Recent studies shed light on how the brain processes temporally distributed information
The vast majority of cognitive neuroscience research has focused on mapping brain responses to static stimuli during highly simplified experimental paradigms, and indeed such studies have provided valuable information about the hierarchical processing steps that take place in the human brain, with sensory cortical areas processing relatively simple stimulus features and higher-order association cortical areas processing more complex aspects of perceptual objects. This is, however, only half of the story, as stimuli and events in the real world almost always take place in a temporal context. For example, the meaning of a single word is greatly shaped by the preceding words, gestures, and social interactions. Thus, the brain needs to have mechanisms that accumulate information over longer timescales in order to make sense of things that are unfolding across time.
Two distinct studies in the most recent issue of the prestigious journal Neuron have addressed the issue of where in the brain processing of temporally distributed information takes place using very interesting experimental setups. In the first study, Yaron et al. (2012) presented anesthetized rats with auditory stimulation that either contained periodicity or was completely random. The authors hypothesized that if auditory cortical neurons code periodicity information the responses to sounds presented in the periodicity-containing sequences should be smaller than responses to sounds when they are presented randomly. Indeed, their results showed this to be the case and the authors conclude that neurons in the auditory cortex are sensitive to the detailed structure of sound sequences over timescales even as long as minutes. In the second study, Honey et al. (2012) measured electrocorticography in human subjects during watching of intact and temporally scrambled movies. By inspecting the degree of synchrony of neuronal activity across cortical locations in the intact vs. scrambled movie conditions, the authors noted that while sensory cortical areas synchronized over very short times scales, within higher-order regions slow power fluctuations were more reliable for the intact than the scrambled movie, suggesting that these regions accumulate information over longer time periods.
These studies provide recent examples of a highly exciting and relatively new area of research that is focusing on how the brain is able to accumulate information over longer time scales to make sense of words, sentences, melodies, and patterns of social interactions. The finding that auditory cortex of rats can track periodicity over timescales of minutes is truly significant and is bound to inspire further research; on the other hand, the experimental setup of using scrambled vs. intact movies to investigate temporal receptive windows in humans based on recording of brain electrical activity provide a significant methodological step forward for further research in humans.
Honey CJ, Thesen T, Donner TH, Silbert LJ, Carlson CE, Devinsky O, Doyle WK, Rubin N, Heeger DJ, Hasson U. Slow cortical dynamics and the accumulation of information over long timescales. Neuron (2012) 76: 423–434. http://dx.doi.org/10.1016/j.neuron.2012.08.011
Yaron A, Hershenhoren I, Nelken I. Sensitivity to complex statistical regularities in rat auditory cortex. Neuron (2012) 76: 603-615. http://dx.doi.org/10.1016/j.neuron.2012.08.025