Non-simple connectivity of the space of light bulbs

Let the space of light bulbs be the space of properly embedded discs in $S^2\times D^2$ that agree with $x_0\times D^2$ near their boundary, with the appropriate topology. Non-simple-connectivity claim. The space of light bulbs is not simply connected. This concerns the topology of the space of embedded discs studied in the four-dimensional light bulb theorem; the statement asserts the existence of a nontrivial loop, although the supplied passage does not provide further details about that loop or its status.