Difficulty with learning of exercise instructions associated with 'working memory' dysfunction and frontal glucose...

We present a patient with no dementia, depression or apathy, who had difficulty in learning self-exercise instructions. The patient was an 80-year-old right-handed woman who was admitted to a rehabilitation unit to receive postoperative rehabilitation after a femoral neck fracture. She was instructed quadriceps isometric exercises to perform 10 repetitions and to hold each stretch for 10 s. She performed the exercise correctly with motivation, but she had difficulty in learning the number of repetitions and the duration of each stretch. She had no history of cerebrovascular accident and the neurological examination was normal. Neuropsychological testing, MRI and (18)F-fluoro- D-glucose-positron emission tomography (FDG-PET) were performed to examine the neural mechanisms associated with this difficulty in learning instructions. Neuropsychological tests revealed dysfunction of working memory while other cognitive domains were relatively preserved. Her neuropsychological tests scores were (1) Mini-Mental State Examination: 24 (mild cognitive impairment), (2) Geriatric Depression Scale-15: 2 (no depression), (3) Apathy Scale: 2 (no apathy), (4) digit span forward: 5 (normal), (5) digit span backward: 2 (impaired), (6) visuospatial span forward: 4 (normal), (7) visuospatial span backward: 2 (impaired), (8) frontal assessment battery: 11 (normal), (9) Weigl test: 0 (impaired), (10) trail making test A: 52 s (normal), (11) train making test B: failed (impaired). T2-weighted and fluid-attenuated inversion recovery MRI showed high signal-intensity lesions in the cerebral deep white matter. FDG-PET revealed hypometabolic areas in the bilateral frontal lobes, particularly in the bilateral dorsolateral frontal area, anterior cingulate cortex and orbitofrontal cortex. One of the possible neural mechanisms underlying the learning difficulties in this patient may have been partial blockage of the cingulofrontal network by deep white matter lesions.