NEU 310 module 1

Historical Perspectives, Electrical imaging techniques, metabolic methods

Galen (~200 AD)

Believed the brain was the seat of consciousness, sensation, and cognitive actions.

Pierre Flourens (1815)

Performed lesions on animals, studied the vestibular system in pigeons; pioneer of brain function theory.

Paul Broca (1860s)

Localized speech production to "Broca's area" in the left frontal lobe.

Carl Wernicke (1870s)

Localized speech comprehension to "Wernicke's area" in the left temporoparietal region.

Karl Lashley (~1920s)

Proposed "mass action": the extent of brain damage disrupts function, not the specific location of damage.

Brenda Milner (~1950s)

Studied patients who had brain tissue removed to treat epilepsy; pioneered research on the temporal lobe's role in memory.

Wilder Penfield (~1950s)

Created the "homunculus," a map of body representation across the sensory/motor cortex.

Roger Sperry (~1960s)

Studied split-brain patients and hemisphere lateralization.

Phineas Gage

Suffered a frontal lobe injury (1848, tamping iron through skull) that caused major personality changes without loss of memory or other cognitive functions.

Lesion method

Using dysfunction (brain damage) to infer normal function; damage to a region causing loss of a function implies that region is responsible for it.

Orbitofrontal cortex

Region within the frontal lobe identified (via Phineas Gage) as responsible for affecting emotion.

Prefrontal cortex (damage effects)

Damage causes profound changes to personality without other apparent neurological deficits.

Double dissociation

When one lesion impairs cognitive function A but not B, and a different lesion impairs B but not A, showing the two functions are independent.

Split-brain patients

Patients whose corpus callosum has been surgically severed (often to treat epilepsy); used to study hemisphere lateralization.

Corpus callosum

Band of fibers connecting the two brain hemispheres; when severed, creates a "split brain."

Divided visual field technique

Presenting stimuli to the left or right visual field to determine which hemisphere processes it, based on contralateral visual processing.

Contralateral visual processing

Left visual field is processed by the right hemisphere; right visual field is processed by the left hemisphere.

Dichotic presentation

Playing different sounds to each ear at the same time to study hemispheric specialization for auditory/verbal processing (only right-ear sounds can be verbalized).

Wada test

Injecting a barbiturate (e.g., amytal) into the carotid artery to temporarily inhibit one hemisphere and test lateralization of function.

Left hemisphere specialization

Language and verbal communication; more analytical and feature-focused processing.

Right hemisphere specialization

Spatial and emotional information; non-verbal communication; gestalt/holistic processing; also localizes face processing.

Pros of the lesion method

Effectively demonstrates cause and effect; provides evidence of double dissociation and functional lateralization.

Cons of the lesion method

Lesions vary from person to person (single-case vs. group studies); shows a region is necessary but not that it's sufficient; doesn't address anatomical reorganization or compensatory strategies.

X-ray imaging

What it does: uses external radiation, exploiting different tissue penetration levels, to create an image. Used for: distinguishing hard tissue (bone/skull) from soft tissue; historically complemented the lesion method.

Single cell recording

What it does: directly records electrical activity from one (or a few) neurons via intracellular/extracellular electrodes; can capture local field potentials. Used for: highly precise studies of individual neuron responses (e.g., how photoreceptors respond to light); invasive, limited to few cells.

Microelectrode array

What it does: bundles many tiny electrodes together to record from an entire patch of tissue at once. Used for: recording population-level cellular activity while keeping single-cell precision.

Electrocorticography (ECoG)

What it does: places electrodes below the skull and above the cortex, capturing local field potentials from groups of neurons (not single cells). Used for: intermediate-resolution recording, often in clinical/surgical contexts like epilepsy monitoring.

Electroencephalography (EEG)

What it does: scalp electrodes record summed electrical activity from populations of neurons in a scalp topography (e.g., electrode F3 = frontal region 3). Used for: non-invasive, cost-effective studies of brain states (sleep, attention) and frequency-based analyses.

EEG frequency bands

Delta (0.5-4Hz) = deep sleep; Theta (4-8Hz) = memory/light sleep; Alpha (8-13Hz) = relaxed; Beta (13-30Hz) = alert/attentive; Gamma (30-100Hz) = heightened awareness.

Phase coupling (EEG)

What it is: synchrony between the phases (upstates/downstates) of two different-frequency waveforms (e.g., theta and gamma). Used for: showing brain regions/oscillations are working together, such as memory consolidation during sleep.

Event-Related Potentials (ERP)

What it does: averages continuous EEG signal across many trials to extract the electrical response to one specific stimulus/event. Used for: isolating a brain response to a particular event out of noisy background EEG.

N400

What it is: a negative ERP waveform peaking ~400ms after a stimulus. Used for: detecting responses to semantically unexpected or surprising stimuli (e.g., an odd word in a sentence).

P300

What it is: a positive ERP waveform peaking ~300ms after a stimulus, elicited by rare "oddball" stimuli. Used for: deception detection (lie detection) and studying attention/task relevance.

