Frontal evoked γ activity modulates behavioural performance in Autism Spectrum Disorders in a perceptual simultaneity task.

Autism spectrum disorders (ASDs) are associated with anomalies in time perception. In a perceptual simultaneity task, individuals with ASD demonstrate superior performance compared to typically developing (TD) controls. γ-activity, a robust marker of visual processing, is reportedly altered in ASD in response to a wide variety of tasks and these differences may be related to superior performance in perceptual simultaneity. Using time-frequency analysis, we assessed evoked γ-band phase-locking in magnetoencephalographic recordings of 16 ASD individuals and 17 age-matched TD controls. Individuals judged whether presented visual stimuli were simultaneous or asynchronous. We identified left frontal γ-activity in ASD, which was associated with a reduced perception of simultaneity. Where feature binding was observed at a neurophysiological level in parieto-occipital cortices in ASD in apparent simultaneity (asynchronous stimuli with short delay between them), this did not predict the correct behavioural outcome. These findings suggest distinct γ profiles in ASD associated with the perception of simultaneity.

Risk of depression enhances auditory Pitch discrimination in the brain as indexed by the mismatch negativity.

OBJECTIVE: Depression is a state of aversion to activity and low mood that affects behaviour, thoughts, feelings and sense of well-being. Moreover, the individual depression trait is associated with altered auditory cortex activation and appraisal of the affective content of sounds. METHODS: Mismatch negativity responses (MMNs) to acoustic feature changes (pitch, timbre, location, intensity, slide and rhythm) inserted in a musical sequence played in major or minor mode were recorded using magnetoencephalography (MEG) in 88 subclinical participants with depression risk. RESULTS: We found correlations between MMNs to slide and pitch and the level of depression risk reported by participants, indicating that higher MMNs correspond to higher risk of depression. Furthermore we found significantly higher MMN amplitudes to mistuned pitches within a major context compared to MMNs to pitch changes in a minor context. CONCLUSIONS: The brains of individuals with depression risk are more responsive to mistuned and fast pitch stimulus changes, even at a pre-attentive level. SIGNIFICANCE: Considering the altered appraisal of affective contents of sounds in depression and the relevance of spectral pitch features for those contents in music and speech, we propose that individuals with subclinical depression risk are more tuned to tracking sudden pitch changes.

Recollection and familiarity make independent contributions to memory judgments.

Recognition memory can be supported by the processes of recollection and familiarity. Recollection is recovery of qualitative information about a prior event. Familiarity is a scalar strength signal that permits judgments of prior occurrence. There is vigorous debate about how these processes are conceptualized, how they contribute to memory judgments, and which brain regions support them. One popular method for investigating these questions is the Remember/Know procedure, where subjects give a Remember response to studied stimuli for which they can recover contextual details of the study encounter, and a Know response when details are not recovered but subjects nevertheless believe that a stimulus was studied. According to one model, Remember responses are strong memories that are typically associated with relatively high levels of recollection and familiarity. Know responses are weaker memories and are typically associated with lower levels of both processes. Data inconsistent with this account were obtained in this experiment, where magnetoencephalographic (MEG) measures of neural activity were acquired in the test phase of a verbal memory task where healthy human volunteers made Remember, Know, or New judgments to studied and unstudied words. An MEG index of the process of recollection was larger for Remember than Know judgments, whereas the reverse was true for a MEG index of familiarity. Critically, this result is predicted by a model where recollection and familiarity make independent contributions to Remember and Know judgments, and provides a powerful constraint when mapping memory processes onto their neural substrates.

A demonstration that task difficulty can confound the interpretation of lateral differences in brain activation between typical and dyslexic readers.

Dyslexic readers (DRs) manifest atypical patterns of brain activity, which may be attributed to aberrant neural connectivity and/or an attempt to activate compensatory pathways. This paper evaluates whether differences in brain activation patterns between DRs and typical readers (TRs) are confounded by task difficulty. Eight DRs and eight TRs matched for age, sex, and nonverbal IQ performed pseudoword rhyming tasks at two levels of difficulty during magnetoencephalography. Task difficulty varied with the number of successive target pseudowords presented before the test pseudoword. Regions of interest were: the temporoparietal area (TPA), the ventral occipital temporal area (VOT), and the inferior frontal gyrus (IFG). Activity was analysed for the 660-ms period after test pseudoword onset. During the discrepant performance condition left hemispheric TPA activation increased across time for TRs, but not DRs, and IFG bihemispheric activation was greater in TRs by the end of the trial. During the equivalent performance condition no group differences in TPA or IFG activation were found. We argue that these results indicate that direct comparison of DR versus TR brain activity is confounded when DRs are more challenged than TRs. This highlights the importance of equating reading group performance during neuroimaging of reading-related tasks.

Eye movements modulate the spatiotemporal dynamics of word processing.

