Others include difficulty with technology and new tasks, and personality changes such as becoming more withdrawn and less talkative.

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"Character and personality changes are fairly pervasive with motor vehicle accidents, " he said, but added that the brain was changeable or "plastic" and repaired itself over time to varying extents.

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Have you noticed any personality changes, including increased irritability?

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Rankin and her team focused on a a specific type of neurodegenerative disease called frontotemporal dementia, or FTD, a group of disorders in which patients can experience behavioral symptoms such as personality changes, a loss of inhibition and social tact as well as language difficulties, such as an inability to understand words.

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Some straight spouses have spoken of deep changes to their personality or habits: Developing tastes for foods they never liked before or losing interest in formerly favorite activities.

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Sudden changes in mood or personality, visual hallucinations and alternations in smell, taste or tactile senses could signal a brain tumor or other abnormality.

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The focus recently has been on trying to pin down the details of the neutrino's split personality: How far it travels before it changes from one type into another, and which types change into which and with what frequency.

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In other conditions in which social problems aren't the main symptoms, including dementia, depression and schizophrenia, early clues may come from changes to a person's normal personality, such as becoming less friendly, understanding or attentive, or more paranoid.

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