Catching the Switch using fMRI.  click here to download Powerpoint presentation.

The switch occurs every few seconds, much faster than the haemodynamic response that the usual basis of fMRI, so it is difficult to catch.

In this movie, spatial resolution has been sacrificed so that an image can taken every second while a subject experiences rivalry.

The coronal slice is at the level of the midbrain-diencephalic junction. Large blood vessels at the base of the skull give a distracting signal there, but one can orient using the callosum and lateral ventricles which are just visible in this raw scan.

Notice that there is a region of the midbrain, just to the left of midline, which flashes every few seconds, in synchrony with rivalry switches. This was dubbed the "lighthouse" because of its unusual signal intensity. A partner "lighthouse" is justvisible in anti-phase in some frames.