Summary: Toolbox Neuroscientific Measures

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• Briefly describe neurotransmission.

  • Neurons communicate with each other by synaptic transmission.
    
  • a neurotransmitter is released in the synaptic cleft.
  • this neurotransmitter binds to a neurorecepeter, which is a gated ion channel.
  • the neuroreceptor opens, ions flow into the cell causing an ipsp or epsp.
  • depending on the current flow the extracellular fluid becomes more or less positive.

• What are the differences between action potentials and post synaptic potentials?

  Action potential vs postsynaptic potential;
  

  • take place at the axon - take place at the synaptic cleft/dendretic spine
  • neural output - neural input
  • arise when psp's summate across threshold - arise from presynaptic ap
  • constant in characteristics - can vary in size, duration, etc.
  • lasts several milliseconds - lasts several hundreds of milliseconds

• How does a neuron in the cortex form a dipole?

  • If a neuron receives an epsp in the dendrite, positively charged sodium ions will flow into the cell.
    
  • This causes the extracellular fluid of the location where the epsp was received to be negatively charged.
  • in the meanwhile, the extracellular fluid around the cell body is still positively charged.
  • this causes the neuron to function like a dipole; a pair of charges with opposite polarity, separated by a small distance

  the story is the other way around for an ipsp of course

• What are the required conditions for summated dipoles to record EEG?

  • Spatial summation
    
  • orientation of the dipoles need to be alligned
  • temporal summation
  • psp's have to occur at the same time
  • strength
  • you need hundreds of thousands collectively active neurons to pick up a signal

• How are electrodes used to record EEG?

  • Electrodes are connected to the scalp with conductive gel
    
  • the electrodes are often placed in a cap according to the 10/20 system
  • this system describes the arangement of the electrode 
  • the letters describe the lobes from front to back with a central line in the middle.
  • the numbers describe the location of the electrode within the coronal line, the higher the number the more lateral the electrode. Also uneven numbers are over the left hemisphere and even over the right

• What are two additional devices necessary to record EEG signals?

  • An amplifier; EEG signals often have a really low amplitude, the amplifier boosts recorded activity so it becomes more visible.
    
  • an analog to digital converter; This device translates the ongoing voltage difference of each electrode and stores it with a timeline in a file.

• In an experimental setting, how many averaging moments are there when processing the data?

  • One average moment to isolate the ERP in a subject.
    
  • a second averaging moment to gain the average ERP of a condition.
  • when doing the statistical analysis you use the ERP's of the individuals though.

• How can ERP data be displayed?

  All displays have in common;
  

  • time on the x-axis
  • voltage on the y-axis
  • often, negative upwards

  in 3d displays; time voltage, space
  

  • a map of the electrodes placement is shown
  • the ERP of a specific timepoint is shown per electrode

  in 2d displays average over space, time, voltage
  
  

  • two locations with each a few electrodes are compared
  • graph show the averages of these electrode on time and voltage

  topographical heat mappings are also used sometimes.

• How are ERP components labeled?

  • P or N indicate positive or negative
    
  • they can be numbered orderly; P2 comes after P1
  • or labeled in latency; P300 is a positive peak around 300 ms after stimulus onset.
  • they can have designated names; mismatch negativity, error-related negativity

• What does ERP polarity show?

  • ERP polarity does not represent excitation or inhibition.
    
  • it is in fact not really meaningfull
  • mostly caused by the orientation of the dipoles