Leading researchers in colic and infant development say that a simple analysis of babies' cries can provide a window into their neurological and medical status.

In a research review in the current issue of Mental Retardation and Developmental Disabilities, Linda LaGasse, PhD, and Barry Lester, PhD, with the Bradley Hasbro Children's Research Center (BHCRC) and Brown Medical School looked at previous studies that analyzed the acoustics of a baby's cry. The authors cite the characteristics of a cry that can indicate problems in a baby's nervous system, as well as sudden infant death syndrome (SIDS). In addition, they cite the importance of how parents react to their squalling offspring.

"The cry signal has enormous potential diagnostic value; for example, very high pitched cries can tell us that something may be wrong with the infant, so the cry signal can be an early warning that leads to further neurological testing," says LaGasse.

Overall, studies have repeatedly shown that infants at medical risk (like premature babies), and infants who have been exposed to lead or drugs, cry at a higher and more variable frequency than normal, but at lower amplitude, and with short utterances. These types of cry signals point toward a capacity problem in the respiratory system as well as an increased tension and instability of neural control of the vocal tract.

"Given the results of earlier studies relating cry characteristics to known neurological compromise, these findings suggest that at-risk infants have undetected neurological damage and that cry analysis may be able to identify these infants when no other symptoms are present," says Lester.

In looking at cry analyses on sudden infant death syndrome, researchers found that high resonance and changes in the cry mode were consistent markers associated with SIDS. Resonance is the characteristic of a sound's richness and depth that help humans distinguish a C note on a piano versus a guitar, and mode changes are noisy, broken-sounding cries that indicate poor neural control of the vocal track.

While someone might be able to point out a noisy cry, there is little evidence that a high resonance is distinguishable from a low resonance by an untrained listener.

"Instead, resonance is identified by a computerized analysis of the cry signal in the studies cited in the paper -- this is why a detailed analysis of the cry signal is an important part of understanding the 'full message' of the cry," says LaGasse.

The authors also note that parents tend to understand the nature of their babies' cries well, and stress the importance of parental reaction to cries.

"Parents can usually tell the difference between pain and non-pain cries which guides the urgency of their care taking, and helps parents deal with infants with colic," says LaGasse.

But parent perception of their infant's cry may be affected by conditions such as depression or age of parent which can lead to action or nonaction which may be out of sync with the infant's needs. The most extreme case is "shaken baby syndrome" where the cry triggers aggression rather than concern in the caretaker.

Lester and LaGasse say that clinicians should be aware of how parents respond (or don't respond) to their baby's crying, especially in light of the high prevalence of depression in young mothers.

"Helping parents to correctly interpret their infants' cries can optimize development particularly in high risk infants who may have atypical signals or high risk parents who may misperceive a normal cry," they write.