Methods of Localization, how to study the brain

Week 3 Sept. 19

Methods of localization

• Accident

• Manipulation

• Measurement

Neuropsychology

Branch of psychological science that examines how brain injury affects the mind

• Vascular injury (e.g. strokes)

• anoxia (loss of oxygen)

• disease

• penetrating wounds (e.g. gun shots)

• surgery

Brain damage

• In an injury to a specific brain regions reliably causes a specific dysfunction → this region is necessary for correct functioning

• Broca’s area and Wernicke’s area 

Wernicke’s Area 

• TEMPORAL 

  • speech comprehension

Broca’s area 

• FRONTAL LOBE 

  • Speech production

  • think hearing blah, blah, blah, saying words

Aphasia 

• Inability to comprehend or produce speech, or both 

Agnosia

• Inability to recognize objects, shapes, sounds, smells, and people 

Amnesia

• Inability to remember 

Five seconds of summer….I wish that I could wake up with amnesia and forget about the stupid little things

Brain mapping system

• Ex vivo; after death (post-mortem) 

• Ex vitro; slices, culturs (VITRO Latin for "in glass") 

• In vivo; with all the living, invasive and non-invasive 

• Vivo; living 

What type of activity is neural activity and how do we measure it?

• ELECTROCHEMICAL

  • Ways to measure 

• Electrical activity

• Chemical activity 

Methods for recording brain’s electrical/magnetic output

• The electroencephalogram (EEG)

• Even-related potentials (ERPs)

• Magnetoencephalography (MEG)

• Single-cell recordings  

What two methods measure brain activity?

• electroencephalogram (EEG)

• Magnetoencephalograph (MEG)

  • they record electrical and magnetic activity in the brain

  • they DO NOT visual brain activity

EEG Method

• Electrodes placed on the scalp

• Activities of cortex zones are recorded 

• Temporal resolution is very good 

• Spatial resolution is not so good 

• Reflects the sum of all postsynaptic potentials occurring in multiple neurons

  • used in sleep studies

• Event related potentials (ERPs)

  • Used in cognitive studies

Event-related potentials

• Analysis allows researchers to map the brain’s EEG response to environmental stimuli

• In this examples, a characteristic waveform emerges

  • when responses to the presentation of a tone are average over 100 trials

Magnetoencephalography (MEG)

• Electrical activity in the brain generates measurable magnetic fields

  • Electromagnetic fields generated by the brain

    • Cannot take activity from all over the brain

    • Difference from EEG; conductivity of the tissues inside the skull has little effect on the magnetic fields outside of the skull  

Difference between EEG and MEG?

The conductivity of the tissues inside the skull has little effect on the magnetic filed outside of the skull

Positron emission tomography (PET)

• High resolution of the brain is obtained 

• Radioactive chemicals (marker) injected into the blood 

• Relationship between the density signal of that marker and the blood flow in that area 

• Color of the image indicates the level of activity 

  • RED most active, followed by yellow, green, blue for least active 

• Involves taking dose of radiation

Functional magnetic resonance imagine (fMRI)

• Magnetic detectors amount of hemoglobin and oxygen in different areas of the brain 

• Highly active areas of the brain appear to use more oxygen 

• Indicate where blood flows in brain for specific cognitive processing, based on magnetism 

• Used to develop brain regions maps 

fMRI pros and cons

• Provides images of the structure and activity of the brain 

• High detail and safe 

• Time-consuming, expensive, patient must be lying still on the table 

• Studying the relative activity of brain tissues in real-time 

The brain and the self

• If you lose part of the brain, you lose part of your unique experience 

• Brain activity and mind are inseparable

  • on is the other