Thalamus

Deep in your brain, roughly in the centre of your skull, sit two small, egg-shaped structures of grey matter. They are barely larger than a walnut. And yet they decide, in every waking moment of your life, what you perceive — and what you do not. What becomes conscious — and what remains in the background. Which signals from your body, from your senses, from your surroundings have any chance at all of reaching your consciousness.

These structures are called the thalamus. In medicine they are referred to as the gateway to consciousness. Almost every sensory stimulus — seeing, hearing, tasting, touching, pain, temperature — passes through the thalamus before being processed in the cerebral cortex. Only smell takes a shortcut. Everything else must pass through this gateway.