2007 Sensory Physiology

Stimulus Location


Stimulus intensity
To understand the lateral inhibition process, start with intensity coding:
  • the primary afferent fibre whose receptive field centre is closest to the point of stimulation will produce more action potentials than those on the periphery (e.g., the green fibre in the diagram has a greater action potential frequency than the blue fibres)

Lateral inhibition process

S&G Figure 10.10

In this diagram the receptors and primary afferent fibres are located at the bottom of the diagram, the CNS (red box) at the top.

Within the CNS,

  • the primary afferent neurons are connected to inhibitory interneurons (pink and red cells) as well as to second order neurons that continue to carry the information along the primary sensory pathway (green and blue cells)
  • according to Dale's law, primary afferent neurons release excitatory neurotransmitter at each synapse (i.e., +ve response on inhibitory interneurons as well as on second order neurons) - the interneurons have a -ve response on adjacent second order neurons
  • action potentials in the second order neurons whose receptive fields are toward the periphery of the stimulus field (blue) are more strongly inhibited, and therefore produce fewer action potentials, than the cell with its receptive field in the centre (green)
Sensation vs. receptor activation

The net result is that --- within the CNS --- the area of sensation is less than the area of receptor activation, due to the areas of inhibition that flank the centre of stimulus.

  • another way of thinking about this is: lateral inhibition increases contrast between strong and weak signals

See also the discussion of ON/OFF cells in the retina.



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