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Electronic Letters to:
- BehavioralSystemsCognitive:
Lucia Melloni, Carlos Molina, Marcela Pena, David Torres, Wolf Singer, and Eugenio Rodriguez- Synchronization of Neural Activity across Cortical Areas Correlates with Conscious Perception
J. Neurosci. 2007; 27: 2858-2865[Abstract] [Full text] [PDF]
eLetters: Submit a response to this article
Electronic letters published:
Stimulus-related synchronization,'visual binding' and signal-to-noise ratio in the brain.
- walter g. sannita (3 April 2007)
Stimulus-related synchronization,'visual binding' and signal-to-noise ratio in the brain. 3 April 2007 
walter g. sannita,
professor of neurology
dept. of motor science, university of genova, 16132 genova, italySend letter to journal:
Re: Stimulus-related synchronization,'visual binding' and signal-to-noise ratio in the brain.
wgs{at}dism.unige.it walter g. sannita
Stimulus-related synchronization,'visual binding' and signal-to-noise ratio in the brain.
Walter G. Sannita
Department of Motor Science, University of Genova, Genova, Italy, and Department of Psychiatry, State University of New York, Stony Brook, NY, USA
Our visual system translates the external world into images and we recognize and categorize objects. Usually referred to as 'visual binding', the integration of visual features into coherent, three-dimensional perceptual representations - an illusion forever builds into the brain through experience – is a classic problem (“the binding problem”) and a matter of debate [1]. Transient increase in the phase synchrony across cortical areas is the critical process Melloni et al. suggest mediate in the access to conscious perception [2]. This adds to the hypothesis that synchronization and attentional selection are necessary for cortical integration to occur and mediate in 'visual binding' [1]. Critics of the bottom-up hypothesis argue that selective synchronization appears unlikely based on neural computation and that whatever visual binding may be, it seems unaffected when the primary visual areas are damaged. Some top-down organization from non-primarily visual cortices is suggested, consistent with the massive involvement of the primate brain in vision [1]. Observations from a neuromagnetic experiment on human vision [3] add to the controversy. Meaningful words embedded in white dynamical noise were presented with a stimulus signal-to-noise function across noise levels that matched the "threshold-stochastic resonance" paradigm (threshold-SR) [4]. As predicted, word recognition depended on the signal/noise interaction; activation in primary cortex fitted the stimulus signal-to- noise function. Unexpectedly, however, brain activation matched the stimulus signal-to-noise function also in non-primary visual cortices and at temporal-central brain sites where language processing is thought to occur irrespective of the physical properties of visual input [3]. No direct inference about visual binding is obviously possible based on this observation. Yet, this transfer of the signal-to-noise function from visual input to visual cortex to language areas is consistent with the hypothetized bottom-up information processing [1]; implications in lower- level brain function are also conceivable and would suggest some compatibility with or intrinsic adaptation of brain processes to, the threshold-SR function. Object recognition is likely to occur because ‘we already have in the brain a model of that object and this model is activated through vision' [4]. Some internal model fitting the signal-to- noise function of the threshold-SR stimulus applied in this study therefore does not appear implausible and would be in the line of evidence that interaction between neuronal signalling and noise is ubiquitous in the brain [5].
1.Neuron. 1999; 24, 7-127 (special review on visual binding). 2. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. Synchronization of neural activity across cortical areas correlates with conscious perception. J Neurosci. 2007;27:2858-2865. 3. Sorrentino A, Parkkonen L, Piana M, Massone AM, Narici L, Carozzo S, Riani M, Sannita WG. Modulation of brain and behavioural responses to cognitive visual stimuli with varying signal-to-noise ratios. Clin Neurophysiol. 2006; 117: 1098-1105. 4. Wiesenfeld, K. and Moss, F. Stochastic resonance and the benefits of noise: from ice ages to crayfish and SQUIDs. Nature 1995; 373: 33-36; Gammaitoni L, Hanggi P, Jung P, Marchesoni F. Stochastic Resonance. Rev Mod Phys 1998; 70:223 – 288; Moss F, Ward L, Sannita WG. Stochastic resonance and sensory information processing: a tutorial and review of application. Clin Neurophysiol, 115 : 267-281, 2004. 5. Ito M. Internal model visualized. Nature 2000; 403, 153-154
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