Phase-locked cortical responses to a human speech sound and low-frequency tones in the monkey

Concurrent recordings of average evoked potentials (AEP) and multiple unit activity (MUA) in monkey primary cortex to the syllable /da/, low-frequency tones, and clicks were performed. The AEP in response to the syllable consisted of a periodic alternation superimposed upon slower phasic deflections. All components inverted across the superior temporal plane, indicating their auditory cortical origin. The periodic activity was phase-locked to the syllable's fundamental frequency at a latency of approximately 11 msec. MUA displayed a similar pattern of periodic activity, but with a shorter interval between stimulus and response peaks. This phase-locked MUA occurred only at regions of AEP polarity inversion. Phase-locked activity was also observed in the cortical AEP to 100 and 250 Hz, but not to 500 Hz tonal stimulation. MUA phase-locked to the stimulus frequency only occurred at 100 Hz. Both the periodic and slow components of the AEP were volume-conducted to the dorsal cortical surface. This finding suggests the possibility that similar cortical responses to speech sounds can be recorded from the human scalp.     

Perceiving monetary loss as due to inequity reduces behavioral and cortical responses to pain

Studies indicate that physical and social pain may share some mechanisms and neural correlates. Nothing is known, however, on whether the neural activity in the nociceptive system, as indexed by laser‐evoked potentials (LEPs), is modified when suffering the consequences of a conspecific violating social norms. To explore this issue, we created an interaction scenario where participants could gain money by performing a time‐estimation task. On each win‐trial, another player connected online could arbitrarily decide to keep the participant's pay‐off for him‐ or herself. Thus, participants knew that monetary loss could occur because of their own failure in performing the task or because of the inequitable behavior of another individual. Moreover, participants were asked to play for themselves or on behalf of a third party. In reality, the win/loss events were entirely decided by an ad hoc programmed computer. At the end of the interaction, participants reported if they believed the game‐playing interaction was real. Results showed that the loss due to the opponent's inequitable behavior brought about a reduction both in pain intensity self‐reports and in the amplitude of LEPs' components (i.e. N2, N2/P2, P2a, P2b). Importantly, both the behavioral and neurophysiological effects were found in the participants who believed their deserved payoff was stolen by their opponent. Furthermore, reduction of vertex components was present only when the inequitable behavior was directed toward the self. These results suggest that, far from being a private experience, pain perception might be modulated by the social saliency of interpersonal interactions.     

Effect of auditory cortex lesions on the discrimination of frequency-modulated tones in rats

The lateralization of functions to individual hemispheres of the mammalian brain remains, with the exception of the human brain, unresolved. The aim of this work was to investigate the ability to discriminate between falling and rising frequency-modulated (FM) stimuli in rats with unilateral or bilateral lesions of the auditory cortex (AC). Using an avoidance conditioning procedure, thirsty rats were trained to drink in the presence of a rising FM tone and to stop drinking when a falling FM tone was presented. Rats with a lesion of the AC were able to learn to discriminate between rising and falling FM tones; however, they performed significantly worse than did control rats. A greater deficit in the ability to discriminate the direction of frequency modulation was observed in rats with a right or bilateral AC lesion. The discrimination performance (DP) in these rats was significantly worse than the DP in rats with a left AC lesion. Animals with a right or bilateral AC lesion improved their DP mainly by recognizing the pitch at the beginning of the stimuli. The lesioning of the AC in trained animals caused a significant decrease in DP, down to chance levels. Retraining resulted in a significant increase in DP in rats with a left AC lesion; animals with a right lesion improved only slightly. The results demonstrate a hemispheric asymmetry of the rat AC in the recognition of FM stimuli and indicate the dominance of the right AC in the discrimination of the direction of frequency modulation.     

Event-related desynchronization and synchronization in MEG: Framework for analysis and illustrative datasets related to discrimination of frequency-modulated tones

We introduce a complete framework for the calculation of statistically significant event-related desynchronization and synchronization (ERD/ERS) in the time-frequency plane for magnetoencephalographic (MEG) data, and provide free Internet access to software and illustrative datasets related to a classification task of frequency-modulated (FM) tones. Event-related changes in MEG were analysed on the basis of the normal component of the magnetic field acquired by the 148 magnetometers of the hardware configuration of our whole-head MEG device, and by computing planar gradients in longitudinal and latitudinal direction. Time-frequency energy density for the magnetometer as well as the two gradient configurations is first approximated using short-time Fourier transform. Subsequently, detailed information is obtained from high-resolution time-frequency maps for the most interesting sensors by means of the computationally much more demanding matching pursuit parametrization. We argue that the ERD/ERS maps are easier to interpret in the gradient approaches and discuss the superior resolution of the matching pursuit time-frequency representation compared to short-time Fourier and wavelet transforms. Experimental results are accompanied by the following resources, available from http://brain.fuw.edu.pl/MEG: (a) 48 high-resolution figures presenting the results of four subjects in all applicable settings, (b) raw datasets, and (c) complete software environment, allowing to recompute these figures from the raw datasets.     

