In October 1932 Ravel suffered a blow to the head in a taxi accident. The injury was not thought serious at the time, but in a study for the "British Medical Journal" in 1988 the neurologist R. A. Henson concludes that it may have exacerbated an existing cerebral condition. As early as 1927 close friends had been concerned at Ravel's growing absent-mindedness, and within a year of the accident he started to experience symptoms suggesting aphasia. Before the accident he had begun work on music for a film, "Don Quixote" (1933), but he was unable to meet the production schedule, and Jacques Ibert wrote most of the score. Ravel completed three songs for baritone and orchestra intended for the film; they were published as "Don Quichotte à Dulcinée". The manuscript orchestral score is in Ravel's hand, but Lucien Garban and Manuel Rosenthal helped in transcription. Ravel composed no more after this. The exact nature of his illness is unknown. Experts have ruled out the possibility of a tumour, and have variously suggested frontotemporal dementia, Alzheimer's disease and Creutzfeldt–Jakob disease. Though no longer able to write music or perform, Ravel remained physically and socially active until his last months. Henson notes that Ravel preserved most or all his auditory imagery and could still hear music in his head.