ADVERTISEMENT Thanks to a mouse watching clips from 'The Matrix,' scientists have created the largest functional map of a brain to date – a diagram of the wiring connecting 84,000 neurons as they fire off messages. Using a piece of that mouse’s brain about the size of a poppy seed, the researchers identified those neurons and traced how they communicated via branch-like fibres through a surprising 500 million junctions called synapses. The massive dataset, published on Wednesday by the journal