March 7, 2018
Transcranial Magnetic Stimulation (TMS) and EEGs and event-related potentials (ERPs)
≈ Microscopic anatomy: Brodmann areas
– brain segmented according to appearance in microscope (cytoarchitectonics)
– combined with comparative neuroanatomy
– appearance reflects type of cells (e.g. inputs vs outputs)
– type of cell sometimes correlates with function
– studies restricted to small number of brains
≈ Transcranial magnetic stimulation (TMS)
– stimulator, placed above scalp, contains a coil of wire
– brief pulse of high electrical current fed through the coil
– result: magnetic field: with flux lines perpendicular to the plane of the coil
– magnetic field induces electric field perpendicular to magnetic field
– electric field leads to neuronal excitation within the brain (trans-cranial)
– useful to study (1) behaviour during "virtual brain lesions", (2) chronometry, (3)
functional connectivity
– TMS effects depend on stimulation site
– Measuring TMS:
Motor cortex stimulation:
activates corticospinal neurons trans-synaptically
example: TMS coil 5 cm lateral from vertex >
often contralat' thumb twitches (20 ms post TMS)
record motor EPs (surface EMG, target muscle relaxed)
record silent period in contracted target muscles
~150 ms after motor cortex stim', cortical mechanisms
Occipital cortex stimulation:
excitatory effects: e.g. phosphenes;
inhibitory effects: suppression of motion perception and letter
identification
Somatosensory cortex stimulation:
may elicit tingling, block the detection of peripheral stimuli (tactile, pain)
can modify somatosensory evoked potentials (SEPs)
Auditory cortex stimulation: Interpretation of results challenging: loud coil
click
Frontal cortex stimulation: Effects on subject's mood? Potential for
therapeutic use?
Effects measured as peripheral responses, as impaired or altered perception,
as improved or impaired task performance, or as brain's direct response
(detected in EEG, PET, fMRI)
– TMS example application: study crossmodal plasticity in the brain
Blind people can learn to read Braille
Superior tactile perception (compared with sighted people)
Underlying changes in the brain? Blind persons’ visual cortex is known to be
activated during Braille reading
Functional significance of this activation? = research question for TMS studies
Transcranial Magnetic Stimulation (TMS) and EEGs and event-related potentials (ERPs)
≈ Microscopic anatomy: Brodmann areas
– brain segmented according to appearance in microscope (cytoarchitectonics)
– combined with comparative neuroanatomy
– appearance reflects type of cells (e.g. inputs vs outputs)
– type of cell sometimes correlates with function
– studies restricted to small number of brains
≈ Transcranial magnetic stimulation (TMS)
– stimulator, placed above scalp, contains a coil of wire
– brief pulse of high electrical current fed through the coil
– result: magnetic field: with flux lines perpendicular to the plane of the coil
– magnetic field induces electric field perpendicular to magnetic field
– electric field leads to neuronal excitation within the brain (trans-cranial)
– useful to study (1) behaviour during "virtual brain lesions", (2) chronometry, (3)
functional connectivity
– TMS effects depend on stimulation site
– Measuring TMS:
Motor cortex stimulation:
activates corticospinal neurons trans-synaptically
example: TMS coil 5 cm lateral from vertex >
often contralat' thumb twitches (20 ms post TMS)
record motor EPs (surface EMG, target muscle relaxed)
record silent period in contracted target muscles
~150 ms after motor cortex stim', cortical mechanisms
Occipital cortex stimulation:
excitatory effects: e.g. phosphenes;
inhibitory effects: suppression of motion perception and letter
identification
Somatosensory cortex stimulation:
may elicit tingling, block the detection of peripheral stimuli (tactile, pain)
can modify somatosensory evoked potentials (SEPs)
Auditory cortex stimulation: Interpretation of results challenging: loud coil
click
Frontal cortex stimulation: Effects on subject's mood? Potential for
therapeutic use?
Effects measured as peripheral responses, as impaired or altered perception,
as improved or impaired task performance, or as brain's direct response
(detected in EEG, PET, fMRI)
– TMS example application: study crossmodal plasticity in the brain
Blind people can learn to read Braille
Superior tactile perception (compared with sighted people)
Underlying changes in the brain? Blind persons’ visual cortex is known to be
activated during Braille reading
Functional significance of this activation? = research question for TMS studies
