Language
While it is difficult to compare the brains and thought processes of different animals, how they communicate among themselves is more open to study. One thing that separates us most significantly from other species is our use of a complex verbal and written language.
Many animals are known to communicate with one another using sound, but none has developed a system as complex as human language. It encompasses features such as semantics (meaning is attached to sounds/words) and syntax (the order and arrangement of sounds/words is important).
Allowing communication and coordination of activities, and the capture of knowledge to be passed on, it has probably been fundamental to our success. What do we know of how the brain manages language?
Influential writer and thinker Noam Chomsky said: "When we study human language, we are approaching what some might call the 'human essence', the distinctive qualities of mind that are, so far as we know, unique to man." (Noam Chomsky, 'Language and Mind'.)
Chomsky developed the idea of an 'innate grammar' – that all infants are born with an ability to develop language. Which language they learn depends on where they are born. Recent research suggests that language skills are indeed programmed into our genes and our brain's wiring.
For example, by studying a family with a specific language disorder, a group at Oxford discovered a gene associated with language ability – FOXP2. The gene seems to be involved in the development of the brain. When children inherit a mutation in FOXP2, their brains do not wire together properly and they struggle to communicate verbally, even though most other aspects of brain function are normal. Remarkably, human FOXP2 is only slightly different from the chimp version. Although it is not the only gene enabling language to develop, it seems to have been important in human evolution.
Other areas of the brain are specialised for particular tasks associated with language. Broca's area, for example, is important for speech. In 1861, French neuroscientist Paul Broca described a patient who had almost completely lost the ability to speak – he could only say 'tan' (which became his nickname). When Tan died, Broca carried out a post-mortem and identified damage in an area of the cerebral cortex – which was later named Broca's area in his honour.
Later that century Karl Wernicke found that damage to a nearby area removed the ability to understand language rather than speak it. Because patients could not understand what they were saying, patients also tended to speak nonsense (sometimes described as 'word salad'). He got his name immortalised too, in Wernicke's area.
A huge variety of language impairments are now known to exist – collectively known as aphasia. The nature of the impairment depends on the precise area of the brain affected. Some forms of aphasia are remarkably restricted. Patients may be able to describe but not name objects, or particular classes of objects such as tools or animals. Others may have difficulties just with verbs. Others can tell the differences between colours but cannot name them.
If the links between vision and language processing centres are disrupted, a patient may be able to hear and understand as normal but cannot read. Strikingly, they can write fluently but cannot understand what they have written.
Although obviously difficult for patients, the extraordinary diversity of language disorders does at least provide researchers with an opportunity to find out more about the links between brain structure and activity and specific language deficits.