2008 The Brain's code

2008 The Brain's code - The Brain's Code Coding and...

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The Brain’s Code
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Coding and decoding stimuli delivered to the skin • Location • Modality • Magnitude • Duration
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Sensory neurons in the dorsal root ganglion transmit information from the skin to the spinal cord
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Stimulus intensity Number of activated sensory neurons and their discharge frequency Definitions: Receptive field of a neuron is region of body which when activated by its adequate stimulus causes the neuron to change its level of firing.
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Activity of sensory neurons altered by stimuli in receptive field : number of neurons activated is proportional to stimulus intensity (population code)
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Discharge frequency of sensory neurons also measures stimulus intensity: stimulus intensity Æ discharge frequency Frequency modulation
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Number of active fibers and discharge frequency is decoded centrally by spatial and temporal summation of chemical synaptic potentials Spatial summation Temporal summation
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Temporal and spatial summation • Temporal and spatial summation occur because the synaptic depolarization produced by an impulse lasts relatively long (about 20 ms). • This permits summation of synaptic potentials produced by other inputs or by successive impulses in the same fiber. • Synaptic potentials can summate; action potentials cannot.
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Stimulus duration Coded by duration of discharge in slowly adapting fibers
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Slowly adapting receptor signals stimulus magnitude; rapidly adapting receptor signals stimulus onset/ velocity. Receptor specialization responsible for adaptation properties
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Stimulus modality Sensory neurons have different adequate stimulus : some respond to mechanical stimuli; others to heat, to cold, etc.
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The skin contains distinct receptor types
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2008 The Brain's code - The Brain's Code Coding and...

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