Prefrontal theta phase-dependent rTMS-induced plasticity of cortical and behavioral responses in human cortex

BackgroundPrefrontal theta oscillations are involved in neuronal information transfer and retention. Phases along the theta cycle represent varied excitability states, whereby high-excitability states correspond to high-frequency neuronal activity and heightened capacity for plasticity induction, as demonstrated in animal studies. Human studies corroborate this model and suggest a core role of prefrontal theta activity in working memory (WM).Objective/Hypothesis: We aimed at modulating prefrontal neuronal excitability and WM performance in healthy humans, using real-time EEG analysis for triggering repetitive transcranial magnetic stimulation (rTMS) theta-phase synchronized to the left dorsomedial prefrontal cortex.Methods16 subjects underwent 3 different rTMS interventions on separate days, with pulses triggered according to the individual's real-time EEG activity: 400 rTMS gamma-frequency (100 Hz) triplet bursts applied during either the negative peak of the prefrontal theta oscillation, the positive peak, or at random phase. Changes in cortical excitability were assessed with EEG responses following single-pulse TMS, and behavioral effects by using a WM task.ResultsNegative-peak rTMS increased single-pulse TMS-induced prefrontal theta power and theta-gamma phase-amplitude coupling, and decreased WM response time. In contrast, positive-peak rTMS decreased prefrontal theta power, while no changes were observed after random-phase rTMS.ConclusionFindings point to the feasibility of EEG-TMS technology in a theta–gamma phase–amplitude coupling mode for effectively modifying WM networks in human prefrontal cortex, with potential for therapeutic applications.     

Cochlear nucleus unit responses to pure tones in the unanesthetized rabbit

Seventy-six units were studied in the cochlear nucleus of unanesthetized, paralyzed rabbits. Most were located in the dorsal cochlear nucleus. Fifty-eight units were characterized according to their response area by the scheme of Evans and Nelson (1973, Exp. Brain Res., 17, 402–427): 22.5% showed purely excitatory response areas (type ), 72.5% showed mixed excitatory and inhibitory response areas (types III and IV), and 5% showed purely inhibitory response areas (type V). Ten units had virtually no spontaneous activity so were unclassifiable. When characterized according to the scheme of Pfeiffer (1966, Exp. Brain Res., 1, 220–235), 41% of the units were primary-like, 24% were choppers, 20% were pausers, 3% were buildup, and 1% were on units. There was no overall correlation between the two methods of unit classification, but type units showed a high number of chopper patterns. Dorsal cochlear nucleus units in the unanesthetized rabbit showed response characteristics very similar to those which were reported in the decerebrate cat. However, there was a greater prevalence of primary-like, purely excitatory units in the rabbit dorsal cochlear nucleus. This may have reflected a species difference or have been due to technical considerations. It appears that the rabbit cochlear nucleus has very similar physiologic, as well as anatomic, characteristics as does that of the cat.     

Effects of imipramine on the autonomic responses of obsessive-compulsives to auditory tones

It has been argued that a mechanism of clomipramine's efficacy for obsessive-compulsive disorder is its reduction of excessive autonomic reactivity. The present study evaluated this proposed mechanism of action by assessing the effect on autonomic responding of imipramine, which is structurally similar to clomipramine, but lacks therapeutic efficacy for obsessive-compulsives. Twenty-three obsessive-compulsive patients received three sessions of 20 unsignalled 1000-Hz, 100-dB tones of 1-sec duration and 100-msec rise-time. Skin conductance level, response frequency and magnitude, and heart rate were scored for an adaptation period and for each tone onset. Six weeks after the first tone session, during which half of the subjects received imipramine while the remainder received placebo, the second tone assessment was performed. A third tone assessment was performed after an additional 4 weeks of medication. Percentage of nonresponders was also evaluated for each group. Imipramine reduced electrodermal activity and increased heart rate. Skin conductance level and both number and amplitude of responses decreased significantly after 6 weeks of imipramine, compared with placebo, with further attenuation of electrodermal activity after 10 weeks of the drug. Electrodermal nonresponding increased dramatically for the imipramine group as compared to the nondrug group. These results reveal effects of imipramine on autonomic responding, and cast doubt on the hypothesis that a mechanism for successful drug treatment of obsessive-compulsive disorder is decreased autonomic reactivity.     

