The mean cognitive symptoms are:

 

• Dementia

• Abnormal awareness and perception

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Cognitive decline occurs in all individuals affected. Slowness of thought processes, difficulties in knowledge manipulation, forgetfulness and impaired visuopatial abilities might occur in majority of patients. Cognitive symptoms appear prior to motor symptoms. Early cognitive symtoms are loss of mental flexibility and planning and disability for doing sequential activities, memory deficits and impairment at retrieval of information. Also, distractibility occurs because of attention disturbance. The language manipulation becomes a difficulty in late stages. Lack of awareness is a very common symtom.