Neurostimulation Flashcards
contraction: overview
- myosin can’t bond w actin (due to troponin-tropomyosin complex)
- Ca binds to complex to expose actin
- once bonded w actin, myosin heads pull actin filament toward centre of sarcomere
define: neuromuscular junction
- synapse formed btw å motor neuron axon + mm fibre
neuromuscular junction: define motor unit
- axon forming synapses w several mm fibres
neuromuscular junction: how to get precision of mm control?
- based on motor unit size:
- sml: precise movements of hand (fingers 1:<10)
- lrg: leg movements (1:>300)
neuromuscular junction: which NT used
- Ach
neuromuscular junction: release of Ach prod?
- prod large endplate potential
- voltage changes opens Ca channels
neuromuscular junction: Ca entry
- triggers myosin-actin interaction (rowing action)
- movement of myosin bridges shortens mm fibre
tension + tetany: aka
- wave summation + tetany AKA freq summation
tension + tetany: list types (4)
- twitch
- wave summation
- incomplete tetanus (unfused)
- complete tetanus (fused)
tension + tetany: how does wave summation occur?
- when set of cells repeatedly stimulated without relaxation
tension + tetany: define tetany
- sustained contraction resulting from high freq stimulation
tension + tetany: eg. external source
- peripheral electrical stimulation
reflex: H reflex
stimulus - dorsal root - SC - mm
- after stimulus + M-wave
name types of brain stimulation (5)
- transcranial magnetic stimulation (TMS)
- transcranial electrical stimulation (TES)
- deep brain stimulation (DBS)
- electroconvulsive therapy (ECT)
- direct cortical electrical stimulation (DCES)
DBS: involved
- implantation of electrode coils w wires going deep into brain
- for parkinsons disease
TES: list (4) types
- transcranial direct current stimulation (tDCS)
- transcranial alternating current stimulation (tACS)
- transcranial random noise stimulation (tRNS)
- sham stimulation
tDCS: list (2) types
- anodal
- cathodal
tDCS: features
- Aldini showed direct current stimulation improved mood of melancholy patients
- Albert found +ve and -ve stimulation had diff effects on cortical excitability
- recent interest in tDCS is renewed
tDCS: mechanism
- small electric current (~1 mAmp) passed through brain
- electrodes on scalp
- 9 volt current source
tDCS: which electrode is +vely/-vely charged?
+ve: anodal
-ve: cathodal
tDCS: way current flows from electrodes?
- from anode through skull + brain to cathode
tDCS: device features
- delivers current
- controls w set current intensity and duration of stimulation
tDCS: general features (3)
- noninvasive brain stimulation
- electrical currents delivered to scalp
- equivalent to voltages naturally prod by brain (1-2mA)
tDCS: anode electrode (4)
- +vely charged current
- stimulates nearby cortical regions
- increases +ve charge
- neurons more likely to reach AP
tDCS: cathode electrode (4)
- attracts -vely charged current
- inhibits nearby cortical regions
- increases -ve charge
- neurons less likely reach AP
tDCS: critical issues (3)
- tDCS is bipolar
- pure anodal/cathodal stimulation impossible
- NOT focal, no way to know where stimulation is occurring (be skeptical of current models)
tDCS: diy and foc.us gaming devices
- can diy ur own
- gaming devices to ‘enhance cognitive function’
- 2% cost of research/clinical grade sys
tDCS: experimental- 3 ver
- anodal
- cathodal
- sham
tDCS: experimental- sham?
- used as control in experiments
- emits brief current, remains off for remainder of time
- patient doesn’t know they aren’t receiving prolonged stimulation
tDCS: pros (6)
- cortical changes even after stimulation is ended (depends on length/intensity of stimulation)
- cheap
- portable
- relatively easy to use
- safe*
- bidirectional
tDCS: cons (3)
- poorly localised
- no temporal resolution
- can’t elicit AP
tDCS: experimental- Walsh
- ‘bullshit’ no evidence of cognitive effects after single session
- doubts of use
TMS: shape of wand
- using regular circle has large SA
- but 2 coils concentrate to smaller SA
TMS: pros- chronometry (2)
- timing the cont of focal brain activity to behaviour
- role of ‘visual’ cortex in tactile information processing in early blind subjects
TMS: virtual lesions- causal link btw
- brain activity and behaviour
TMS: real lesion eg.
