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Temporal Modulation Transfer Functions in Cat Primary Auditory Cortex: Separating Stimulus Effects From Neural Mechanisms: J Neurophysiol, Vol. 87, No. 1. (1 January 2002), pp. 305-321.Eggerm ont, Jos J. Temporal Modulation Transfer Functions in Cat Primary Auditory Cortex: Separating Stimulus Effects From Neural Mechanisms. J. Neurophysiol. 87: 305-321, 2002. We present here a comparison between the local field potentials (LFP) and multiunit (MU) responses, comprising 401 single units, in primary auditory cortex (AI) of 31 cats to periodic click trains, gamma-tone and time-reversed gamma-tone trains, AM noise, AM tones, and frequency-modu lated (FM) tones. In a large number of cases, the response to all six stimuli was obtained for the same neurons. We investigate whether cortical neurons are likely to respond to all types of repetitive transients and modulated stimuli and whether a dependence on modulating waveform, or tone or noise carrier, exists. In 97% of the recordings, a temporal modulation transfer function (tMTF) for MU activity was obtained for gamma-tone trains, in 92% for periodic click trains, in 83% for time-reversed gamma-tone trains, in 82% for AM noise, in 71% for FM tones, and only in 53% for AM tones. In 31% of the cases, the units responded to all six stimuli in an envelope-follo wing way. These particular units had significantly larger onset responses to each stimulus compared with all other units. The overall response distribution shows the preference of AI units for stimuli with short rise times such as clicks and gamma tones. It also shows a clear asymmetry in the ability to respond to AM noise and AM tones and points to a strong effect of the frequency content of the carrier on the subcortical processing of AM stimuli. Yet all temporal response properties were independent of characteristic frequency and frequency-tuni ng curve bandwidth. We show that the observed differences in the tMTFs for different stimuli are to a large extent produced by the different degree of phase locking of the neuronal firings to the envelope of the first stimulus in the train or first modulation period. A normalization procedure, based on these synchronizatio n differences, unified the tMTFs for all stimuli except clicks and allowed the identification of a largely stimulus-invar iant, low-pass temporal filter function that most likely reflects the properties of synaptic depression and facilitation. For nonclick stimuli, the low-pass filter has a cutoff frequency of ~10 Hz and a slope of ~6 dB/octave. For nonclick stimuli, there was a systematic difference between the vector strength for LFPs and MU activity that can likely be attributed to postactivation suppression mechanisms.

Source: J Neurophysiol, Vol. 87, No. 1. (1 January 2002), pp. 305-321.
Neural processing of amplitude-modu lated sounds.: Physiol Rev, Vol. 84, No. 2. (April 2004), pp. 541-577.Amplit ude modulation (AM) is a temporal feature of most natural acoustic signals. A long psychophysical tradition has shown that AM is important in a variety of perceptual tasks, over a range of time scales. Technical possibilities in stimulus synthesis have reinvigorated this field and brought the modulation dimension back into focus. We address the question whether specialized neural mechanisms exist to extract AM information, and thus whether consideration of the modulation domain is essential in understanding the neural architecture of the auditory system. The available evidence suggests that this is the case. Peripheral neural structures not only transmit envelope information in the form of neural activity synchronized to the modulation waveform but are often tuned so that they only respond over a limited range of modulation frequencies. Ascending the auditory neuraxis, AM tuning persists but increasingly takes the form of tuning in average firing rate, rather than synchronizatio n, to modulation frequency. There is a decrease in the highest modulation frequencies that influence the neural response, either in average rate or synchronizatio n, as one records at higher and higher levels along the neuraxis. In parallel, there is an increasing tolerance of modulation tuning for other stimulus parameters such as sound pressure level, modulation depth, and type of carrier. At several anatomical levels, consideration of modulation response properties assists the prediction of neural responses to complex natural stimuli. Finally, some evidence exists for a topographic ordering of neurons according to modulation tuning. The picture that emerges is that temporal modulations are a critical stimulus attribute that assists us in the detection, discrimination , identification , parsing, and localization of acoustic sources and that this wide-ranging role is reflected in dedicated physiological properties at different anatomical levels.

Source: Physiol Rev, Vol. 84, No. 2. (April 2004), pp. 541-577.
Auditory Discrimination of Amplitude Modulations Based on Metric Distances of Spike Trains: J Neurophysiol, Vol. 97, No. 4. (1 April 2007), pp. 3082-3092.Soun d envelope cues play a crucial role for the recognition and discrimination of communication signals in diverse taxa, such as vertebrates and arthropods. Using a classification based on metric similarities of spike trains we investigate how well amplitude modulations (AMs) of sound signals can be distinguished at three levels of the locust's auditory pathway: receptors and local and ascending neurons. The spike train metric has the advantage of providing information about the necessary evaluation time window and about the optimal temporal resolution of processing, thereby yielding clues to possible coding principles. It further allows one to disentangle the respective contributions of spike count and spike timing to the fidelity of discrimination . These results are compared with the traditional paradigm using modulation transfer functions. Spike trains of receptors and two primary-like local interneurons enable an excellent discrimination of different AM frequencies, up to about 150 Hz. In these neurons discriminabili ty depends almost completely on the timing of spikes, which must be evaluated with a temporal resolution of

