LOSS OF FUNCTIONAL HEMISPHERIC-ASYMMETRY IN ALZHEIMERS DEMENTIA ASSESSED WITH NEAR-INFRARED SPECTROSCOPY

In a total of 10 patients with dementia of the Alzheimer-type (DAT) an d in 10 healthy controls near-infrared spectroscopy (NIRS), a new non- invasive optical method, was used to measure the changes of concentrat ions of oxy-(O2HB) and deoxyhemoglobin (HHB) in left and right hemisph eric prefrontal brain tissue areas during performance of the Verbal Fl uency Test (VFT). On a neuropsychological level, the healthy subjects performed better in the VFT than patients with DAT. Statistical analys is of the relative concentrations of O,HB and HHB measured with NIRS d uring performance of the VFT revealed a significant interaction of the hemispheric effects with the diagnosis. A possible interpretation of this finding is that a good performance in the VFT relies on a predomi nantly left hemispheric activation observed in controls, whereas a low number of correct responses is associated with a loss of this asymmet ric activation in patients with DAT. Although both, patients and contr ols, performed better in the category version of the VFT, the metaboli c effects of this task were significantly less pronounced than in the letter version. This indicates that different energy demands, accordin g to the type of access to the memory stores, may be interpreted as th e result of a less energy-demanding access to categorically stored inf ormation and adds further evidence to the view that memory departments in humans are organized according to categorical principles.