- blind woman lost ability to read braille following bilateral occipital lesions
TMS: TMS lesion
- using sighted (blue) and E blind (red)
TMS: occipital TMS on braille reading result
- disrupts braille reading in early blind
- not control subjects
TMS: critical issues (3)
- online vs. offline design?
- online: how are sitmuli ordered?
- offline: how long experiment, r conditions dist evenly within lesion window?
coil localisation: find functional effect
- M1 (hand twitch- MEP)
- V5 (moving phosphenes)
coil localisation: find anatomical landmark
- inion/nasion - ear/ear vertex
- EEG 10/20 sys
coil localisation: move set dist along + across eg.
FEF = 2-4cm ant, 2-4cm lateral to hand area
coil localisation: but?
- not all brains are same
- MRI co-registration
- functional and structural scan
- frameless stereotactic sys
coil localisation: control conditions (5)
- diff hemisphere
- diff site (these have diff effect/ no effect)
- real
- sham (improper technique, extra padding)
or interleave TMS w no TMS trials
coil localisation: critical issues control conditions (5)
- control nonspecific stimulation effects
- control placebo/behavioural arousal etc.
- control sound
- control for extra physiological effects (eg. twitching)
- control for task specificity
coil localisation: major pros summary (6)
- reversible lesions without plasticity changes
- repeatable
- high spatial/temporal resolution
- can establish causal link btw brain activation and behaviour
- can measure/modulate cortical plasticity
- therapeutic benefits
coil localisation: major limitations summary (6)
- only regions on cortical surfaces can be stimulated
- can be unpleasant for subjects
- risks to subjects + esp patients
- stringent ethics required (can’t be used by some institutions)
- localisation uncertainty
- stimulation lvl uncertainty
safety: seizure induction-
- caused by spread of excitation
- single-pulse TMS has prod seizures in patients, not normal subjects
- rTMS: both
- visual and/or EMG monitoring for after discharges + spreading excitation may reduce risk
safety: hearing loss
- TMS loud click (90-130dB) in most sensitive range (2-7kHz)
- rTMS= more sustained noise
- reduced alot by ear plugs
safety: heating of brain
- theoretical power dissaption from TMS is few mW at 1Hz,
- brain metabolic power is 13W
safety: engineering safety
- TMS equipment operates at lethal voltages of up to 4kV
- max energy in capacitor is 500J = dropping 100kg from 50cm on your feet
safety: scalp burns form EEG electrodes
- mild scalp burns in subjects w scalp electrodes
- easily avoided eg. sml low-conductivity Ag/AgCl-pellet electrodes
safety: effect on cognition
- slight trend toward better verbal memory, improved delayed recall and better motor reaction time
safety: local neck pain and headaches
- related to stimulation of local mm and nn, site and intensity dependant
- particularly uncomfy over fronto-temporal regions
safety: effect on mood in normals
- subtle changes in mood are site, freq dependant
- high freq rTMS of L frontal cortex worsens mood
- high freq rTMS of R frontal cortex may improve mood
safety: contraindications
- metallic hardware near coil (pacemakers, medical pumps etc.)
- history seizures, history epilepsy in 1st degree relative
- medicines reducing seizure threshold
- pregnant
- history of serious head trauma
- history of substance abuse
- stroke
- status after brain surgery
- other medical/neurologic conditions assoc epilepsy/seizure will be hazardous
safety: critical issues (6)
- purpose of stimulation?
- type of stimulation?
- where is stimulation?
- stimulation adequate?
- control conditions?
- safety?
