In psychology, sensitization is a non-direct non-associative learning process where repeated exposure to a stimulus ends up in an increased reaction to that stimulus. Essentially, the subject becomes more sensitive to the stimulus as time goes on.
As an example, if you take your cat to the vet in the same car where he gets a big nasty shot in the arm, that cat might eventually associate that car with the pain of the shot, and highly resist going into the car. If you go to the bar every Friday night and repeatedly order a vodka cranberry, eventually you’ll get used to the idea of having no taste whatsoever and stop going out at all.
What is Sensitization in Psychology?
Sensitization is a fancy way of saying that when you’re repeatedly exposed to a stimulus, your response to it can become amplified.
This means that not only will you respond more strongly to the original stimulus, but you might also respond more strongly to other stimuli that are similar to it. For example, if you keep getting a painful injection, you might become more sensitive to loud noises as well.
Sensitization has been studied for a long time, with Eric Kandel being one of the pioneers in this field back in the 1960s and 1970s. He studied the gill withdrawal reflex in a seaslug called Aplysia, and found that by repeatedly pairing a painful electrical stimulus with a touch to the animal’s siphon, he could cause the gill withdrawal response to become stronger and more persistent. This sensitization effect lasted for several days and could even be triggered by a light touch to the siphon alone.
Kandel’s work was groundbreaking and helped us understand the neural basis of sensitization. In fact, his research was so influential that he was awarded the Nobel Prize in Physiology or Medicine in 2000!
Types of Sensitization in Psychology
Sensitization is a fascinating learning process that involves the progressive amplification of a response to a stimulus. In the brain, long-term potentiation or LTP occurs when the hippocampus is electrically or chemically stimulated, resulting in the strengthening of synaptic signals. This phenomenon is believed to underlie memory and learning.
On the other hand, central sensitization happens when nociceptive neurons in the spinal cord’s dorsal horns become sensitized due to peripheral tissue damage or inflammation. This type of sensitization is thought to be a possible cause of chronic pain conditions.
Researchers have observed that repeated exposure to painful stimuli can change the animal’s pain threshold and result in a stronger pain response. People who have had back surgery or newborns who have undergone circumcision without anesthesia may continue to feel pain even after the stimulus has been removed.
Kindling is another type of sensitization that occurs when hippocampal or amygdaloid neurons in the limbic system are repeatedly stimulated, leading to seizures in laboratory animals. This model has been suggested as a possible representation of temporal lobe epilepsy in humans. People with this condition often report negative effects such as anxiety and depression resulting from limbic dysfunction.
Drug sensitization, meanwhile, happens in drug addiction and is characterized by an increased effect of a drug after repeated doses. This is the opposite of drug tolerance and involves changes in brain mesolimbic dopamine transmission and the protein delta FosB inside mesolimbic neurons. Environmental stimuli associated with drug taking may also increase craving, contributing to addiction and increasing the risk of relapse in those attempting to quit.
What is Cross-Sensitization?
Cross-sensitization occurs when sensitization to a particular stimulus is generalized to other related stimuli, leading to a stronger response to both.
For instance, cross-sensitization has been observed in addictive drug use, where sensitization to one drug may result in cross-sensitization to other drugs in the same class, or even to natural rewards like sugar. In animals, this cross-sensitization has been seen between many different types of drugs of abuse, providing support for the gateway drug theory.
But cross-sensitization isn’t just limited to addiction.
It’s also been suggested as a causal or maintaining mechanism in a wide range of pathologies, including allergies, asthma, overactive bladder, fibromyalgia, multiple chemical sensitivity, and even psychological disorders like post-traumatic stress disorder, panic anxiety, and mood disorders. In these cases, repeated exposure to a stimulus can sensitize the body to respond more strongly, leading to chronic symptoms and even pathology.
Cross-sensitization is a fascinating phenomenon with implications for a variety of areas in biology and medicine.