Modular Organization of Frequency Integration in Primary Auditory Cortex

University of California, Davis, Davis, California, United States
Annual Review of Neuroscience (Impact Factor: 19.32). 02/2000; 23(1):501-29. DOI: 10.1146/annurev.neuro.23.1.501
Source: PubMed


Two fundamental aspects of frequency analysis shape the functional organization of primary auditory cortex. For one, the decomposition of complex sounds into different frequency components is reflected in the tonotopic organization of auditory cortical fields. Second, recent findings suggest that this decomposition is carried out in parallel for a wide range of frequency resolutions by neurons with frequency receptive fields of different sizes (bandwidths). A systematic representation of the range of frequency resolution and, equivalently, spectral integration shapes the functional organization of the iso-frequency domain. Distinct subregions, or "modules," along the iso-frequency domain can be demonstrated with various measures of spectral integration, including pure-tone tuning curves, noise masking, and electrical cochlear stimulation. This modularity in the representation of spectral integration is expressed by intrinsic cortical connections. This organization has implications for our understanding of psychophysical spectral integration measures such as the critical band and general cortical coding strategies.

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Available from: Christoph E Schreiner
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    • "Much progress has been made in the last several decades in understanding the functions of the mammalian auditory cortex. However, despite our growing knowledge of the anatomical structure (e.g., Kaas et al. 1999; Romanski et al. 1999; Kaas and Hackett 2000; Lee and Winer 2005; Hackett 2011; Winer and Schreiner 2011) and physiological properties (e.g., Merzenich and Brugge 1973; Schreiner and Mendelson 1990; Shamma et al. 1993; Rauschecker et al. 1995; Schreiner et al. 2000; Liang et al. 2001; Ulanovsky et al. 2003; Wang et al. 2005; Bendor and Wang 2005; Schreiner and Winer 2007; Suga et al. 2000) of the auditory cortex, relatively little is known about how neural activity in auditory cortex is linked to auditory perception. Most of what we currently know about auditory cortical processing has come from anesthetized preparations and studies of animals under awake, but passive, conditions. "
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    ABSTRACT: Neural responses in the auditory cortex have historically been measured from either anesthetized or awake but non-behaving animals. A growing body of work has begun to focus instead on recording from auditory cortex of animals actively engaged in behavior tasks. These studies have shown that auditory cortical responses are dependent upon the behavioral state of the animal. The longer ascending subcortical pathway of the auditory system and unique characteristics of auditory processing suggest that such dependencies may have a more profound influence on cortical processing in the auditory system compared to other sensory systems. It is important to understand the nature of these dependencies and their functional implications. In this article, we review the literature on this topic pertaining to cortical processing of sounds.
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    • "Thus, behaviorally important sound frequency information may be further filtered intracortically beyond the TC transformations. Another example of non-homogenous distribution of SRFs is cat A1 (Schreiner et al., 2000; Read et al., 2001; Imaizumi and Schreiner, 2007). Based on multi-unit recordings from cortical layers 3b and 4 in ketamine anesthetized state, broadly-and sharply-tuned neuron clusters based on Q40 values are alternately located dorsoventrally perpendicular to the tonotopic frequency axis. "
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    ABSTRACT: The auditory lemniscal thalamocortical (TC) pathway conveys information from the ventral division of the medial geniculate body to the primary auditory cortex (A1). Although their general topographic organization has been well characterized, functional transformations at the lemniscal TC synapse still remain incompletely codified, largely due to the need for integration of functional anatomical results with the variability observed with various animal models and experimental techniques. In this review, we discuss these issues with classical approaches, such as in vivo extracellular recordings and tracer injections to physiologically identified areas in A1, and then compare these studies with modern approaches, such as in vivo two-photon calcium imaging, in vivo whole-cell recordings, optogenetic methods, and in vitro methods using slice preparations. A surprising finding from a comparison of classical and modern approaches is the similar degree of convergence from thalamic neurons to single A1 neurons and clusters of A1 neurons, although, thalamic convergence to single A1 neurons is more restricted from areas within putative thalamic frequency lamina. These comparisons suggest that frequency convergence from thalamic input to A1 is functionally limited. Finally, we consider synaptic organization of TC projections and future directions for research.
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    • "This neuron’s response was nearly completely suppressed when the S2 tone was placed at 3CF, far away from its CF of 12.25 kHz. We refer to this type of inhibition as “distant inhibition” because it is distinctly different from the sideband inhibition flanking the excitatory region near CF (Schreiner et al., 2000). What makes this distant inhibition interesting and important is that it is often harmonically related to CF. "
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    ABSTRACT: A fundamental structure of sounds encountered in the natural environment is the harmonicity. Harmonicity is an essential component of music found in all cultures. It is also a unique feature of vocal communication sounds such as human speech and animal vocalizations. Harmonics in sounds are produced by a variety of acoustic generators and reflectors in the natural environment, including vocal apparatuses of humans and animal species as well as music instruments of many types. We live in an acoustic world full of harmonicity. Given the widespread existence of the harmonicity in many aspects of the hearing environment, it is natural to expect that it be reflected in the evolution and development of the auditory systems of both humans and animals, in particular the auditory cortex. Recent neuroimaging and neurophysiology experiments have identified regions of non-primary auditory cortex in humans and non-human primates that have selective responses to harmonic pitches. Accumulating evidence has also shown that neurons in many regions of the auditory cortex exhibit characteristic responses to harmonically related frequencies beyond the range of pitch. Together, these findings suggest that a fundamental organizational principle of auditory cortex is based on the harmonicity. Such an organization likely plays an important role in music processing by the brain. It may also form the basis of the preference for particular classes of music and voice sounds.
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