W11- Brain Stimulation & ECoG

What is Transcranial Magnetic Stimulation (TMS)?

A non-invasive brain stimulation technique that uses magnetic fields to induce electrical currents in the cortex.

How does TMS work?

A rapidly changing magnetic field induces electrical activity in neurons beneath the coil.

What is the main advantage of TMS?

It allows researchers to manipulate brain activity and make causal inferences about brain function.

What is single-pulse TMS?

A single magnetic pulse delivered to the cortex to examine neural excitability or timing of processing.

What is repetitive TMS (rTMS)?

A series of TMS pulses delivered repeatedly over time to alter cortical activity.

What is a Motor Evoked Potential (MEP)?

A muscle response produced following stimulation of the primary motor cortex.

How are MEPs measured?

Using electrodes placed on muscles to record activity following TMS stimulation.

What does a larger MEP indicate?

Greater excitability of the motor system and activation of more motor neurons.

What is an application of MEPs in research?

Measuring changes in motor cortex excitability during perception, action observation, or cognitive tasks.

What is a virtual lesion?

A temporary disruption of normal brain activity produced by TMS.

Why are virtual lesions useful?

They allow researchers to test whether a brain region is necessary for a cognitive function.

How does TMS create a virtual lesion?

By introducing neural noise that temporarily disrupts information processing.

What is online TMS?

TMS delivered while a participant is performing a task.

Why is online TMS useful?

It allows researchers to determine when a brain region contributes to processing.

What is offline TMS?

TMS delivered before a task begins.

Why is offline TMS useful?

It allows researchers to examine longer-lasting effects on cognition and behaviour.

What frequency of rTMS is generally considered inhibitory?

Low-frequency stimulation (approximately 1–5 Hz).

What frequency of rTMS is generally considered excitatory?

High-frequency stimulation (greater than 5 Hz).

Why should frequency effects be interpreted cautiously?

The relationship between stimulation frequency and excitatory/inhibitory effects is not always consistent.

Who was Wilder Penfield?

A neurosurgeon who mapped cortical functions through electrical stimulation during epilepsy surgery.

Why were Penfield's patients awake during surgery?

The brain lacks pain receptors, allowing patients to report their experiences during stimulation.

What was Penfield's goal during cortical stimulation?

To identify important functional areas before removing epileptic tissue.

What did stimulation of the visual cortex typically produce?

Flashes of light, colours, and visual sensations called phosphenes.

What are phosphenes?

Visual sensations produced by direct stimulation of the visual cortex in the absence of visual input.

What did stimulation of the auditory cortex produce?

Ringing, buzzing, clicking, and other simple auditory sensations.

What did stimulation of the somatosensory cortex produce?

Tingling, numbness, and sensations of movement.

What did stimulation of the motor cortex produce?

Involuntary movements of body parts controlled by the stimulated area.

Why is motor cortex stimulation important for understanding voluntary action?

Patients moved but often reported they had not intended to move.

What did Penfield's studies demonstrate about brain organisation?

Strong evidence for localisation of function.

What happened when Penfield stimulated language-related regions?

Speech production could be disrupted or temporarily halted.

What does speech disruption during stimulation suggest?

The stimulated region is necessary for normal language processing.

What is Electrocorticography (ECoG)?

A method that records electrical activity directly from the cortical surface using implanted electrodes.

How does ECoG differ from EEG?

ECoG records directly from the cortex beneath the skull, whereas EEG records from the scalp.

What is the main advantage of ECoG over EEG?

Much higher spatial resolution and reduced signal distortion.

What is the temporal resolution of ECoG?

Excellent temporal resolution on the millisecond scale.

What is a major limitation of ECoG?

It can only be used in patients undergoing neurosurgery.

Why is ECoG commonly used in epilepsy patients?

To identify the precise origin of seizures before surgery.

What is a Brain-Computer Interface (BCI)?

A system that translates brain activity into commands for an external device.

What is the main purpose of a BCI?

To bypass normal motor pathways and allow direct control of technology using brain activity.

Who benefits most from BCIs?

Individuals with paralysis, locked-in syndrome, or severe motor impairments.

What is the first step in a BCI system?

Recording brain activity using electrodes.

What is the second step in a BCI system?

Decoding the neural signals.

What is the third step in a BCI system?

Translating decoded signals into commands.

What is the final step in a BCI system?

Controlling an external device such as a cursor or robotic arm.

What types of devices can BCIs control?

Computers, wheelchairs, robotic limbs, communication systems, and prosthetics.

Why do BCIs require training?

The computer must learn the user's neural patterns and the user must learn to generate reliable signals.

What is a major limitation of BCIs?

Signal decoding can be difficult and accuracy may vary over time.

Why are implanted BCIs often more effective than non-invasive BCIs?

They provide stronger and more precise neural signals.

What is the major strength of brain stimulation methods such as TMS?

They provide causal evidence about brain function.

What is the major weakness of invasive brain stimulation methods?

They require surgery and are typically limited to clinical populations.