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Lecture

NATS 1860 Note 16.docx


Department
Natural Science
Course Code
NATS 1860
Professor
Keith Schneider

Page:
of 7
NATS 1860 Note 16
Grading
- 15% Final Exam
o 10-15 essay questions will be distributed two weeks before the exam
(April 4)
It will consists of four questions randomly chose from those
provided
These will be written without notes or resources
- 5% each for two labs
o There will be two/three labs
o One lab: neuroimaging (1:30 or 2:30p.m., March 7, 14,21,28)
o Two lab: consciousness (1:30p.m., March 7,14)
o Three lab: memory/cognition/language (1:30 p.m., March 21,28)
o You have to sign up on Moodle in advance,
Review of Brain
- It weighs about 3lbs
- ~ 100 billion neurons
- 1000-10000 synapses each
- ~ 100 trillion synapses
- ~100 trillion glial cells
- The brain is a competitional denies
- Humans have roughly 100 Terabytes of memory power in terms of
computational power v. memory capacity.
- Moore’s law:
o Gordon Moore described that every two years the number of
capacitors on a microchip is doubling
o Every two years our computer is becoming twice as more powerful
o Made in 1970 it’s a logarithmic scale
o By the year 2020 a computer will have the power of a human brain,
and in 2040 a computer will have the power of all human brains
combined
- Cerebral Cortex: this is the memory/pattern recognition,
compression/decompression
o It’s 1-4.5mm thick
o Surface area of ~2,500 cm^2
Equivalent to circle with diameter or 22in
Therefore, it fits when crumpled into the skull
o There is the thalamus in the center of the brain this station gates the
flow of information back and forth with the brain.
Brain Imaging
- The different method of imaging brain is how fast in time it can sample
information at the brain
o Can it look at neurons firing or temporal lesions?
This is the time resolution
- Spatial resolution: how small can you record someone’s space?
o Will you stick a small wire, or look at a large structure within the
brain
- The third is invasive or non-invasive where you need to cause a lesion.
- MEG and ERP can measure brain activity every millisecond
o It doesn’t have much spatial resolution, so it can’t see more than a cm
in size.
- There is a tradeoff occurs with you whether having spatial resolution and
how often you see something
- Spatial resolution refers to how small you can see someone’s brain:
o How big an object has to be before you can properly focus on it.
Electroencephalography
- The neurons in our brain are firing action potential and moving ions in the
brain and involves electrochemical activity
o There are disturbances in the electrical field
- A very small but detectable electric field can be measured on the surface of
the scalp using sensitive electrodes and amplifiers
- Electrodes are stuck to people’s heads with conductive gel being stuck
o These measure the electric field on our head
o The data comes out as a noisy data because there are lots of signals,
and you have to pull and organize specifically which signals you want
Different electrodes provide you with different frequencies
such as different oscillations
- Oscillation: if you measure a wave form (guitar string) it moves back and
forward
o Electrical waveforms do the same: the electrical field increases and
decreases amplitude over time
o When you pay attention to specific frequencies such as attention
signals it is the way that the brain communicates with itself
It is organizationally coming from cortex, thalamus, etc.
Information of ions going back and forth cause electric field
oscillations.
- Event-Related Potential
o As a convention the negative (upward) and positive (downward)
peaks are numbered. They are believed to reflect large population
activities in the brain.
o You might have an experiment that you do 100 times, average the
data, and create a stereotypical response to a single event in the EEG
- EEG:
o Advantages:
It has very good temporal resolution
o Disadvantages:
It has limited spatial resolution: it is difficult to accurately
localize the source of the measured signal
Confined to signals at surface of brain
It’s long and uncomfortable for test subjects
- MEG
o Similar to EEG, but involves magnetic field
o There is a big machine that you sit in, essentially it measures the
activity in the same way but have advantages
o Advantages:
Very good temporal resolution
Improved setup time and subject comfort compared to EEG
Less degradation of signal due to scalp, skull, etc. than EEG\
o Disadvantages:
Limited spatial resolution: it is difficult to accurately localize
It is also limited to the layer
It’s more expensive than EEG
Optical Imaging
- Looking directly on the surface of the cortex using a video camera
- You can either measure Intrinsic activity (blood flow), or you can measure
the electrical activity using voltage-sensitive dye
- Intrinsic focuses on the amount of blood flow you need to function a certain
form
- The voltage sensitive dye allows you to see the direct action potentials in a
given area
o You’re still looking at the surface of the brain.
- It requires you to cut open the subject’s head
- Mice use their whiskers as the most sensitive organ
o Each whisker has the barrel cortex to represent itself.
- Advantages:
o Has very precise temporal and spatial resolution
o Allows measurement and comparison of both intrinsic and electrical
activity
o It allows precision in
- Disadvantages:
o It’s very invasive: requires viewing access to the surface of the brain
o Confined to the surface of the brain
o For mice, this isn’t a problem because their cortex is smooth, but for
primates this is difficult because the cortex is hidden
Structural MRI
- This scanner uses strong magnetic fields and radio waves to form static
images of the brain
o These waves are then re-omitted
- It’s good for soft-tissue damage
- You can look at the gross anatomy, cortical thickness, and VBM (take a
population of people’s brain and morph them all together and see where you
have certain expansions then others.