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ABSTRACT: Inhibition plays an essential role in shaping and refining the brain's representation of sensory stimulus attributes. In primary auditory cortex (A1), so-called "sideband" inhibition helps to sharpen the tuning of local neuronal responses. Several distinct types of anatomical circuitry could underlie sideband inhibition, including direct thalamocortical (TC) afferents, as well as indirect intracortical mechanisms. The goal of the present study was to characterize sideband inhibition in A1 and to determine its mechanism by analyzing laminar profiles of neuronal ensemble activity. Our results indicate that both lemniscal and nonlemniscal TC afferents play a role in inhibitory responses via feedforward inhibition and oscillatory phase reset, respectively. We propose that the dynamic modulation of excitability in A1 due to the phase reset of ongoing oscillations may alter the tuning of local neuronal ensembles and can be regarded as a flexible overlay on the more obligatory system of lemniscal feedforward type responses.
Neuron 02/2011; 69(4):805-17. · 14.74 Impact Factor
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ABSTRACT: Attending to a stimulus enhances its neuronal representation, even at the level of primary sensory cortex. Cross-modal modulation can similarly enhance a neuronal representation, and this process can also operate at the primary cortical level. Phase reset of ongoing neuronal oscillatory activity has been shown to be an important element of the underlying modulation of local cortical excitability in both cases. We investigated the influence of attention on oscillatory phase reset in primary auditory and visual cortices of macaques performing an intermodal selective attention task. In addition to responses "driven" by preferred modality stimuli, we noted that both preferred and nonpreferred modality stimuli could "modulate" local cortical excitability by phase reset of ongoing oscillatory activity, and that this effect was linked to their being attended. These findings outline a supramodal mechanism by which attention can control neurophysiological context, thus determining the representation of specific sensory content in primary sensory cortex.
Neuron 11/2009; 64(3):419-30. · 14.74 Impact Factor
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ABSTRACT: Recent anatomical, physiological, and neuroimaging findings indicate multisensory convergence at early, putatively unisensory stages of cortical processing. The objective of this study was to confirm somatosensory-auditory interaction in A1 and to define both its physiological mechanisms and its consequences for auditory information processing. Laminar current source density and multiunit activity sampled during multielectrode penetrations of primary auditory area A1 in awake macaques revealed clear somatosensory-auditory interactions, with a novel mechanism: somatosensory inputs appear to reset the phase of ongoing neuronal oscillations, so that accompanying auditory inputs arrive during an ideal, high-excitability phase, and produce amplified neuronal responses. In contrast, responses to auditory inputs arriving during the opposing low-excitability phase tend to be suppressed. Our findings underscore the instrumental role of neuronal oscillations in cortical operations. The timing and laminar profile of the multisensory interactions in A1 indicate that nonspecific thalamic systems may play a key role in the effect.
Neuron 02/2007; 53(2):279-92. · 14.74 Impact Factor
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ABSTRACT: We examined effects of eye position on auditory cortical responses in macaques. Laminar current-source density (CSD) and multiunit activity (MUA) profiles were sampled with linear array multielectrodes. Eye position significantly modulated auditory-evoked CSD amplitude in 24/29 penetrations (83%), across A1 and belt regions; 4/24 cases also showed significant MUA AM. Eye-position effects occurred mainly in the supragranular laminae and lagged the co-located auditory response by, on average, 38 ms. Effects in A1 and belt regions were indistinguishable in amplitude, laminar profile, and latency. The timing and laminar profile of the eye-position effects suggest that they are not combined with auditory signals at a subcortical stage of the lemniscal auditory pathways and simply "fed-forward" into cortex. Rather, these effects may be conveyed to auditory cortex by feedback projections from parietal or frontal cortices, or alternatively, they may be conveyed by nonclassical feedforward projections through auditory koniocellular (calbindin positive) neurons.
Journal of Neurophysiology 01/2005; 92(6):3522-31. · 3.32 Impact Factor
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ABSTRACT: Recent findings in both monkeys and humans indicate that multisensory convergence occurs in low-level cortical structures generally believed to be unisensory in function. In an in-depth treatment of this theme, this paper reviews anatomical and physiological findings relating to the convergence of visual, somatosensory and auditory signals at early stages of auditory cortical processing. We discuss the potential anatomical sources of the input, and the types of known projections, and attempt to integrate this information with the current hierarchical model of auditory processing. Finally, we consider the functional implications of multisensory integration in early sensory processing.
International Journal of Psychophysiology 11/2003; 50(1-2):5-17. · 2.14 Impact Factor
