measuring brain activity

brain imaging

way to asses brain structure and function in a non-invasive way (contradiction with lobotomies and leucotomies)

electro-ence-phalography (eeg) - refers to both the equipment/method and data output

most diagnostic tests for epilepsy

history of eeg

1924: first human eeg 1934: first demonstration of epileptiform spikes w eeg

strengths of eeg

good temporal resolution, relatively cheap, portable, safe and well tolerated by patients

limitations

poor spatial resolution, only detects activity on surface of the cortex

electrophysiology - single neurons (come back to this one)

hodgkin and huxley 1952

Strengths of electrophysiology

records directly from individual neurons

limitations of electrophysiology

high risk of infection, only possible to record a few neurons at a time

magnetic resonance imaging

exploits magnetic properties of brain tissue. MRI coil generates a strong magnetic field. stronger than earth’s magnetic field

MRI - structural imaging

magnetic field passes through a person's head, causing hydrogen atoms to align with magnetic fields.

• radio frequency waves temporarily disrupt the alignment causing a signal that is detected

• because diff parts of brain contain diff amts of water, they emit diff signals

MRI - diffusion tensor imaging (DTI)

uses same MRI equipment as structural imaging to detect large axon tracts (white matter) that dlow through the brain and connect diff reigons of cortex

MRI - fMRI (come back to this)

cognitive processes use energy → production of energy uses oxygen from haemoglobin.

MRI strengths

high spatial resolution, identifies specific anatomical/structural and functional properties

MRI limitations

very expensive, safety risks, specialised staff

positron emissions tomography (PET)

radioactive substances known as tracers to visualise all glucose metabolisms or the neurotransmitter/receptor function

• can also use traceres to bind exclusively to proteins of interest → used as diagnostic tool for Alzheimers to detect buildup of amaloid protein

strengths of pet

can detect different chemicals in the brain

limitations of pet

expensive, relatively low spatial recognition, required radioactive tracers to be injected into blood

modifying brain function

using different methods

• brain reigons can be permenantly removed/destroyed so brain activity can be temporarily decreased

• brain areas can be stimulated to enhance or increase brain activity in that region

enhancement

imporvement of healthy btain function to above or better than normal

ablation studies

deliberate lesions allow a relatively high degree of precision. for research, animals are used. however, human ablation was used for medical treatment

surgical ablation

egas moniz - prefrontal leucotomy for relief of psychiatric disorders. considered successful at the time

frontal leucotomy processes

EITHER leucotome inserted into one of several holes drilled into skull. wire was extruded from the tip and leucotome rotated to remove core of tissue

OR cut above the eyelid, implement pushed through the base of skull and rocked side to side to slice through frontal lobes, seperating from rest of the brain

frontal leucotomy impacts

• severe personality changes, inability to plan, emotional unresponsiveness

• popularised → water freeman

• 40, 000 operations in us

electrical brain stimulation

used to reveal localisation of cortical function

1870 - frisch and hitzig electrically stimulated part of frotnal lobe cortex in dogs. induced contradictions of specific muscles on contralateral side of body

non incasive brain stimulation (ect)

electroconvulsive therapy (ect) invented in italy in 1930s

already known that seizures reduced psychiatric symptoms. early as 1500 inducing seizures were used to treat psychiatric conditions

ect attempted to stimulate that

tDCS

range of non-invasive methods for brain stimulation, most common is transcranial direct current stimulation

tms

transcranial magnetic stimylation

• coil carrying an electrical current generates brief, focal magnetic pulse. activates small region of cortex (~10-15 nm)

• acts as ‘virtual leison’ temporarily disrupts tissue. non painful unless it causes muscle contractions