Active reading requires coordination between frequent eye movements (saccades) and short fixations in text. Yet, the impact of saccades on word processing remains unknown, as neuroimaging studies typically employ constant eye fixation. Here we investigate eye-movement effects on word recognition processes in healthy human subjects using anatomically constrained magnetoencephalography, psychophysical measurements, and saccade detection in real time. Word recognition was slower and brain responses were reduced to words presented early versus late after saccades, suggesting an overall transient impairment of word processing after eye movements. Response reductions occurred early in visual cortices and later in language regions, where they colocalized with repetition priming effects. Qualitatively similar effects occurred when words appeared early versus late after background movement that mimicked saccades, suggesting that retinal motion contributes to postsaccadic inhibition. Further, differences in postsaccadic and background-movement effects suggest that central mechanisms also contribute to postsaccadic modulation. Together, these results suggest a complex interplay between visual and central saccadic mechanisms during reading.

Transient and sustained cortical activity elicited by connected speech of varying intelligibility.

BACKGROUND: The robustness of speech perception in the face of acoustic variation is founded on the ability of the auditory system to integrate the acoustic features of speech and to segregate them from background noise. This auditory scene analysis process is facilitated by top-down mechanisms, such as recognition memory for speech content. However, the cortical processes underlying these facilitatory mechanisms remain unclear. The present magnetoencephalography (MEG) study examined how the activity of auditory cortical areas is modulated by acoustic degradation and intelligibility of connected speech. The experimental design allowed for the comparison of cortical activity patterns elicited by acoustically identical stimuli which were perceived as either intelligible or unintelligible. RESULTS: In the experiment, a set of sentences was presented to the subject in distorted, undistorted, and again in distorted form. The intervening exposure to undistorted versions of sentences rendered the initially unintelligible, distorted sentences intelligible, as evidenced by an increase from 30% to 80% in the proportion of sentences reported as intelligible. These perceptual changes were reflected in the activity of the auditory cortex, with the auditory N1m response (~100 ms) being more prominent for the distorted stimuli than for the intact ones. In the time range of auditory P2m response (>200 ms), auditory cortex as well as regions anterior and posterior to this area generated a stronger response to sentences which were intelligible than unintelligible. During the sustained field (>300 ms), stronger activity was elicited by degraded stimuli in auditory cortex and by intelligible sentences in areas posterior to auditory cortex. CONCLUSIONS: The current findings suggest that the auditory system comprises bottom-up and top-down processes which are reflected in transient and sustained brain activity. It appears that analysis of acoustic features occurs during the first 100 ms, and sensitivity to speech intelligibility emerges in auditory cortex and surrounding areas from 200 ms onwards. The two processes are intertwined, with the activity of auditory cortical areas being modulated by top-down processes related to memory traces of speech and supporting speech intelligibility.

Xenomelia: a new right parietal lobe syndrome.

BACKGROUND: Damage to the right parietal lobe has long been associated with various disorders of body image. The authors have recently suggested that an unusual behavioural condition in which otherwise rational individuals desire the amputation of a healthy limb might also arise from right parietal dysfunction. METHODS: Four subjects who desired the amputation of healthy legs (two right, one left and one, at first, bilateral and then left only) were recruited and underwent magnetoencephalography (MEG) scans during tactile stimulation of sites above and below the desired amputation line. Regions of interest (ROIs) in each hemisphere (superior parietal lobule (SPL), inferior parietal lobule, S1, M1, insula, premotor cortex and precuneus) were defined using FreeSurfer software. RESULTS: Analysis of average MEG activity across the 40-140 ms post-stimulation timeframe was carried out using an unpaired t test. This revealed significantly reduced activation only in the right SPL ROI for the subjects' affected legs when compared with both subjects' unaffected legs and that of controls. CONCLUSIONS: The right SPL is a cortical area that appears ideally placed to unify disparate sensory inputs to create a coherent sense of having a body. The authors propose that inadequate activation of the right SPL leads to the unnatural situation in which the sufferers can feel the limb in question being touched without it actually incorporating into their body image, with a resulting desire for amputation. The authors introduce the term 'xenomelia' as a more appropriate name than apotemnophilia or body integrity identity disorder, for what appears to be an unrecognised right parietal lobe syndrome.

Early processing of threat cues in posttraumatic stress disorder-evidence for a cortical vigilance-avoidance reaction.

