H3 electrophysical brain

• Representations


  Properties of the world that are manifested in cognitive systems
• Mental representation


  The sense in which properties of the outside world (e.g. colors, objects) are copied/simulated by cognition
• Neural representation


  The way in which properties of the outside world manifest themselves in the neural signal (e.g. different spiking rates for different stimuli)
• Single-cell recordings


  1. Measure the responsiveness of a neuron to a given stimulus (in terms of action potentials per second)

  2. An electrode may pick up on activity from multiple nearby neurons and is referred to as a multi-cell (or multi-unit) recording

  3. Special algorithms can then be applied to separate the combined signal into individual contributions from different neurons
• Electroencephalography (EEG)


  • Measurements of electrical signals generated by the brain through electrodes placed on different points on the scalp (non-invasive)
  • Measure number of action potentials per second
  • Measure relative timing of cognitive events and neural activity
  • Continuous measure of brain activity over time
• Event-related potential (ERP)


  • The average amount of change in voltage at the scalp that is linked to the timing of particular cognitive events (e.g., stimulus, response)
  • EEG signal is averaged over many events to reduce effects or random neural firing
  • EEG is averaged and synchronized to some aspect of the event (eg pressing a button)
  • Links the amount of change in voltage at the scalp with particular cognitive events (e.g., stimulus, response)
  • Links the rate of change of the EEG signal to cognitive processes (oscillation-based measures)
• Reaction time


  The time taken between the onset of a stimulus/ event and the production of a behavioral response (e.g., a button press)
• Multi-cell recordings (or multi-unit recordings)


  The electrical activity (in terms of action potentials per second) of many individually recorded neurons recorded at one or more electrodes
• Grandmother cell


  A hypothetical neuron that just responds to one particular stimulus (e.g., the sight of one's grandmother)
• Types of neural representation

  • Local representation
  • Fully distributed representation
  • Sparse distributed representation
• Rate coding


  The intensity or strength of a stimulus is encoded by the firing rate of neurons, higher stimulus intensity leads to higher firing rates, and vice versa
• Temporal coding


  Synchrony of firing by a population of neurons to code the same stimulus or event
• Dipole


  A pair of positive and negative electrical charges separated by a small distance
• Mental chronometry


  The study of the timecourse of information processing in the human nervous system. It involves measuring the speed and accuracy of various mental tasks to understand the underlying cognitive mechanisms
• Sternberg's Additive factors method

  1. Encoding the probe digit

  2. Comparing the probe digit with the items held in memory

  3. Deciding which response to make

  4. Responding by executing the button press
• N170


  An ERP component (negative potential at 170 ms) linked to perceiving facial structure
• Associative priming


  Reaction times are faster to stimulus X after being presented to stimulus Y, if X and Y have previously been associated together and related
• ERP component categories


  • Exogenous (related to physical/sensory properties of the stimulus)
  • Endogenous (related to properties of the task)
• ERP spatial and temporal resolution

  • ERP has good temporal resolution but poor spatial resolution
  • The difficulty of locating the sources of electrical activity from measurements taken at the scalp (Inverse Problem)
  • Dipole modeling: Assuming how many dipoles (regions of electrical activity) contribute to the signal recorded at the scalp
• Magnetoencephalography (MEG)


  A noninvasive method for recording magnetic fields generated by the brain at the scalp, with much better spatial resolution than EEG