Reading problems stem from brain processing of sounds
Reading problems stem at least in part from a fundamental defect in the brain's ability to process sounds, according to new research.
American neuroscientists say they have the first direct evidence that reading difficulties are correlated with abnormal brain-cell responses to brief, rapidly successive sounds, making it much harder to make the "mental leap" to recognising the sound parts of words and translating them to written letters.
The findings indicate a basic problem in "signal reception" that persists through life in affected individuals, says the study's leading author, Dr Michael Merzenich, from the University of California, San Francisco's Keck Center for Integrative Neuroscience.
The representation in the brain of the sound parts of words was "weaker and less salient" in these people than in competent readers, said Dr Merzenich, whose paper is published in today's Proceedings of the National Academy of Sciences.
He believes those affected are therefore "not delivering the normal forms of representation of the separable sound parts of words to the regions of the brain involved in speech perception and reading."
The team reached their conclusion after comparing the sound-processing powers of poor readers with normal readers using a non-invasive brain imaging technique which measures the tiny magnetic fields produced by electric currents in nerve cells.
The magnetic fields in the part of the brain that processes sounds - the auditory cortex - were significantly different in the poor readers and correlated strongly with poor performance on a task requiring detection, recognition and discrimination of rapidly-presented paired sounds.
While some scientists had argued that difficulty distinguishing word sounds meant children were destined to have problems learning to read, the defect was thought to account for only a small proportion of adults who found reading hard.
"To the contrary, we have seen that most poor readers and most language-impaired children share these same fundamental listening and brain processing abnormalities," Dr Merzenich said.
But the findings don't rule out the possibility that higher levels of brain processing can also impair the ability to break words into their component sounds, and that general memory and attention difficulties can also play a role.