Peter Lakatos

Entrainment of Neuronal Oscillations as a Mechanism of Attentional Selection

Whereas gamma-band neuronal oscillations clearly appear integral to visual attention, the role of lower-frequency oscillations is still being debated. Mounting evidence indicates that a key functional property of these oscillations is the rhythmic shifting of excitability in local neuronal ensembles. Here, we show that when attended stimuli are in a rhythmic stream, delta-band oscillations in the primary visual cortex entrain to the rhythm of the stream, resulting in increased response gain for task-relevant events and decreased reaction times. Because of hierarchical cross-frequency coupling, delta phase also determines momentary power in higher-frequency activity. These instrumental functions of low-frequency oscillations support a conceptual framework that integrates numerous earlier findings.

Neuronal Oscillations and Multisensory Interaction in Primary Auditory Cortex

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.

Separation of mismatch negativity and the N1 wave in the auditory cortex of the cat: a topographic study

OBJECTIVE The amplitude distribution of the frequency mismatch negativity (MMN) and that of P1 and N1 components were investigated in cats to reveal their sources in the auditory areas of the neocortex. METHODS Pure tone stimuli were given in a passive oddball paradigm with different degrees of deviance between the standard and deviant tones. Amplitude maps of event-related potential (ERP) components were generated from the responses, recorded in awake, freely moving animals by a chronically implanted epidural electrode matrix, covering both the primary and secondary auditory fields. RESULTS The P1 and N1 components appeared with highest amplitude on the middle ectosylvian gyrus, while the amplitude maximum of the MMN was ventral and rostral to them on the AII area. Both the latency and the peak amplitude of the MMN depended on the degree of deviance. CONCLUSIONS The MMN is generated in the rostroventral part of the secondary auditory area, well separated from the sources of the P1 and N1 components.

Timing of pure tone and noise-evoked responses in macaque auditory cortex.

We compared onset latencies for characteristic frequency pure tone and broadband noise responses in AI and posterior belt regions of the auditory cortex in awake macaques. We found that (1) in AI, responses to characteristic frequency tones and broadband noise have similar latencies, (2) in belt regions, characteristic frequency tone and broadband noise latencies differ significantly; broadband noise latencies are shorter, while characteristic frequency tone latencies are longer than corresponding values in AI, (3) for both pure tone and broadband noise responses in AI, latency decreases with increasing characteristic frequency and (4) despite a similar inverse relationship of tone latency and local characteristic frequency in belt areas, broadband noise latencies are uniformly short, and appear unrelated to local characteristic frequency. Dissociation of broadband noise and pure tone latencies may reflect the use of parallel anatomical routes into belt regions.

Human–simian correspondence in the early cortical processing of multisensory cues

Recent findings in both monkeys and humans indicate that multisensory convergence occurs in low-level cortical structures generally believed to be unisensory in function. There is also evidence that multisensory convergence in higher-order regions occurs at very short post-stimulus latencies. Both types of convergence are of interest as they represent substrates for multisensory interactions in early cortical processing. This paper reviews the correspondence between specific findings in humans and monkeys, focusing on two areas, posterior auditory association cortex and posterior parietal visual association cortex. In each case we examine evidence for “low-level” and/or “early” multisensory convergence in humans, and then examine the results of direct physiological investigation of homologous effects in macaque monkeys. The latter allow a precise physiological and anatomical description of the effects noted in human subjects to be found. We then consider the functional implications of multisensory integration in early and low-level sensory processing, both in relation to our basic hierarchical model of cortical processing and in relation to our understanding of multisensory processes in perception. We end by considering the importance of human–simian homology in the study of the multisensory components of primate (human and monkey) communication.

Effect of deviant probability and interstimulus/interdeviant interval on the auditory N1 and mismatch negativity in the cat auditory cortex

In passive oddball paradigm the effects of changes in interstimulus/interdeviant interval (ISI; IDI) and deviant probability were investigated on mismatch negativity (MMN), auditory N1 wave and the exogenous P1 component of the auditory event-related potential in the cat. An epidural electrode matrix was chronically implanted over the auditory fields of the neocortex, and the amplitudes of the aforementioned components were measured in the location of their amplitude maxima. Dependence of the MMN both on the ISI and IDI as well as deviant probability was revealed, while the amplitude of the P1 and N1 showed dependence merely on the ISI. This method can be used for separation of the two negative, often overlapping components in the cat.