- Scientists use reaction time to measure neurological deficits related to prenatal alcohol exposure.
- One signal and response is called simple reaction time (SRT).
- Two or more signals and responses are called choice reaction time (CRT).
- Children who were prenatally exposed to alcohol, yet do not have Fetal Alcohol Syndrome, have slower information processing and motor responses to CRT tasks.
Many individuals who were prenatally exposed to alcohol may not meet the criteria for Fetal Alcohol Syndrome, but nevertheless suffer from a wide range of neurobehavioral effects such as hyperactivity, learning and memory deficits, attention problems, and reductions in IQ. One measure used to examine neurological deficits is reaction time (RT), defined as the interval between perceiving a signal and physically responding to it. A study in the September issue of Alcoholism: Clinical & Experimental Research uses various RT tasks to closely examine information processing and motor responses in children who were prenatally exposed to alcohol.
"Reaction time is a measure of the delay in time that occurs between perceiving a signal, such as a light being turned on, and making a physical response to the signal, such as lifting a finger or hand from an electronic switch," explained Roger W. Simmons, professor of exercise and nutritional sciences at San Diego State University - San Diego and lead author of the study. "Since most of the elapsed time between the signal and the response is taken up with the brain processing the signal and deciding what motor response to make, RT is considered to be a generalized measure of decision making."
When one signal and response are used, it is called simple reaction time (SRT). When two or more signals and responses are used, it is called choice reaction time (CRT). As the number of signals and responses increases, the amount of information to be processed also increases. This, in turn, involves greater decision-making skills and is reflected in longer reaction times.
For this study, researchers compared two groups of children: 11 (10 male, 1 female) with confirmed prenatal alcohol exposure, and 14 nonexposed children (13 males, 1 female). All of the children completed 20 trials of both SRT and CRT tasks. Muscle activity was recorded from the bicep brachii muscle of each arm using electromyography to measure reaction times.
"Our study showed that for SRT tasks, when the information-processing load is relatively small," said Simmons, "there was no significant difference in reaction time between the children with prenatal alcohol exposure and the control children. However, when the information load increased during CRT tasks, alcohol-exposed children had slower reaction times. This is consistent with the notion that alcohol exposure results in brain damage, which, in turn, impairs information processing and produces a slower CRT."
"It is significant that these findings persisted after the investigators controlled for IQ deficits," noted Sandra W. Jacobson, professor and director of Therapy Research and Resident Training at Wayne State University School of Medicine. "Otherwise, it could be argued that the processing speed deficit was merely another manifestation of the children's poorer IQ. Instead, what is shown here is that even when you control for IQ, the children who are heavily exposed process information and react more slowly." These deficits, she added, likely reflect damage to numerous regions of the brain.
"Another significant and innovative aspect of this report," said Jacobson, "is that the investigators used a state-of-the-art paradigm, one in which they were able to further separate premotor from motor reaction times in children known to have been heavily exposed to alcohol during pregnancy and compare their performance to that of matched controls."
Premotor reaction time reflects the amount of time necessary to perceive a signal and generate a motor plan. During a CRT task, premotor RT also involves the time taken to discriminate between signals. In contrast, motor reaction time reflects the time taken to convey the motor plan from the brain to the muscles involved in making the response.
"The purpose of splitting reaction time into these two components," explained Simmons, "is that it allows us to measure the time required for information processing, called central activity, without the influence of the time required to convey the action plan from the brain to the muscles, called peripheral activity."
The children with prenatal exposure to alcohol had slower premotor RTs during the CRT task. This means they were not able to process information as quickly as the control children when they had to respond to more than one signal. During SRT and CRT tasks, the alcohol-exposed children also had slower motor RTs. This indicates that prenatal alcohol exposure also had a negative impact on the peripheral processes involved in conveying the action plan from the brain to the muscles.
"Young children typically respond with less accuracy or speed than older children or adults on a variety of motor skills," said Simmons. "Our study confirmed this for both groups using the premotor and motor components of reaction time. The younger children were unable to process information at the same speed as the older children, and were also slower in conveying the action plan from the brain to the muscle. However, these differences were more acute within the alcohol group. Furthermore, the performance of the older alcohol-exposed children was often very similar to the performance of the younger, nonexposed children. Collectively, these results indicate a lack of development in both central and peripheral structures to the extent that it significantly affects both premotor and motor reaction time. We believe that exposure to alcohol results in damage to the brain and peripheral structures, which results in timing deficits."
Co-authors of the Alcoholism: Clinical & Experimental Research paper included: Tara Wass of the Department of Child & Family Studies at the University of Tennessee, and of the Alcohol Research Center, Department of Neuropharmacology, The Scripps Research Institute; and Jennifer D. Thomas and Edward P. Riley of the Center for Behavioral Teratology in the Department of Psychology at San Diego State University - San Diego. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.