A number of laboratories have been suggesting that top-down vs bottom-up attention signals may be transmitted across the cortex via neural synchronization at beta vs gamma frequencies, respectively (Buschman and Miller, 2007; Bosman et al, 2012; Gregoriou et al, 2009, see review by Wang 2010).  Chanes et al (2013) tested this by entraining the human frontal cortex at those frequencies.  This produced the predicted top-down vs bottom-up effects on behavior: Beta modulated (top-down) response criterion whereas gamma modulated (bottom-up) perceptual sensitivity.  This supports observations that different frequencies of neural synchrony support feedback vs feedforward cortical processing.  It also shows how neural synchrony supports multiplexing of function: Activity from the same neurons has different functional outcomes depending on their rhythmic dynamics.
Chanes et al (2013)

Buschman, T.J. and Miller, E.K. (2007) Top-down versus bottom-up control of attention in the prefrontal and posterior parietal cortices. Science. 315: 1860-1862  The Scientist’s “Hot Paper” for October 2009. View PDF »

G.G. Gregoriou, S.J. Gotts, H. Zhou, R. Desimone (2009) High-frequency, long-range coupling between prefrontal and visual cortex during attention Science, 324 (2009), pp. 1207–1210.

C.A. Bosman, J.-M. Schoffelen, N. Brunet, R. Oostenveld, A.M. Bastos, T. Womelsdorf, B. Rubehn, T. Stieglitz, P. De Weerd, P. Fries (2012) Attentional stimulus selection through selective synchronization between monkey visual areas. Neuron, 75 (2012), pp. 875–888

X.-J. Wang (2010) Neurophysiological and computational principles of cortical rhythms in cognition.  Physiol. Rev., 90 (2010), pp. 1195–1268

About the Author

The Miller Lab uses experimental and theoretical approaches to study the neural basis of the high-level cognitive functions that underlie complex goal-directed behavior. ekmillerlab.mit.edu