Language Localization with fMRI
Damage to areas of the brain that process language can result in a loss of the ability to understand or produce speech. As the brain repairs itself, language may reorganize in other, undamaged parts of the cortex. This reorganization can be "local", occurring in healthy tissue adjacent to damaged language areas (intrahemispheric), or it may involve transfer of language functions to the opposite hemisphere of the brain (interhemispheric). In collaboration with colleagues at Temple University and Thomas Jefferson University, we are developing and evaluating functional magnetic resonance imaging (fMRI) protocols for mapping this reorganization of language. We are correlating the fMRI findings with other measures of brain lateralization and cerebral dominance for language.
Neuroplasticity: Language Recovery in Aphasia
Aphasia is a disorder of speech production and understanding that results from damage to language areas of the brain. The traditional treatment is speech/language therapy. However, recent studies suggest that recovery of language may also be enhanced by certain medications which, when combined with behavioral therapy, may promote neuroplasticity. In order to understand the nature of this effect, we are conducting double-blind, placebo-controlled, crossover studies to examine the effects of low doses of dextroamphetamine on the ability of patients with aphasia to attend to and process language. We are examining the effects of the medication on behavioral performance and as well as changes that occur in brain activation, as reflected in event-related electrical brain potentials (see left) and fMRI.
Cerebral Dominance for Language
For 95 to 99% of right-handed individuals, the left hemisphere of the brain is dominant for processing language. Dichotic listening is a widely used behavioral method to assess language lateralization that involves the simultaneous presentation of pairs of contrasting stimuli, one in the right ear and one in the left ear. By studying accuracy of recall from the right or left ear, information can be gained about functional asymmetries in auditory processing related to hemispheric specialization of function. Given that the left cerebral hemisphere in humans is particularly proﬁcient at processing speech stimuli, listeners show a right ear advantage (REA) in recall of dichotically presented speech. We are interested in how well different dichotic listening techniques lateralize language in comparison to newly developed fMRI measures of brain activation.
Language Regression in Childhood
For most children, the ability to understand and produce speech unfolds naturally in the first 18 months of life and effortlessly increases in complexity throughout childhood. However, some children demonstrate a different developmental tradjectory, showing good initial gains and then a loss of previously acquired skills. This type of regression occurs in approximately 30 percent of children diagnosed with Autistic Spectrum Disorders (ASD). We are exploring some of the potential causes of language regression in children and their implications for treatment.
Steady-State Evoked Potentials
Brain electrical activity recorded from the scalp provides a millisecond by millisecond index of neural events underlying the processing of information. The brain contains neurons in the auditory cortex that are specialized for detecting variations in sound. These cells are important for analyzing complex sounds and distinguishing between different consonants. We have shown that when these cells are damaged, the result is a problem in comprehending language. In the lab, we are utilizing a novel technique called “steady-state potentials” to record the neural activity generated in the brain as the listener hears sounds that are changing rapidly. We are conducting a cross-sectional analysis of steady-state evoked responses to rapid frequency changes in sound in normal school-aged children of different ages and children with language problems.
Landau-Kleffner syndrome (LKS) is a disorder of childhood onset characterized by an acquired aphasia that emerges in association with epileptic or epileptiform electroencephalographic abnormalities. The loss of language occurs after a period of normal development and typically results in severe impairment of both the comprehension and production of speech. Electroencephalograms (EEGs) recorded around the time of the regression regularly demonstrate severe epileptiform abnormalities, that may be most evident during sleep. This abnormal brain electrical activity is thought to play a causal role in the aphasia by disrupting the function of cortical networks required for normal language function. We have a special interest in defining the underlying basis of the disorder and the most appropriate treatment.