Skip to main content icon/video/no-internet
icon backReturn to Entries

Tuning Curves

The neurons within each sensory system must collectively encode the vast ranges of stimulus information that are environmentally relevant to the organism. A ubiquitous characteristic of neurons in all sensory systems, however, is their sensitivity to a wide range of stimulus parameters. That is, no single neuron is so selective that it is sensitive to just one single stimulus value. For example, in the auditory system, there will be no neuron that responds only to, say, middle C (∼262 hertz [Hz]) and no other sound frequencies. In order for each of the sensory systems to encode the ranges of possible stimulus parameters, the neurons comprising those systems divvy up the range such that each neuron exhibits differing selectivity, but over restricted ranges of those stimuli. For example, in the auditory system, the responses of neurons are often jointly sensitive to sound frequency and intensity, with different neurons encoding different ranges of frequency and intensity. The range of frequencies over which an auditory neuron is responsive is indicated by its tuning curve. In the visual system, peripheral neurons are differentially selective for the spatial location, luminance, and wavelength of the stimulus. This entry examines the concept of the tuning curve, which is an experimental measure of the selectivity of neurons in sensory systems to one or more stimulus parameters.

Figure 1 Example of a Tuning Curve

None
Notes: (a) The experimentally measured response of an auditory neuron in terms of the number of sound-evoked action potentials is determined as a joint function of two different stimulus parameters, frequency (kilohertz [kHz]) and intensity (sound pressure level in decibels [dB SPL]). (b) Tuning curve for sound frequency given a fixed value of intensity. Tuning curves are shown for two values of sound intensity in panel a (corresponding to dashed lines a and b). (c) Tuning curves that result from two different constant criterion values of the number of action potentials in panel (a) (corresponding to lines A and B).

Measuring Tuning Curves

Figure 1 shows an example of how tuning curves are typically measured experimentally. Tuning curves can be measured as a function of one stimulus parameter or jointly as a function of two stimulus parameters. Here is a concrete example from the auditory system where tuning curves are often determined by measuring the number of action potentials a neuron fires (ordinate of Figure 1a) while varying the frequency (parameter of Figure 1a) and the intensity (abscissa of Figure 1a) of sounds presented to the ears. In many cases, the “responses” (action potentials in the current example) of the sensory systems being studied are related monotonically to monotonic increases in at least one stimulus parameter. This is particularly true for neurons or receptors at the most peripheral levels of a system.

It is important to keep in mind that quality and the quantity of the “response” being measured experimentally in the generation of a tuning curve can be of many different types. Most common of these is the number of action potentials a neuron under study fires in response to the presentation of a stimulus, such as in the example in Figure 1. The intracellular voltage (or current) potential of peripheral sensory receptors (e.g., hair cells, pho-toreceptors) and central neurons can also be used. These are just a few common types of responses that are measured in the generation of tuning curves.

...

  • Loading...
locked icon

Sign in to access this content

Get a 30 day FREE TRIAL

  • Watch videos from a variety of sources bringing classroom topics to life
  • Read modern, diverse business cases
  • Explore hundreds of books and reference titles

Read next

More like this

Sage Recommends

We found other relevant content for you on other Sage platforms.

close

Have you created a personal profile? Login or create a profile so that you can save clips, playlists and searches

close
close
close Signed In to profile You are signed in as:
close
Logged in Institution Institution