Why do we dream? And what are nightmares?

Hannah - Thanks, Elisa. So, is there a biological reason for dreaming? We turn to the sleep and dream expert, Dr. Valdas Noreika based at the MRC Cognition and Brain Sciences Unit in Cambridge. He starts by debunking some sleeping myths.

Valdas - You may think that your brain switches off when you sleep, but no. In fact, the regions of your brain that process what we see and feel are just as active when we dream as when we are awake. But instead of using external stimuli such as what we see or hear is brain regions process with things we've learned and remember during the previous days. This means that we dream. But because when we dream we don't consciously choose a single memory to process, different memories can merge together in a spontaneous and rather unsystematic way. This means, we can create whole new worlds and people in our dreams.

Hannah - Thanks, Valdas. So, our dreams are the result of processing memories which can happen chaotically to integrate people, places, and times to create an incoherent dream world. Do we know why these dreams sometimes turn into nightmares though?

Valdas - As well as the memory part of your brain being active during dreaming, the motion processing part is also active including the fear processing limbic system. This might partially explain why negative emotions and feelings are much more common in dreams than in waking life and result in nightmares because what's in our dreams depends on memories of what we experience when we are awake. It's perhaps unsurprising that you've be experiencing high levels of stress in your day to day life, you're more likely to have nightmares. While there is no evidence of universal meaning of different contents of dreams, we certainly have a personal psychological meaning by bringing up traumatic experiences or perhaps by simply reminding us of old friends.