This chapter discusses the peptide chemical code used by the limbic system and suggests that this is the ‘language’ of the brain’s survival machine.

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Excerpts Peptides are remarkably suitable molecules for communication, which is why the body uses them so much for this purpose.  The analogy between a spoken or written language and a chemical code can be over-stretched, but there are some obvious similarities. Let’s return, once more, to language. The English alphabet is made up of 26 letters.  From these letters, an almost infinite number of words is composed.  The number is so large because a word is defined by both the sequence of letters and their number.  There can be words of extremely variable lengths, and some languages use much longer ones than others.  But longer words don’t necessarily contain more information than shorter ones.   The set of words is the vocabulary and their agreed meaning is the semantics of a language.  There are strings of letters that, in English,  are non-words.  Psychologists who study language use them all the time - not to each other (though sometimes one wonders) but as ‘control’ words.  Languages also have a higher order organisation: the order of words, their syntax.  Peptides in the body are made up from an alphabet of 22 amino-acids, like coloured beads on a necklace or letters in a word…….. Peptides are the words of a biological code, and amino-acids are its letters.  As it happens, biochemists have assigned a letter to each of the aminoacids.  Because 22 aminoacids can be arranged in so many ways, and in strings of different lengths, we have an almost infinite chemical vocabulary………. Other tissues use peptides to communicate so they can function properly. Guts squirm, muscles contract, glands secrete, but communication is what the brain does.  Since it’s so good at it, and, indeed, is there to help communication between other organs, we would hardly expect it to need peptides.  These, we might think, are only for those organs that can’t use the computational and communication powers of the brain. The brain, after all, has nerve fibres to communicate and send specific messages.  As with more rational scientific predictions than this, we are in a for a very big surprise. The brain is packed with peptides……….  As you’ll see in the rest of this book,  we are beginning to decode the actions of the peptides in the limbic system, and the story is starting to make sense. As we think about how the brain controls your appetite, your body temperature, your water intake, your sex-life, the way you treat your children, how you cope with stress, we’ll come across peptides, dozens of them. The limbic system responds to peptides to determine what you need. It uses its nerve fibres to deliver peptides to where they are needed, when need arises.   These peptides carry the information both about what you need and what you need to do to survive. Scientific and literary quotes.