What Is Lateral Inhibition? Definition and Examples

Neuron Network
Neuron Network.

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Lateral inhibition is the process by which stimulated neurons inhibit the activity of nearby neurons. In lateral inhibition, nerve signals to neighboring neurons (positioned laterally to the excited neurons) are diminished. Lateral inhibition enables the brain to manage environmental input and avoid information overload. By dampening the action of some sensory input and enhancing the action of others, lateral inhibition helps to sharpen our sense perception of sight, sound, touch, and smell.

Key Takeaways: Lateral Inhibition

  • Lateral inhibition involves the suppression of neurons by other neurons. Stimulated neurons inhibit the activity of nearby neurons, which helps sharpen our sense perception.
  • Visual inhibition enhances edge perception and increases contrast in visual images.
  • Tactile inhibition enhances perception of pressure against the skin.
  • Auditory inhibition enhances sound contrast and sharpens sound perception.

Neuron Basics

Neurons are nervous system cells that send, receive, and interpret information from all parts of the body. The main components of a neuron are the cell body, axons, and dendrites. Dendrites extend from the neuron and receive signals from other neurons, the cell body is the processing center of a neuron, and axons are long nerve processes that branch out at their terminal ends to convey signals to other neurons.

Nerve Impulse
The conduction of the action potential across a myelinated and an unmyelinated axon. Encyclopaedia Britannica/UIG/Getty Images

Neurons communicate information through nerve impulses, or action potentials. Nerve impulses are received at neuronal dendrites, passed through the cell body, and carried along the axon to terminal branches. While neurons are close together, they don't actually touch but are separated by a gap called a synaptic cleft. Signals are transmitted from the pre-synaptic neuron to the post-synaptic neuron by chemical messengers called neurotransmitters. One neuron can make connections with thousands of other cells at synapses creating a vast neural network. 

How Lateral Inhibition Works

Lateral Inhibition
In lateral inhibition, the activation of a principal cell recruits an interneuron, which, in turn, suppresses the activity of surrounding principal cells.  Adapted from work by Peter Jonas and Gyorgy Buzsaki/Scholarpedia/CC BY-SA 3.0

In lateral inhibition, some neurons are stimulated to a greater degree than others. A highly stimulated neuron (principal neuron) releases excitatory neurotransmitters to neurons along a particular path. At the same time, the highly stimulated principal neuron activates interneurons in the brain that inhibit excitation of laterally positioned cells. Interneurons are nerve cells that facilitate communication between the central nervous system and motor or sensory neurons. This activity creates greater contrast among various stimuli and results in greater focus on a vivid stimulus. Lateral inhibition occurs in sensory systems of the body including olfactory, visual, tactile, and auditory systems.

Visual Inhibition

Lateral inhibition occurs in cells of the retina resulting in enhancement of edges and increased contrast in visual images. This type of lateral inhibition was discovered by Ernst Mach, who explained the visual illusion now known as Mach bands in 1865. In this illusion, differently shaded panels placed next to each other appear lighter or darker at the transitions despite uniform color within a panel. Panels appears lighter at the border with a darker panel (left side) and darker at the border with a lighter panel (right side).

Mach Bands
Mach Bands. Copyright - Evelyn Bailey

The darker and lighter bands at the transitions are not really there but are the result of lateral inhibition. Retinal cells of the eye receiving greater stimulation inhibit surrounding cells to a greater degree than cells receiving less intense stimulation. Light receptors receiving input from the lighter side of the edges produce a stronger visual response than receptors receiving input from the darker side. This action serves to enhance contrast at the borders making the edges more pronounced.

Simultaneous contrast is also the result of lateral inhibition. In simultaneous contrast, the brightness of a background affects the perception of brightness of a stimulus. The same stimulus appears lighter against a dark background and darker against a lighter background.

Simultaneous Contrast
The two bars are the same shade of gray throughout, but they appear lighter on the top (against a dark background) than on the bottom (against a light background). Shi V, et al./PeerJ 1:e146/CC BY 3.0  

In the image above, two rectangles of different widths and uniform in color (gray) are set against a background with a gradient of dark to light from the top to the bottom. Both rectangles appear lighter at the top and darker at the bottom. Due to lateral inhibition, light from the top portion of each rectangle (against a darker background) produces a stronger neuronal response in the brain than the same light from the lower portions of the rectangles (against a lighter background).

Tactile Inhibition

Lateral inhibition also occurs in tactile, or somatosensory perception. Touch sensations are perceived by activation of neural receptors in the skin. The skin has multiple receptors that sense applied pressure. Lateral inhibition enhances the contrast between stronger and weaker touch signals. Stronger signals (at the point of contact) inhibit neighboring cells to a greater degree than weaker signals (peripheral to the point of contact). This activity allows the brain to determine the exact point of contact. Areas of the body with greater touch acuity, such as the fingertips and tongue, have a smaller receptive field and a greater concentration of sensory receptors.

Auditory Inhibition

Lateral inhibition is thought to play a role in hearing and the auditory pathway of the brain. Auditory signals travel from the cochlea in the inner ear to the auditory cortex of the brain's temporal lobes. Different auditory cells respond to sounds at specific frequencies more effectively. Auditory neurons receiving greater stimulation from sounds at a certain frequency can inhibit other neurons receiving less stimulation from sounds at a different frequency. This inhibition in proportion to stimulation helps to improve contrast and sharpen sound perception. Studies also suggest that lateral inhibition is stronger from low to high frequencies and helps to adjust neuron activity in the cochlea.

Sources

  • Bekesy, G. Von. "Mach Band Type Lateral Inhibition in Different Sense Organs." The Journal of General Physiology, vol. 50, no. 3, 1967, pp. 519–532., doi:10.1085/jgp.50.3.519.
  • Fuchs, Jannon L., and Paul B. Drown. "Two-Point Discriminability: Relation to Properties of the Somatosensory System." Somatosensory Research, vol. 2, no. 2, 1984, pp. 163–169., doi:10.1080/07367244.1984.11800556. 
  • Jonas, Peter, and Gyorgy Buzsaki. "Neural Inhibition." Scholarpedia, www.scholarpedia.org/article/Neural_inhibition.
  • Okamoto, Hidehiko, et al. "Asymmetric Lateral Inhibitory Neural Activity in the Auditory System: a Magnetoencephalographic Study." BMC Neuroscience, vol. 8, no. 1, 2007, p. 33., doi:10.1186/1471-2202-8-33.
  • Shi, Veronica, et al. "Effect of Stimulus Width on Simultaneous Contrast." PeerJ, vol. 1, 2013, doi:10.7717/peerj.146.