Magnetoencephalography (MEG)

What it does: measures magnetic fields produced by cortical depolarization using a SQUID sensor in a magnetically shielded room; fields aren't dampened by the skull. Used for: studies needing better spatial resolution than EEG while keeping excellent temporal resolution; expensive and uncommon.

Pros/cons of cellular recording (single cell/ECoG)

Pros: directly observes brain function, excellent temporal resolution, good (but limited) spatial resolution. Cons: invasive, difficult to study complex tasks.

Pros/cons of EEG

Pros: excellent temporal resolution, relatively cost-effective, non-invasive. Cons: bad spatial resolution, ERPs require many trials, movement/eye blinks disrupt the signal.

Pros/cons of MEG

Pros: similar temporal resolution to EEG, better spatial resolution than EEG. Cons: way more expensive than EEG, requires specialized setup, not very common.

Magnetic Resonance Imaging (MRI)

What it does: a powerful magnet aligns protons in water molecules; a radio frequency pulse disrupts alignment, and released energy as protons realign is detected to form cross-sectional images. Used for: high-resolution 3D structural imaging - identifying anatomy/damage and comparing volume, shape, cortical thickness. No task needed; doesn't measure activity.

Diffusion Tensor Imaging (DTI)

What it does: uses an MRI machine to measure the direction water molecules diffuse, mapping white matter tracts. Used for: measuring connectivity changes across the lifespan, establishing connections between brain regions, and testing myelination disorders (e.g., multiple sclerosis).

Magnetic Resonance Spectroscopy (MRS)

What it does: uses an MRI machine to measure the concentration of substances (e.g., neurotransmitters) in a target area, since each substance's chemical makeup causes protons to align differently. Used for: measuring brain metabolism/chemical concentration of specific, high-concentration substances (e.g., glutamate).

Positron Emission Tomography (PET)

What it does: a radioactive tracer is injected into the bloodstream; regions with higher metabolic activity take up more tracer and emit more positrons/photons, detected by a circular array. Used for: measuring brain metabolism and specific molecules, typically in clinical contexts.

SPECT

What it is: a scaled-down version of PET with fewer sensors. Used for: similar applications to PET at lower cost/resolution.

Functional MRI (fMRI)

What it does: measures the BOLD (Blood Oxygen Level Dependent) signal - the difference between oxygenated and deoxygenated hemoglobin - based on the assumption that active neurons need more oxygen. Used for: locating brain activity with excellent spatial resolution; BOLD signal peaks ~7s after a stimulus, with brain scans every ~2s (poor temporal resolution).

fMRI: task-based approach

What it does: compares the BOLD signal between two or more conditions/tasks (location and pattern of activation, e.g., MVPA). Used for: determining which brain area is more active for one cognitive task versus another.

fMRI: resting-state approach

What it does: scans participants with no task and measures co-variation (correlation) of activity across brain regions as the mind wanders. Used for: identifying resting-state networks, such as the default mode network.

Functional Near-Infrared Spectroscopy (fNIRS)

What it does: a near-infrared laser and optic fiber detectors measure light absorption (slow signal, like BOLD) and light scattering (fast signal, called EROS, like ERPs). Used for: studies where participants must move (e.g., infant research); records only surface-level cortical activity.

Transcranial Magnetic Stimulation (TMS)

What it does: a pulsed magnetic field over the scalp temporarily excites or inhibits brain activity (like a temporary, reversible lesion). Used for: establishing cause-and-effect relationships between a brain region and a function; growing clinical use (e.g., depression treatment).

Transcranial Direct Current Stimulation (tDCS)

What it does: a weak direct electrical current runs through the scalp/skull/brain between entrance and exit electrodes, exciting or inhibiting activity without precise spatial focus. Used for: promising clinical applications such as stroke recovery, and improving attention or memory; cheap and generally safe.

tACS

What it is: a variant of tDCS that uses alternating current instead of direct current.

Pros/cons of MRI & DTI

Pros: non-invasive (though uncomfortable), excellent spatial resolution. Cons: expensive, no temporal resolution, does not show brain activity.

Pros/cons of MRS

Pros: non-invasive, measures brain metabolism. Cons: relatively poor spatial and temporal resolution; only works for a limited set of high-concentration substances.

Pros/cons of PET

Pros: measures brain activity/metabolism and specific molecules. Cons: takes a long time (minutes) due to radioactive half-life, exposes patients to radiation, mostly used in clinical contexts.

Pros/cons of fMRI

Pros: non-invasive, measures brain activity, excellent spatial resolution. Cons: indirect measure (blood, not neurons), can't be used with metal implants, poor temporal resolution (~2s), requires extensive data processing.

Pros/cons of fNIRS

Pros: non-invasive, good temporal resolution (EROS), participants don't need to stay completely still (useful for infants). Cons: only records surface-level brain activity.

Pros/cons of TMS

Pros: non-invasive, shows cause-and-effect to an extent, growing clinical applications (e.g., depression). Cons: can cause headaches, muscle twitches, nausea, or (rarely) seizures.

Pros/cons of tDCS

Pros: very cheap, few side effects, generally safe, promising clinical applications. Cons: very poor spatial resolution, not very common yet, cheapness has led to risky "DIY" cognitive-enhancement attempts.