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      Hypotheses relating to the function of the claustrum


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          This paper presents a new hypothesis as to the function of the claustrum. Our basic premise is that the claustrum functions as a detector and integrator of synchrony in the axonal trains in its afferent inputs. In the first place an unexpected stimulus sets up a processed signal to the sensory cortex that initiates a focus of synchronized gamma oscillations therein. This focus may then interact with a general alerting signal conveyed from the reticular formation via cholinergic mechanisms, and with other salient activations set up by the stimulus in other sensory pathways that are relayed to the cortex. This activity is relayed from the cortex to the claustrum, which then processes these several inputs by means of multiple competitive intraclaustral synchronized oscillations at different frequencies. Finally it modulates the synchronized outputs that the claustrum distributes to most cortical and many subcortical structures, including the motor cortex. In this way, during multicenter perceptual and cognitive operations, reverberating claustro-cortical loops potentiate weak intracortical synchronizations by means of connected strong intraclaustral synchronizations. These may also occur without a salient stimulus. By this mechanism, the claustrum may play a strong role in the control of interactive processes in different parts of the brain, and in the control of voluntary behavior. These may include the neural correlates of consciousness. We also consider the role of GABAergic mechanisms and deafferentation plasticity.

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          What makes us tick? Functional and neural mechanisms of interval timing.

          Time is a fundamental dimension of life. It is crucial for decisions about quantity, speed of movement and rate of return, as well as for motor control in walking, speech, playing or appreciating music, and participating in sports. Traditionally, the way in which time is perceived, represented and estimated has been explained using a pacemaker-accumulator model that is not only straightforward, but also surprisingly powerful in explaining behavioural and biological data. However, recent advances have challenged this traditional view. It is now proposed that the brain represents time in a distributed manner and tells the time by detecting the coincidental activation of different neural populations.
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            New vistas for alpha-frequency band oscillations.

            The amplitude of alpha-frequency band (8-14 Hz) activity in the human electroencephalogram is suppressed by eye opening, visual stimuli and visual scanning, whereas it is enhanced during internal tasks, such as mental calculation and working memory. alpha-Frequency band oscillations have hence been thought to reflect idling or inhibition of task-irrelevant cortical areas. However, recent data on alpha-amplitude and, in particular, alpha-phase dynamics posit a direct and active role for alpha-frequency band rhythmicity in the mechanisms of attention and consciousness. We propose that simultaneous alpha-, beta- (14-30 Hz) and gamma- (30-70 Hz) frequency band oscillations are required for unified cognitive operations, and hypothesize that cross-frequency phase synchrony between alpha, beta and gamma oscillations coordinates the selection and maintenance of neuronal object representations during working memory, perception and consciousness.
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              High-frequency, long-range coupling between prefrontal and visual cortex during attention.

              Electrical recordings in humans and monkeys show attentional enhancement of evoked responses and gamma synchrony in ventral stream cortical areas. Does this synchrony result from intrinsic activity in visual cortex or from inputs from other structures? Using paired recordings in the frontal eye field (FEF) and area V4, we found that attention to a stimulus in their joint receptive field leads to enhanced oscillatory coupling between the two areas, particularly at gamma frequencies. This coupling appeared to be initiated by FEF and was time-shifted by about 8 to 13 milliseconds across a range of frequencies. Considering the expected conduction and synaptic delays between the areas, this time-shifted coupling at gamma frequencies may optimize the postsynaptic impact of spikes from one area upon the other, improving cross-area communication with attention.

                Author and article information

                Front Integr Neurosci
                Front Integr Neurosci
                Front. Integr. Neurosci.
                Frontiers in Integrative Neuroscience
                Frontiers Media S.A.
                02 August 2012
                : 6
                [1] 1simpleCenter for Brain and Cognition, University of California San Diego, La Jolla CA, USA
                [2] 2simpleMedimark Corporation, Del Mar CA, USA
                Author notes

                Edited by: Warren H. Meck, Duke University, USA

                Reviewed by: Warren H. Meck, Duke University, USA; Antonio Pereira, Federal University of Rio Grande do Norte, Brazil

                *Correspondence: John Smythies, Center for Brain and Cognition, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92039, USA. e-mail: jsmythies@ 123456ucsd.edu
                Copyright © 2012 Smythies, Edelstein and Ramachandran.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.

                Page count
                Figures: 1, Tables: 0, Equations: 0, References: 135, Pages: 16, Words: 15788
                Hypothesis and Theory Article

                binding,claustrum,oscillations,gabaergic interneurons,salience,synchrony,consciousness
                binding, claustrum, oscillations, gabaergic interneurons, salience, synchrony, consciousness


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