Nelken, I. Processing of complex stimuli and natural scenes in the auditory cortex. Curr. Opin. Neurobiol. 14, 474-480

Department of Neurobiology, The Silberman Institute of Life Sciences, and the Interdisciplinary Center for Neural Computations, Givat Ram 91904, Jerusalem, Israel.
Current Opinion in Neurobiology (Impact Factor: 6.63). 09/2004; 14(4):474-80. DOI: 10.1016/j.conb.2004.06.005
Source: PubMed


Neuronal responses in auditory cortex show a fascinating mixture of characteristics that span the range from almost perfect copies of physical aspects of the stimuli to extremely complex context-dependent responses. Fast, highly stimulus-specific adaptation and slower plastic mechanisms work together to constantly adjust neuronal response properties to the statistics of the auditory scene. Evidence with converging implications suggests that the neuronal activity in primary auditory cortex represents sounds in terms of auditory objects rather than in terms of invariant acoustic features.

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    • "In other words, the neuron's previous experience determines its future sensitivity, which suggests SSA may be a basic mechanism underlying predictive coding (Friston, 2005; Baldeweg, 2006; Bar, 2007; Winkler et al., 2009; Bendixen et al., 2012). Moreover, previous studies have also suggested that SSA could be linked to auditory memory, recognition of acoustic objects and auditory scene analysis (Nelken, 2004; Winkler et al., 2009). "
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    ABSTRACT: To follow an ever-changing auditory scene, the auditory brain is continuously creating a representation of the past to form expectations about the future. Unexpected events will produce an error in the predictions that should "trigger" the network's response. Indeed, neurons in the auditory midbrain, thalamus and cortex, respond to rarely occurring sounds while adapting to frequently repeated ones, i.e., they exhibit stimulus specific adaptation (SSA). SSA cannot be explained solely by intrinsic membrane properties, but likely involves the participation of the network. Thus, SSA is envisaged as a high order form of adaptation that requires the influence of cortical areas. However, present research supports the hypothesis that SSA, at least in its simplest form (i.e., to frequency deviants), can be transmitted in a bottom-up manner through the auditory pathway. Here, we briefly review the underlying neuroanatomy of the corticofugal projections before discussing state of the art studies which demonstrate that SSA present in the medial geniculate body (MGB) and inferior colliculus (IC) is not inherited from the cortex but can be modulated by the cortex via the corticofugal pathways. By modulating the gain of neurons in the thalamus and midbrain, the auditory cortex (AC) would refine SSA subcortically, preventing irrelevant information from reaching the cortex.
    Frontiers in Systems Neuroscience 03/2015; 9:19. DOI:10.3389/fnsys.2015.00019
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    • "In contrast to the above view and in concordance with previous computational studies (Buonomano & Merzenich, 1995; May & Tiitinen , 2007, 2010; Buonomano & Maass, 2009), the current results demonstrate that synaptic adaptation might have an unexpected function in contributing to temporal integration of auditory information – possibly the central function of auditory cortex (Nelken, 2004) – by allowing for individual cortical neurons to respond selectively to the temporal structure of stimuli. A counterintuitive consequence of this is that activity-dependent depression of excitatory synapses between pyramidal cell populations not only leads to forward suppression in the case of masker–tone interactions, but could also underlie response facilitation reflecting temporal selectivity (see also Goudar & Buonomano, 2014). "
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    ABSTRACT: Incoming sounds are represented in the context of preceding events, and this requires a memory mechanism that integrates information over time. Here, it was demonstrated that response adaptation, the suppression of neural responses due to stimulus repetition, might reflect a computational solution that auditory cortex uses for temporal integration. Adaptation is observed in single-unit measurements as two-tone forward masking effects and as stimulus-specific adaptation (SSA). In non-invasive observations, the amplitude of the auditory N1m response adapts strongly with stimulus repetition, and it is followed by response recovery (the so-called mismatch response) to rare deviant events. The current computational simulations described the serial core-belt-parabelt structure of auditory cortex, and included synaptic adaptation, the short-term, activity-dependent depression of excitatory corticocortical connections. It was found that synaptic adaptation is sufficient for columns to respond selectively to tone pairs and complex tone sequences. These responses were defined as combination sensitive, thus reflecting temporal integration, when a strong response to a stimulus sequence was coupled with weaker responses both to the time-reversed sequence and to the isolated sequence elements. The temporal complexity of the stimulus seemed to be reflected in the proportion of combination-sensitive columns across the different regions of the model. Our results suggest that while synaptic adaptation produces facilitation and suppression effects, including SSA and the modulation of the N1m response, its functional significance may actually be in its contribution to temporal integration. This integration seems to benefit from the serial structure of auditory cortex. © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.
    European Journal of Neuroscience 03/2015; 41(5):615-30. DOI:10.1111/ejn.12820 · 3.18 Impact Factor
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    • "Moreover , these data further argue against the notion that the neural organization of the auditory scene starts at a cortical level (cf. Nelken, 2004). Harmonic pitch sieve analyses demonstrated that in both AN and brainstem representations, the degree of neural harmonicity was related to stimulus mistuning; high neural harmonicity was related to tuned stimuli that promote single auditory object perception while low harmonicity was related to mistuned stimuli, which listeners hear as multiple objects. "
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    ABSTRACT: Natural soundscapes often contain multiple sound sources at any given time. Numerous studies have reported that in human observers, the perception and identification of concurrent sounds is paralleled by specific changes in cortical event-related potentials (ERPs). Although these studies provide a window into the cerebral mechanisms governing sound segregation, little is known about the subcortical neural architecture and hierarchy of neurocomputations that lead to this robust perceptual process. Using computational modeling, scalp-recorded brainstem/cortical ERPs, and human psychophysics, we demonstrate that a primary cue for sound segregation, i.e., harmonicity, is encoded at the auditory nerve level within tens of milliseconds after the onset of sound and is maintained, largely untransformed, in phase-locked activity of the rostral brainstem. As then indexed by auditory cortical responses, (in)harmonicity is coded in the signature and magnitude of the cortical object-related negativity (ORN) response (150-200ms). The salience of the resulting percept is then captured in a discrete, categorical-like coding scheme by a late negativity response (N5; ~500ms latency), just prior to the elicitation of a behavioral judgment. Subcortical activity correlated with cortical evoked responses such that weaker phase-locked brainstem responses (lower neural harmonicity) generated larger ORN amplitude, reflecting the cortical registration of multiple sound objects. Studying multiple brain indices simultaneously helps illuminate the mechanisms and time-course of neural processing underlying concurrent sound segregation and may lead to further development and refinement of physiologically driven models of auditory scene analysis. Copyright © 2014. Published by Elsevier Ltd.
    Neuropsychologia 12/2014; 68. DOI:10.1016/j.neuropsychologia.2014.12.020 · 3.30 Impact Factor
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