W1L2 - Electrical signals in the brain

Question 1

What are the methods for Intracranial electrical recordings

Answer 1

Single cell animal studies

ECoG

Question 2

What are the methods for Extracranial electrical recordings

Answer 2

EEG

ERP

Question 3

What are the methods for Intracranial electrical stimulations

Answer 3

DCES

Question 4

What are the methods for Extracranial electrical stimulations

Answer 4

tDCS

Question 5

What is the history of intracellular and extracellular recordings

Answer 5

Intra: Recording of giant axon in squid
Extra: Single neurons in visual cortex of anasthetized cats

Question 6

Extracellular Recordings of Single Neurons: Types

Answer 6

Anaethsized Studies: Sensory and Motor
Awake behaviour Studies: Higher level functions like attention

Mulitple neurons can be studied with electrode arrays

Question 7

What is Local Field Potential. What is the pros and caveat.

Answer 7

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)

Question 8

ECoG overview. What is it used to clinically

Answer 8

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

Question 9

ECoG pros

Answer 9

1.) High spatial and temporal resolution
2.) Both single/multi-unit recording
3,) Understanding how indirect methods like fMRI relate to direct neural responses

Question 10

ECoG + BOLD Study. Results.

Answer 10

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

Question 11

EEG Overview

Answer 11

Electrical activity measured depends on large no. of synchronous, aligned neurons

Usually recording pyramial neurons (best for cortical gyri not sulci)

Question 12

EEG Pros

Answer 12

1. ) Cheap

2. ) Good Temporal

Question 13

EEG Cons

Answer 13

1. ) Not good for deep structures

2. ) Poor spatial

Question 14

How does EEG move to ERP

Answer 14

x1000 trials + signal averaging

Question 15

DCES Overview

Answer 15

Stimulation of Single Neurons, mostly on awake behaving non-human primates
Same electrodes as ECoG

Question 16

DCES Cons

Answer 16

Clinical patients limit the basic research

• Must have epilepsy
• No choice in electrode location (Gyrii + Seizure place)
• Surgery = Expensive

Question 17

tDCS Overview and Aim

Answer 17

• Passing a weak DC current between electrodes placed on the scalp
• The aim is to stimulate the brain and improve mental function

Question 18

tDCS vs other techniques

Answer 18

1. ) Does not require medical intervention
2. ) Uses DC to influence brain activity
3. ) Uses weak current to influence brain activity

Question 19

How does tDCS work

Answer 19

• 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

Question 20

tDCS problems

Answer 20

1. ) Precise mechanisms elusive

2. ) Precise and selective stimulation of a target brain region difficult

Question 21

tDCS pros

Answer 21

1. ) Non invasive
2. ) Cheap to purchase and use
3. ) Easy to use
4. ) Safe when using established protocols (straight forward ethics)

Question 22

Does scientific evidence suggest tDCS is effective

Answer 22

No. Meta-analysis found no reliable effect.

Criticism of meta-analysis: Not enough studies and poor designs.

Question 23

What are the difficulties in establishing whether tDCS is effective?

Answer 23

1. ) High prevalence of “adverse” events = strong placebo

2. ) No active sham control

Question 24

Has the rapid increase in studies contributed to the tDCS confusion?

Answer 24

High rates of “new” findings biases against verification

> Gold rush mentality (citations, funding, no replication)

Question 25

Has the way we do science contributed to the confusion tDCS

Answer 25

1. ) File drawer phenomenon: publish positive results but not to publish negative or non confirmatory results
2. ) 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