Dissociating the cortical basis of memory for voices, words and tones

Human speech carries both linguistic content and information about the speaker's identity and affect. While neuroimaging has been used extensively to study verbal memory, there has been little attention to the neural basis of memory for voices. Evidence from studies of aphasia and auditory agnosia suggests that voice memory may rely on anatomically distinct areas in the right temporal and parietal lobes regions, but there is little data on the broader neural systems involved in voice memory. The present study tested the hypothesis that the neural systems involved in voice memory are functionally distinct from the systems involved in word recognition and are primarily located in the right cerebral hemisphere. Subjects performed two-back tasks in which they were required to alternately remember the voices speaking (Voice condition), and the words they produced (Word condition). A tone memory condition was also included, as a non-speech comparison. The contrast between the Voice and Word conditions revealed greater Voice-related effects in left temporal, right frontal and right medial parietal areas, while the Word-related effects appeared in left frontal and bilateral parietal areas. These findings map out a partially right-lateralized fronto-parietal network associated with voice memory, which can be distinguished from predominantly left-hemisphere regions associated with verbal working memory. These results provide further evidence that distinct neural systems are associated with the carrier waves of speech and word identity.     

Mapping responses to frequency sweeps and tones in the inferior colliculus of house mice

In auditory maps of the primary auditory cortex, neural response properties are arranged in a systematic way over the cortical surface. As in the visual system, such maps may play a critical role in the representation of sounds for perception and cognition. By recording from single neurons in the central nucleus of the inferior colliculus (ICC) of the mouse, we present the first evidence for spatial organizations of parameters of frequency sweeps (sweep speed, upward/downward sweep direction) and of whole-field tone response patterns together with a map of frequency tuning curve shape. The maps of sweep speed, tone response patterns and tuning curve shape are concentrically arranged on frequency band laminae of the ICC with the representation of slow speeds, build up response types and sharp tuning mainly in the centre of a lamina, and all (including high) speeds, phasic response types and broad tuning mainly in the periphery. Representation of sweep direction shows preferences for upward sweeps medially and laterally and downward sweeps mainly centrally in the ICC (either striped or concentric map). These maps are compatible with the idea of a gradient of decreasing inhibition from the centre to the periphery of the ICC and by gradients of intrinsic neuronal properties (onset or sustained responding). The maps in the inferior colliculus compare favourably with corresponding maps in the primary auditory cortex, and we show how the maps of sweep speed and direction selectivity of the primary auditory cortex could be derived from the here-found maps of the inferior colliculus.     

Facial and semantic emotional interference: A pilot study on the behavioral and cortical responses to the dual valence association task

Background  

Integration of compatible or incompatible emotional valence and semantic information is an essential aspect of complex social interactions. A modified version of the Implicit Association Test (IAT) called Dual Valence Association Task (DVAT) was designed in order to measure conflict resolution processing from compatibility/incompatibly of semantic and facial valence. The DVAT involves two emotional valence evaluative tasks which elicits two forms of emotional compatible/incompatible associations (facial and semantic).     

Neural and behavioral responses to low-grade inflammation

Neural and behavioral responses after peripheral immune challenge have been observed in numerous studies. The majority of these studies have utilized relatively high doses of lipopolysaccharide (LPS) as the immune stimulant. Little attention has been given to the effects of LPS dose ranges that simulate low grade-inflammation. The current studies were designed to characterize neural and behavioral responses following low-dose LPS stimulation. Results show burrowing and open field activity was significantly impaired following a single i.p. injection of 10, but not 1, μg/kg of LPS. In addition, following repeated 1μg/kg LPS administration for 10 days, animals showed the progressive development of motor deficits over time. To correlate behavior with CNS activity, cFos activation was determined in the paraventricular nucleus, nucleus of the solitary tract, central amygdaloid nucleus, and ventrolateral medulla. Data revealed there was a dose-dependent activation in all brain areas examined, but only the PVN showed significant activation by low-dose LPS. Additionally, animals that received 1μg/kg of LPS for 8 days had PVN cFos activation similar to animals that received a single 10μg/kg LPS injection. These data demonstrate neural and behavior responses can be induced by low-grade inflammation and chronic exposure to sub-threshold levels of LPS can precipitate significantly heightened neural and behavioral responses.     