Source: J Neurophysiol, Vol. 97, No. 4. (1 April 2007), pp. 3082-3092.
Neural coding strategies in auditory cortex: Hearing Research, Vol. In Press, Corrected ProofIn contrast to the visual system, the auditory system has longer subcortical pathways and more spiking synapses between the peripheral receptors and the cortex. This unique organization reflects the needs of the auditory system to extract behaviorally relevant information from a complex acoustic environment using strategies different from those used by other sensory systems. The neural representation s of acoustic information in auditory cortex can be characterized by three types: (1) isomorphic (faithful) representation s of acoustic structures; (2) non-isomorphic transformation s of acoustic features and (3) transformation s from acoustical to perceptual dimensions. The challenge facing auditory neurophysiolog ists is to understand the nature of the latter two transformation s. In this article, I will review recent studies from our laboratory regarding temporal discharge patterns in auditory cortex of awake marmosets and cortical representation s of time-varying signals. Findings from these studies show that (1) firing patterns of neurons in auditory cortex are dependent on stimulus optimality and context and (2) the auditory cortex forms internal representation s of sounds that are no longer faithful replicas of their acoustic structures.

Source: Hearing Research, Vol. In Press, Corrected Proof
Solar illumination as cause of the equinoctial preference for geomagnetic activity: Geophysical Research Letters, Vol. 28, No. 12. (2001), pp. 2353-2356.

Source: Geophysical Research Letters, Vol. 28, No. 12. (2001), pp. 2353-2356.
Latitudinal effect in semiannual variation of geomagnetic activity: Journal of Geophysical Research, Vol. 108, No. A5. (22 May 2003), 1204.

Source: Journal of Geophysical Research, Vol. 108, No. A5. (22 May 2003), 1204.
Ultraviolet insolation drives seasonal and diurnal space weather variations: Journal of Geophysical Research, Vol. 107, No. A10. (2002), 1305.

Source: Journal of Geophysical Research, Vol. 107, No. A10. (2002), 1305.
The Representation of Amplitude Modulations in the Mammalian Auditory Midbrain: J Neurophysiol, Vol. 100, No. 3. (1 September 2008), pp. 1602-1609.Temp oral modulations in stimulus amplitude are essential for recognizing and categorizing behaviorally relevant acoustic signals such as speech. Despite this behavioral importance, it remains unclear how amplitude modulations (AMs) are represented in the responses of neurons at higher levels of the auditory system. Studies using stimuli with sinusoidal amplitude modulations (SAMs) have shown that the responses of many neurons are strongly tuned to modulation frequency, leading to the hypothesis that AMs are represented by their periodicity in the auditory midbrain. However, AMs in general are defined not only by their modulation frequency, but also by a number of other parameters (duration, duty cycle, etc.), which covary with modulation frequency in SAM stimuli. Thus the relationship between modulation frequency and neural responses as characterized with SAM stimuli alone is ambiguous. In this study, we characterize the representation of AMs in the gerbil inferior colliculus by analyzing neural responses to a series of pulse trains in which duration and interpulse interval are systematically varied to quantify the importance of duration, interpulse interval, duty cycle, and modulation frequency independently. We find that, although modulation frequency is indeed an important parameter for some neurons, the responses of many neurons are also strongly influenced by other AM parameters, typically duration and duty cycle. These results suggest that AMs are represented in the auditory midbrain not only by their periodicity, but by a complex combination of several important parameters. 10.1152/jn.903 74.2008

Source: J Neurophysiol, Vol. 100, No. 3. (1 September 2008), pp. 1602-1609.
Efficient temporal processing of naturalistic sounds.: PLoS ONE, Vol. 3, No. 2. (2008)In this study, we investigate the ability of the mammalian auditory pathway to adapt its strategy for temporal processing under natural stimulus conditions. We derive temporal receptive fields from the responses of neurons in the inferior colliculus to vocalization stimuli with and without additional ambient noise. We find that the onset of ambient noise evokes a change in receptive field dynamics that corresponds to a change from bandpass to lowpass temporal filtering. We show that these changes occur within a few hundred milliseconds of the onset of the noise and are evident across a range of overall stimulus intensities. Using a simple model, we illustrate how these changes in temporal processing exploit differences in the statistical properties of vocalizations and ambient noises to increase the information in the neural response in a manner consistent with the principles of efficient coding.

Source: PLoS ONE, Vol. 3, No. 2. (2008)
The role of overgeneral autobiographic al memory in the development of adult depression following childhood trauma: British Journal of Clinical Psychology, Vol. 43, No. 4., 365.

Source: British Journal of Clinical Psychology, Vol. 43, No. 4., 365.

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