The internal representation of vowel spectra investigated using behavioral response-triggered averaging

Listeners presented with noise were asked to press a key 13 whenever they heard the vowels [a] or [i:]. The noise had a random spectrum, with levels in 60 frequency bins changing every 0.5 s. Reverse correlation was used to average the spectrum of the noise prior to each key press, thus estimating the features of the vowels for which the participants were listening. The formant frequencies of these reverse-correlated vowels were similar to those of their respective whispered vowels. The success of this response-triggered technique suggests that it may prove useful for estimating other internal representations, including perceptual phenomena like tinnitus

Conceptual coordination bridges information processing and neurophysiology

Information processing theories of memory and skills can be reformulated in terms of how categories are physically and temporally related, a process called conceptual coordination. Dreaming can then be understood as a story understanding process in which two mechanisms found in everyday comprehension are missing: conceiving sequences (chunking categories in time as a higher-order categorization) and coordinating across modalities (e.g., relating the sound of a word and the image of its meaning). On this basis, we can readily identify isomorphisms between dream phenomenology and neurophysiology, and explain the function of dreaming as facilitating future coordination of sequential, cross-modal categorization (i.e., REM sleep lowers activation thresholds, “unlearning”)

Stimulus-invariant processing and spectrotemporal reverse correlation in primary auditory cortex

The spectrotemporal receptive field (STRF) provides a versatile and integrated, spectral and temporal, functional characterization of single cells in primary auditory cortex (AI). In this paper, we explore the origin of, and relationship between, different ways of measuring and analyzing an STRF. We demonstrate that STRFs measured using a spectrotemporally diverse array of broadband stimuli -- such as dynamic ripples, spectrotemporally white noise, and temporally orthogonal ripple combinations (TORCs) -- are very similar, confirming earlier findings that the STRF is a robust linear descriptor of the cell. We also present a new deterministic analysis framework that employs the Fourier series to describe the spectrotemporal modulations contained in the stimuli and responses. Additional insights into the STRF measurements, including the nature and interpretation of measurement errors, is presented using the Fourier transform, coupled to singular-value decomposition (SVD), and variability analyses including bootstrap. The results promote the utility of the STRF as a core functional descriptor of neurons in AI.Comment: 42 pages, 8 Figures; to appear in Journal of Computational Neuroscienc

A new method to detect event-related potentials based on Pearson\u2019s correlation

Event-related potentials (ERPs) are widely used in brain-computer interface applications and in neuroscience. Normal EEG activity is rich in background noise, and therefore, in order to detect ERPs, it is usually necessary to take the average from multiple trials to reduce the effects of this noise. The noise produced by EEG activity itself is not correlated with the ERP waveform and so, by calculating the average, the noise is decreased by a factor inversely proportional to the square root of N, where N is the number of averaged epochs. This is the easiest strategy currently used to detect ERPs, which is based on calculating the average of all ERP\u2019s waveform, these waveforms being time- and phase-locked. In this paper, a new method called GW6 is proposed, which calculates the ERP using a mathematical method based only on Pearson\u2019s correlation. The result is a graph with the same time resolution as the classical ERP and which shows only positive peaks representing the increase\u2014in consonance with the stimuli\u2014in EEG signal correlation over all channels. This new method is also useful for selectively identifying and highlighting some hidden components of the ERP response that are not phase-locked, and that are usually hidden in the standard and simple method based on the averaging of all the epochs. These hidden components seem to be caused by variations (between each successive stimulus) of the ERP\u2019s inherent phase latency period (jitter), although the same stimulus across all EEG channels produces a reasonably constant phase. For this reason, this new method could be very helpful to investigate these hidden components of the ERP response and to develop applications for scientific and medical purposes. Moreover, this new method is more resistant to EEG artifacts than the standard calculations of the average and could be very useful in research and neurology. The method we are proposing can be directly used in the form of a process written in the well-known Matlab programming language and can be easily and quickly written in any other software language

Molecular Requirements for Ethanol Differential Allosteric Modulation of Ligand-Gated Ion Channels Based on Selective G Beta Gamma Modulation