Reflex and cortical responses to dental stimuli

Tooth pulp stimulation may evoke reflex responses in the orbicularis oculi, temporal, masseter and retronuchal muscles, which may to a varying degree contaminate the cortical evoked responses. The use of repetitive stimulation reduces the amplitude of the cortical responses but avoids the onset of the majority of the muscle reflexes. The appearance of a silent period in the temporal muscle is hard to avoid and it alters the signal recorded from S1 for the first 60–70 msec. In the center-posterior leads, more protected from the EMG signal of the temporal muscle, a first negative deflection is recorded at 43 msec in 60% of subjects.This work was supported by Consiglio Nazionale delle Ricerche, Rome, under grants 79 01841 04 and 81 01830 04     

Acute histopathological responses and long-term behavioral outcomes in mice with graded controlled cortical impact injury

While animal models of controlled cortical impact often display short-term motor dysfunction after injury, histological examinations do not show severe cortical damage. Thus, this model requires further improvement. Mice were subjected to injury at three severities using a Pin-Point~(TM)-controlled cortical impact device to establish secondary brain injury mouse models. Twenty-four hours after injury, hematoxylin-eosin staining, Fluoro-Jade B histofluorescence, and immunohistochemistry were performed for brain slices. Compared to the uninjured side, we observed differences of histopathological findings, neuronal degeneration, and glial cell number in the CA2 and CA3 regions of the hippocampus on the injured side. The Morris water maze task and beam-walking test verified long-term(14–28 days) spatial learning/memory and motor balance. To conclude, the histopathological responses were positively correlated with the degree of damage,as were the long-term behavioral manifestations after controlled cortical impact. All animal procedures were approved by the Institutional Animal Care and Use Committee at Shanghai Jiao Tong University School of Medicine.     

Far-field cochlear microphonic responses to continuous pure tones recorded from the scalps of cats

The cochlear microphonic response to continuous pure tones has been recorded in the 'far field' from the scalps of anesthetized cats. Previous methods for scalp recording used tone pip transients only. Our experiments show that the observed wave forms are not due to electrical or mechanoelectrical artifacts. Neural responses such as brain stem responses or the frequency-following response have been excluded as major contributors to the observed wave forms, which are virtually identical to the round window cochlear microphonic response with respect to (1) wave shape with non-sinusoidal stimuli, (2) intensity-amplitude functions, (3) response phase, and (4) amplitude changes due to superimposed band-limited white noise. The methods of ruling out significant artifacts are applicable to non-invasive recordings from humans.     

Recovery of vibrissae-dependent behavioral responses following barrelfield damage is not dependent upon the remaining somatosensory cortical tissue

Previous work has demonstrated that damage to the primary somatosensory cortex produces substantial deficits in a vibrissal cue-dependent discrimination task which recover gradually over the course of post-injury testing. The present study was designed to evaluate the possible site(s) and mechanisms underlying behavioral recovery in this task. Wistar rats were trained under red light in a T-maze to produce ipsilateral turns depending upon the presence of a vibrissal cue. Animals were then subjected to photothrombotic infractions of either the ipsilateral medial parietal cortex, the ipsilateral primary and secondary somatosensory cortex (SI/SII), the primary and secondary somatosensory cortices of both hemispheres (bilateral SI/SII) or sham surgical procedures. Behavioral testing resumed 24 hours following surgery, and continued for a total of 60 days. The performance of animals with infarcts restricted to the medial parietal cortex did not differ from that of sham-operated controls. Animals with either unilateral or bilateral SI/SII infarcts exhibited a significant decrease in percent correct responding as compared to shams and rats in the medial parietal group. These deficits recovered to pre-infarct levels over approximately 35–40 days. This rate of recovery was slower than the recovery exhibited by animals given medial parietal infarcts which spared the primary barrelfield cortex. The results of this study suggest that neither the contralateral somatosensory cortex nor the vibrissal representation within ipsilateral SII cortex play a critical role in the recovery process. The possibility that subcortical structures underlie the deficits observed following barrelfield cortical damage is discussed.     

Human auditory cortical responses to pitch and to pitch strength

Pitch is a fundamental auditory sensation, underlying both music and speech perception. This study was designed to explore pitch coding in human auditory cortex by testing whether activity in pitch-responsive regions covaries as a function of pitch salience (pitch strength). A psychophysical paradigm was used to confirm three levels of pitch salience for two different pitch-evoking stimuli. The location and magnitude of the response to these stimuli were measured using functional magnetic resonance imaging. A pitch response was found in planum temporale, close to the posterolateral border of Heschl's gyrus. However, the response was not sensitive to pitch salience. One interpretation is that pitch-sensitive regions are maximally responsive to the presence or absence of pitch and not to pitch salience.