Lakatos et al have noted that “the role of neuronal oscillations in brain operations has been debated since the discovery of the electroencephalogram.” So this is no small cookie. But the current consensus seems to be that gamma waves with frequencies between 25 and 100 Hz are necessary for sensory processing.
Here’s the theory: Activated groups of neurons have the tendency to oscillate in coherent fashion, affecting the output of the given group and its sensitivity to input. Thus, two groups of neurons will be able to communicate much more effectively if their oscillations are phase-locked. Conversely, neural groups that don’t have this frequency oscillation synchrony will have a much reduced capability to communicate. So, incoming sensory info from the currently attended stimulus will have an advantage during recieving in upstream cortical regions. Also, a “broadcasting center” in the thalamus could distribute the selected rhythm to appropriate cortical regions and prime them to preferentially recieve certain frequencies of sensory input.
The theory implies that the spike-traveling time from sending to recieiving group must be timed correctly and have high fidelity. This is true of afferent thalamocortical axons. Spikes in thalamic neurons arrives in cortical cells in between 1-4 ms and peaks at 2 ms. Indeed, Salami et al (2003) found that the conduction velocity along axons on the thalamocortical tract is 10 times faster than other afferents in mice, due to its selective myelination. So this particular tract must be selected from development to be able to have a low latency interaction with the cortex.
The empirical work I’ve seen backs this theory up. For example, Dockstader et al (2010) used MRI and MEG on healthy participants while administering electrical current stimuli for 0.2 ms just above motor threshold. The participants attended either to the electrical stimuli or a distracting video. Selective attention to the electrical stimuli significantly increased activation in the early phase-locked contralateral primary somatosensory cortex gamma response, starting at 20 ms post-stimuli presentation. This shows that selective attention is likely mediated in neural circuits via gamma oscillations.
Note: Very high oscillations (100-500 Hz) are associated with epilepsy, and those between 250 and 500 Hz are often identified via EEG near the onset of focal seizures. The consensus on the role for lower Hz delta-range oscillations is much less distinct, but it may also be involved in early sensory selection. It is of course possible and likely that there are multiple roles for the gamma waves, and that sensory integration is only one of them.
Inspired by CalTech’s Question #8 for cognitive scientists: “What do you know about high-frequency oscillations (20-50 Hz) in invertebrates or vertebrates? What causes them?”
Salami M, et al. 2003 Change of conduction velocity by regional myelination yields constant latency irrespective of distance between thalamus and cortex. doi: 10.1073/pnas.0937380100 .
Fries P. 2005 A mechanism for cognitive dynamics: neuronal communication through neuronal coherence. doi:10.1016/j.tics.2005.08.011 .
Dockstader C, et al. 2010 Cortical dynamics of selective attention to somatosensory events. doi:10.1016/j.neuroimage.2009.09.035 .
Jirsch JD. 2006 High-frequency oscillations during human focal seizures. doi:10.1093/brain/awl085.