Earlier this year, in a London hospital on a dark afternoon at the end of winter, a neurosurgeon asked me to spell ‘world’ backwards. Behind him, an image of my skull floated on a monitor. On one side of it, there was a milk-white gob of tumour. It looked about as big as a golf ball. He wanted me to spell the word backwards because I am left-handed, and because I have a tumour lodged in my right temporal lobe. ‘Are you right-handed or left-handed?’ is often the first question a neurologist will ask. From the answer, it is possible to get an idea of how someone’s brain is organised – in particular, which hemisphere is dominant in certain aspects of language processing. Brain function is cross-wired: if I wiggle my left foot, the instructions are issued from the right side of my brain. The same is true if I wink shutting my left eye – what I then see through my open right eye is processed by the left side of my brain.
In most brains, language function is also lateralised. For around 95 per cent of right-handers and 60 per cent of left-handers, the neurological hardware required for language cognition is located in the left hemisphere in the regions known as Wernicke’s Area, at the rear of the left temporal lobe, and Broca’s area, a little further forward in the left frontal lobe. If either is damaged, the implications for language expression and cognition can be serious and a degree of aphasia can result. In the most severe instances, words simply become meaningless. Those affected cannot read, write or talk coherently and often compensate by inventing elaborate neologisms and making educated guesses based on partial memories from a time when words had meaning (saying ‘chair’ for ‘table’ or ‘spoon’ for ‘fork’).
If the right hemisphere is damaged, language cognition tends to be affected in a different way. The right hemisphere is responsible for decoding the non-literal aspects of language, making it possible for us to understand irony and humour, sarcasm and metaphor. Our ability to understand the context of a sentence and to pick up on tone and other non-verbal cues also depends on the right hemisphere. Here, puns click into place, punchlines become funny and the morals of a story are drawn. If this hemisphere is damaged, it is often still possible for those affected to understand formal language when correctly used – but meaning implied in tone, for instance, is lost. Slang, informal or emotional speech becomes incomprehensible. Even the deadest of metaphors becomes unfathomable: it is a nonsense to sit at the foot of a bed or to thread the eye of a needle.
In 1985, Oliver Sacks investigated the response of patients with left-hemisphere and right-hemisphere damage to a speech given by Ronald Reagan. Most of the aphasic patients burst out laughing. Their left hemispheres were damaged; for them, Reagan’s words collapsed in a meaningless heap. What made them laugh? Sacks says that as a way of compensating for their inability to understand words, aphasics are often hypersensitive to non-verbal cues: tone of voice, emphasis, facial expression, gesture and so on. Based on his non-verbal cues – on the way he delivered his speech – Reagan created an amusing impression. On the same ward there was a patient who, like me, had a tumour in her right temporal lobe. Emily D. had been an English teacher and a poet. She had perfect command of formal language, but could no longer grasp the meaning inherent in tone and other non-verbal signs. She didn’t laugh at the president, but she didn’t understand him either. ‘He is not cogent,’ she said. ‘He does not speak good prose. His word use is improper. Either he is brain-damaged, or he has something to conceal.’
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