When Do Infants Begin To Discriminate Pain From Touch?

in medicine, biology

How early can a human brain differentiate painful stimuli from gentle touches? According to a new study, brain wiring necessary to discriminate between a touch and a painful stimulus is in place from 35-37 weeks of gestation in the human brain.

In this study the authors have explored the changes in brain activity during the maturation of pain and touch discrimination in the preterm infant.  Brain activation by tactile and painful stimulation occurs from an early preterm stage but there is a shift in the pattern and specificity of the response with age.

The study was recently published in the peer-reviewed journal Current Biology.

infant pain sensation and gestation age
Nonspecific neuronal bursts recorded in a preterm infant
(34 weeks gestational age) following touch of the heel (dashed line).
Image credit: Dr. Lorenzo Fabrizi

Dr. Lorenzo Fabrizi, lead author of the paper from University College London Neuroscience, Physiology and Pharmacology, said: "We are asking a fundamental question about human development in this study – when do babies start to distinguish between sensations? In very young brains all stimulations are followed by 'bursts' of activity, but at a critical time in development babies start to respond with activity specific to the type of stimulation."

Dr. Fabrizi added: "Of course, babies cannot tell us how they feel, so it is impossible to know what babies actually experience. We cannot say that before this change in brain activity they don't feel pain."

When and how infants begin to discriminate pain from gentle touch is a fundamental question in neuroscience. However, little is known about the development of the necessary prerequisites in the human brain.

The pain stimulus, in the study, was a heel prick which is a customary practice used for collecting blood from new borns.  The researchers performed a light tendon tapping against the heal of the infants as the tactile stimulus. Brain neuronal activity was recorded using electroencephalogram (EEG). They studied 46 infants aged 28–45 weeks of gestation.

At early stages of brain development, less than 35 weeks gestation, the dominant response to both touch and painful lance of the heel was an increased incidence of nonspecific neuronal bursts. At later stages of brain development, after 35–37 weeks gestation, the dominant response was quite different: touch and lance of the heel  evoked characteristic activities, which were completely separable for the two forms of stimulation.

The results suggest that specific neural circuits necessary for mature discrimination between touch and pain seem to emerge from 35-37 weeks of gestation in the human brain.   

Source Article:  A Shift in Sensory Processing that Enables the Developing Human Brain to Discriminate Touch from Pain.  Lorenzo Fabrizi, Rebeccah Slater, Alan Worley, Judith Meek, Stewart Boyd, Sofia Olhede and Maria Fitzgerald. Current Biology (2011), doi:10.1016/j.cub.2011.08.010. Available online 8 September 2011.


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