There may be no neat solution to the hard problem yet, but there are one or two practical ways around it. One is to look at "behavioural correlates" or "neurological correlates" of consciousness – in other words, behaviours and neural systems that we suspect are closely related to conscious states. "We can use those as markers of consciousness," says Halina. (This is what Browning and her colleagues at LSE did, using markers such as the presence of nociceptors.)