Colgate's own Professor Kelly focuses extensively on gesture and the brain. In a 2010 study entitled "Two sides of the same coin: Speech and gesture mutually interact to enhance comprehension," Kelly and his colleagues proposed the integrated systems hypothesis of gesture and speech.
Speech and Gesture:
1. The interaction is bi-directional, one influences on the other and vice versa
2. The interaction is obligatory, ie we need to use speech and gesture together
The first experiment sought to test the first principle of the hypothesis, that speech and gesture influence one another. Kelly et al.'s results showed that strongly incongruent pairs had significantly more errors compared with weakly incongruent pairs. However, there was not a significant difference in reaction time. Also, there was a main effect for incongruence, but not of target type. These findings suggest that speech comprehension influences gesture comprehension, and vice versa. This also suggests that the influence of each on the other was comparable
The second experiment sought to test the second principle, that this gesture-speech interaction is obligatory. The task was the same as in experiment one, but participants were instructed to pay attention only to the verbal portion of the videos. As it turned out, participants had trouble ignoring the gestures, supporting the connection between speech and gesture. Error rates increased as semantic distance between presented gesture and speech increased.
And, if you're interested, you can find a link to the full journal article here: http://coreservice.mpdl.mpg.de/ir/item/escidoc:68293/components/component/escidoc:295169/content