It is now believed that the allosteric modulation produced by ethanol in glycine receptors (GlyRs) depends on alcohol binding to discrete sites within the protein structure. Thus, the differential ethanol sensitivity of diverse GlyR isoforms and mutants was explained by the presence of specific residues in putative alcohol pockets. Here, we demonstrate that ethanol sensitivity in two LGIC members, the GlyR adult alpha1 and embryonic alpha2 subunits, can be modified through selective mutations that rescued or impaired Gbetagamma modulation. Even though that both isoforms were able to physically interact with Gbetagamma, only the alpha1 GlyR was functionally modulated by Gbetagamma and pharmacological ethanol concentrations. Remarkably, the simultaneous switching of two transmembrane and a single extracellular residue in alpha2 GlyRs was enough to generate GlyRs modulated by Gbetagamma and low ethanol concentrations. Interestingly, while we found that these TM residues were different to those in the alcohol binding site, the extracellular residue was recently implicated in conformational changes important to generate a pre-open activated state that precedes ion channel gating. Thus, these results support the idea that the differential ethanol sensitivity of these two GlyR isoforms rests on conformational changes in transmembrane and extracellular residues within the ion channel structure rather than in differences in alcohol binding pockets. Our results describe the molecular basis for the differential ethanol sensitivity of two LGIC members based on selective Gbetagamma modulation and provide a new mechanistic framework for allosteric modulations of abuse drugs

High frequency repetitive transcranial magnetic stimulation to the left dorsolateral prefrontal cortex modulates sensorimotor cortex function in the transition to sustained muscle pain

Based on reciprocal connections between the dorsolateral prefrontal cortex (DLPFC) and basal-ganglia regions associated with sensorimotor cortical excitability, it was hypothesized that repetitive transcranial magnetic stimulation (rTMS) of the left DLPFC would modulate sensorimotor cortical excitability induced by muscle pain. Muscle pain was provoked by injections of nerve growth factor (end of Day-0 and Day-2) into the right extensor carpi radialis brevis (ECRB) muscle in two groups of 15 healthy participants receiving 5 daily sessions (Day-0 to Day-4) of active or sham rTMS. Muscle pain scores and pressure pain thresholds (PPTs) were collected (Day-0, Day-3, Day-5). Assessment of motor cortical excitability using TMS (mapping cortical ECRB muscle representation) and somatosensory evoked potentials (SEPs) from electrical stimulation of the right radial nerve were recorded at Day-0 and Day-5. At Day-0 versus Day-5, the sham compared to active group showed: Higher muscle pain scores and reduced PPTs (P < 0.04); decreased frontal N30 SEP (P < 0.01); increased TMS map volume (P < 0.03). These results indicate that muscle pain exerts modulatory effects on the sensorimotor cortical excitability and left DLPFC rTMS has analgesic effects and modulates pain-induced sensorimotor cortical adaptations. These findings suggest an important role of prefrontal to basal-ganglia function in sensorimotor cortical excitability and pain processing

The effect of transcranial direct current stimulation on perception of effort in an isolated isometric elbow flexion task

This is the author's manuscript as accepted for publication in Motor Control. The final published article is available from the link below, copyright @ 2013 Human Kinetics.The purported ergogenic actions of transcranial direct current stimulation (tDCS) applied to motor cortex (M1) on force production and perception of effort were investigated using a 10-item numerical rating scale (0–10 NRS) in nonfatiguing bouts of a force-matching task utilizing isometric elbow flexion. Using a crossover design, 12 healthy volunteers received sham, anodal, and cathodal tDCS randomly for 10 min (1.5 mA, 62 ìA/cm2) to the left M1 in a double-blind manner. Cor- ticospinal excitability changes were also monitored using transcranial magnetic stimulation (TMS) with surface electromyography (sEMG) to monitor both motor evoked potentials (MEPs) and force-EMG from right m. biceps brachii and m. brachioradialis brachii. No significant differences between the verum and sham stimulation were obtained for elbow flexion maximum voluntary force, perception of effort, or sEMG. There were also no significant differences in MEP changes for the types of tDCS, which is consistent with reports that tDCS excitability effects are diminished during ongoing cognitive and motor activities.Brunel Universit