientific evidence suggest tDCS is effective
No. Meta-analysis found no reliable effect.
Criticism of meta-analysis: Not enough studies and poor designs.
What are the difficulties in establishing whether tDCS is effective?
- ) High prevalence of “adverse” events = strong placebo
2. ) No active sham control
Has the rapid increase in studies contributed to the tDCS confusion?
High rates of “new” findings biases against verification
> Gold rush mentality (citations, funding, no replication)
Has the way we do science contributed to the confusion tDCS
- ) File drawer phenomenon: publish positive results but not to publish negative or non confirmatory results
- ) Forking path phenomenon: Lack of specific predictions in the absence of a good understanding of how tDCS works
3.) Increase in importance of science communication:
Expectation > Truth with single result. Single result can define field if widely promoted
