The Speed of Thought

Question 1

Helmholtz and the speed of thought

Answer 1

• by mid 19thC, elements were in place for neuroscientific study of perception
• Helmholtz set out to demonstrate that nerves conduct signals at finite velocity
• 10s of m/s (slow)

Question 1

Pathways in visual perception

Answer 1

• Retina: photoreceptors, bipolar cells, ganglion cells
• Thalamus (LGN)
• Primary visual cortex
• ‘Higher’ visual cortices

Question 2

State the different recording electrical activity of the nervous system: from lowest to highest resolution

Answer 2

-EEG
-ECoG
-Extracellular recording
-Intracellular recording

Question 3

EEG (electroencephalography)

Answer 3

• ordered structure of cortex means summed activity of many neurons generates currents that can sum to generate small voltage changes (field potentials)
  
  • which can be amplified and recorded from the surface of the head

Question 4

ECoG

Answer 4

• similar to EEG, but electrodes placed directly on cortical surface (e.g., prior to neurosurgery).
• Record local field potentials due to summed neural activity, cannot resolve individual neural activity.

Question 5

Extracellular recording

Answer 5

• micro electrodes inserted into extracellular space
• APs in nearby neurons generate small extracellular currents that can be amplified and picked up as ‘spikes’.

Question 6

Intracellular recording (highest resolution)

Answer 6

micro electrodes inserted through cell membrane records voltage difference between intra- and extracellular space.

Question 7

Signal averaging: Event related potentials (ERP)

Answer 7

• using EEG to study responses to sensory stimulation
• since signal from a single electrode is due to activity of thousands to millions of neurons, any response is lost in the noise due to activity of many neurons unrelated to the stimulus
• however, if stimulus is repeated many times and averaged, random activity tends to cancel out, revealing a signal related to the stimulus