Brain Pathway Behind Placebo Effect Disclosed!

Information about expectations — the driver of the placebo effect — travels from the cortex to groups of cells in the brainstem, which then modulate pain signals in the spinal cord.

Your expectations can control the intensity of your pain perception, although it is not all in your head. Scientists finally decipher the mystery behind the placebo effect.

It was found that the driver of the placebo effect – information about expectations travels from the cortex to groups of cells in the brainstem, which then modulate pain signals in the spinal cord, as per a study "Brainstem Mechanisms of Pain Modulation: a Within-Subjects 7T fMRI Study of Placebo Analgesic and Nocebo Hyperalgesic Responses", published in JNeurosci.

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‘New study finds that information about expectations — the driver of the placebo effect — travels from the cortex to groups of cells in the brainstem, which then modulate pain signals in the spinal cord.’

The study team measured the activity of the brainstem using high-resolution fMRI in participants as they rated the pain of a hot stimulus applied to their arm.

The Placebo Effect

The participants were conditioned to think of three types of cream to have been applied to their arms. They are – a pain-relieving cream with lidocaine, a heat-intensifying cream with capsaicin, and Vaseline.

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However, in reality, all three creams were Vaseline, and any perceived differences in pain came from the placebo or nocebo effect (imagined increases in pain).

The activity in the same brainstem circuit was influenced by placebo and nocebo effects but in opposite ways.

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The strength of the placebo effect was linked to increased activity in an area called the rostral ventromedial medulla and decreased activity in a nucleus called the periaqueductal gray; the nocebo effect induced the opposite change.

Hence, these results reveal the role of the brainstem in pain modulation and may offer a route for future treatments of chronic pain.

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Source-Medindia