L2 - the lesioned brain, introduction to none-invasive brain stimulation

Question 1

TMS

Answer 1

• transcranial magnetic stimulation

- a means of disrupting normal brain activity by introduction noise (virtual lesions)

Question 2

Faraday’s coil

Answer 2

Michael Faraday first discovered the electromagnetic induction principle

Question 3

how does TMS work:

Answer 3

TMS causes neurons underneath the stimulation site to be activated - if they are involved in performing a critical cognitive function then stimulating them artificially will disrupt that function

Question 4

advantages of TMS:

Answer 4

• interference/virtual lesion technique
• transient and reversible
• control location of stimulation
• establishes a causal link of different brain areas and a behavioural task

Question 5

Transcranial electric stimulation - tES

Answer 5

tES uses low level (1-2 mA) currents applied between two stimulating pads.

current can either flow:

1. in one direction = transcranial direct current stimulation (tDCS) - most common
2. rhythmically alternate in direction = transcranial alternating current stimulation (tACS)
3. or current can randomly change direction = transcranial random noise stimulation (tRNS)

Question 6

tES protocols:

Answer 6

• in direct current stimulation, current flows anode (pos) to cathode (neg)
• in alternating current stimulation, current flows other way at frequency that is pre-set.

anodal tDCS = increases cortical excitability and performance

cathodal tDCS = decreases cortical excitability and performance.

Question 7

neurotransmitters and tDCS:

Answer 7

• anodal stimulation inhibits GABA (inhibitory neuron)

- cathodal stimulation inhibits glutamate (excitatory neuron)

Question 8

Transcranial alternating current stimulation (tACS)

Answer 8

• the synchronisation of internal brain rhythms with externally applied oscillating electric fields .
• these fields cause PHASE-LOCKING of a large pool of neurones = increases of neural synchronisation at the corresponding frequency

Question 9

Voss et al 2014

Answer 9

• inducing and lucid dreaming

EEG was measured for 27 Ps not in lucid dreams and tACS was applied for 2 mins

• 2 mins after Ps in REM phase - tACS applied for 30sec in range of 20-100Hz - Ps then woken up to report dreams on luCID scale
• findings: EEG showed brains GAMMA activity increased during stimulation with 40Hz - less so with 25 Hz

Question 10

important conclusions of Voss et al 2014

Answer 10

• non-invasive brain stimulation has prominent effect on cognitive processes
• TMS and tES can cause after effects on excitability of neurons and networks
• offer promising alternatives to pharmacological interventions and can enhance cognitive performance

Question 11

two traditions of neuropsychology:

Answer 11

1. classical neuropsychology (what functions are disrupted by damage to region x?)
   - looks at functional specialisation
   - uses group study methods
2. cognitive neuropsychology (can a particular function be spared/impaired relative to other cognitive functions)
   - use single case
   - addresses questions of the building blocks of cognition

Question 12

causes of brain damage:

Answer 12

• cerebrovascular accident
• neurosurgery
• viral infections
• tumour
• head injury
• neurodegenrative

Question 13

types of stroke

Answer 13

• ischaemia (lack of glucose and oxygen supply)

- haemorrhage is bleeding into the brain tissue - vessel bursts and blood flow into brain region - drowning of neurons

Question 14

single dissocations:

Answer 14

single dissociation: patient is impaired on a particular task (TASK A) but relatively spared on another task (TASK B)

• if patient performs within normal range on task B - this is classical single dissociation
• if patient impaired on both, but significantly more on one of the tasks - this is STRONG single dissocaiton

Question 15

Patient CF

Answer 15

• suffered ischaemic stroke to left parietal area (angular gyrus)
• could only write with his left hand
• when writing words he systematically omitted vowel only

Question 16

double dissociations

Answer 16

• derived from 2 or more single cases with complementary profiles
• brain has separate neural resources for processing written vowels relative to consonants e.g.

Question 17

examples of double dissociation:

Answer 17

Broca’s aphasia VERSUS Wernicke’s aphasia

• Brocas - problems with language production
  Wernicke’s - problems with difficulty in meaning of language but have relatively fluent speech

Question 18

single case studies

Answer 18

in cognitive neuropsych - data from different patients are not combined.

issues?
- lesions need to be assessed for each patient and NO GUARANTEE the same anatomical lesion

Question 19

group studies:

Answer 19

1. grouped by syndrome (DV - lesion location)
2. grouped by symptoms (DV - lesion location)
3. grouped by lesion location