The scratch reflex is an automatic response to the activation of sensory neurons located on the surface of the body. Sensory neurons can be activated via stimulation, such as a parasite on the body, but can also be activated by responding to a chemical stimulus that produces an itching sensation. During a scratch reflex, a limb reaches toward and rubs against the site on the body surface that has been stimulated. The scratch reflex has been extensively studied to understand the functioning of neural networks in vertebrates. Despite decades of research, key aspects of the scratch reflex are still unknown, such as the neural mechanisms by which the reflex is terminated.

Most dogs will exhibit a scratch reflex when they are stimulated in the saddle region, which consists of the belly, sides, flanks, and back. These are the most common sites, but stimulation anywhere may be able to produce the reflex, such as the chest, ears, and even paws. Once stimulation of this area begins, the dog will begin to rhythmically "twitch" or "kick" their hind legs in an attempt to rid itself of the "irritant". Typically, only one of the hind legs will exhibit this reflex at a given time, however, it is possible for both legs to undergo the reflex at the same time. The intensity and rhythm of the reflex will vary depending on the intensity and speed of the stimulation.

The scratch reflex can commonly be triggered through various stimulations such as scratching, brushing, rubbing, or tapping a dog, although some techniques work better than others. For example, a majority of dogs will exhibit the reflex when scratched with fingernails, while only some with a stronger reflex might react to a lighter tapping.

Allergies and itchiness often play a role in the scratch reflex, with dogs who are already itchy before the additional stimulation often producing a stronger reflex than other dogs. It is common for dogs with flea infestations to have a strong reflex when stimulated at the base of the tail, due to the itchiness caused by the fleas.

A number of animal models have been used to study, understand and characterize the scratch reflex. These models include the turtle, cat, frog, dog, and a variety of other vertebrates. In these studies, researchers made use of spinal preparations, which involve a complete transection of the animal's spinal cord prior to experimentation. Such preparations are used because the scratch reflex can be elicited and produced without the involvement of supraspinal structures. Researchers focused predominantly on investigating spinal cord neural circuitry responsible for the generation of the scratch reflex, limiting the system of study.

In studies of spinal preparations, researchers have experimented with using preparations both with and without movement-related sensory inputs. In preparations with movement-related sensory inputs, the muscles and the motor neuron outputs to muscles are left intact, allowing sensory feedback from the moving limb. In preparations without movement-related sensory input, one of three strategies is used:

Electromyographic (EMG) and electroneurographic (ENG) techniques are used to monitor and record from animals during experiments. EMG recordings are used to record electrical activity directly from muscles. ENG recordings are used to record electrical activity from motor neurons and spinal cord neurons. These techniques have enabled researchers to understand the neural circuitry of the scratch reflex on a single-cell level.

The scratch reflex is generally a rhythmic response. Results from animal studies have indicated that spinal neural networks are known as central pattern generators (CPGs) are responsible for the generation and maintenance of the scratch reflex. One feature of the scratch reflex is that supraspinal structures are not necessary for the generation of the reflex. The scratch response is programmed into the spinal cord and can be produced in spinal animals.^{[citation needed]}