BACKGROUND: The present study investigated the influence of posttraumatic stress disorder (PTSD) on early visual processing of affective stimuli in survivors of war and torture. METHODS: Trauma-exposed refugees with (n = 36) and without (n = 21) PTSD as well as unexposed control subjects (n = 16) participated in a magnetoencephalography study with pictures that varied in emotional content. RESULTS: We found evidence for a biphasic cortical response in patients with PTSD in comparison with the two control groups. In response to aversive (relative to neutral or positive) pictures, PTSD patients showed elevated cortical activity over right prefrontal areas as early as 130-160 msec after stimulus onset followed by a decrease of the affect-related response in the parieto-occipital cortex at 206-256 msec. CONCLUSIONS: The increased early activity in the right prefrontal cortex most likely represents an enhanced alarm response or the fear network toward aversive stimuli in PTSD, whereas the subsequent decreased activation in right parieto-occipital areas in response to aversive pictures seems to reflect the tendency to disengage from emotional content. This finding is consistent with the hypothesis of a vigilance-avoidance reaction pattern to threat in anxiety disorders and helps to reconcile contradicting results of over- and under-responsiveness in the sensory processing of threatening stimuli in PTSD.

Abnormal neural reactivity to unpredictable sensory events in attention-deficit/hyperactivity disorder.

BACKGROUND: Cortical oscillations in the sensorimotor region in the 8-12-Hz range ("mu rhythms") are associated with basic somatosensory and motor processes as well as top-down processes such as learning, attention, expectancy, and inhibition. Recent studies suggest that reactivity of these rhythms to sensory input reflects a link between perception and action and that abnormalities in this reactivity might reflect impairment in perception-to-action mechanisms. Individuals with attention-deficit/hyperactivity disorder (ADHD) are impaired in tasks requiring sensorimotor function, attention, expectancy, and inhibition, yet their sensorimotor mu responses are unknown. Thus, we investigated mu reactivity in a group of adults with ADHD. METHODS: Sixteen adults with ADHD and 16 matched control subjects received median nerve stimulation in predictable patterns (trains of four stimuli followed by 4-sec gap) or unpredictable patterns (randomly presented trains of two, four, or six stimuli followed by 4-sec gap). With magnetoencephalography, we examined the effects of stimulus patterning (predictable, unpredictable) on mu reactivity to somatosensory stimuli. RESULTS: Compared with control subjects, the ADHD group showed lower mu reactivity overall and no modulation by unpredictable somatosensory input. By contrast, the control group showed robust mu reactivity to stimuli presented in unpredictable but not predictable patterns. These changes were stronger in the contralateral hemisphere compared with the ADHD group. CONCLUSIONS: Cortical mu rhythms are modulated by stimulus predictability and might be involved in attentional alerting (awareness of when an unexpected stimulus occurs). Diminished mu modulation in adult ADHD suggests a possible underlying deficit in the perception-to-action system.

Hemispheric balance in processing attended and non-attended vowels and complex tones.

We compared cortical processing of attended and non-attended vowels and complex tones, using a whole-head neuromagnetometer, to test for possible hemispheric differences. Stimuli included vowels [a] and [i], spoken by two female Finnish speakers, and two complex tones, each with two pure tone components corresponding to the first and second formant frequencies (F1-F2) of the vowels spoken by speaker 1. Sequences including both vowels and complex tones were presented to eight Finnish males during passive and active (phoneme/speaker/complex tone identification) listening. Sequences including only vowels were presented to five of the subjects during passive listening and during a phoneme identification task. The vowel [i] spoken by speaker 1 and the corresponding complex tone were frequent, non-target stimuli. Responses evoked by these frequent stimuli were analyzed. Cortical activation at approximately 100 ms was stronger for the complex tone than the vowel in the right hemisphere (RH). Responses were similar during active and passive listening. Hemispheric balance remained the same when the vowel was presented in sequences including only vowels. The reduction of RH activation for vowels as compared with complex tones indicates a relative increase of left hemisphere involvement, possibly reflecting a shift towards more language-specific processing.

Hearing the sound of silence: a magnetoencephalographic study.

We visualized the brain activity for retrieval imagery of a sound using dual 37-channel magnetometers in seven right-handed healthy subjects. A soundless video image of a hammer striking an anvil was presented on a screen. Significantly larger evoked magnetic fields were recorded, dominantly in the right hemisphere, in six subjects when they imagined the sound than when they did not. The initial peak of the response was 151.0 +/- 26.5 ms (mean +/- s.d.) after the blow. Equivalent current dipoles (ECDs) for the responses recorded from the right hemisphere were located around the inferior frontal sulcus in three subjects and in the insular region in three subjects, but reliable ECDs were not estimated from the left hemisphere. The results suggested that the initial activity for sound retrieval imagery appeared around the inferior frontal and insular areas, dominantly in the right hemisphere.

Temporal window of integration of auditory information in the human brain.

A deviation in the acoustic environment activates an automatic change-detection system based on a memory mechanism that builds a neural trace representing the preceding sounds. The present study revealed that the auditory-cortex mechanisms underlying this sensory memory integrate acoustic events over time, producing a perception of a unitary auditory event. We recorded magnetic responses (MMNm) to occasional stimulus omissions in trains of stimuli presented at a constant stimulus-onset asynchrony (SOA) that was, in different blocks, either shorter or longer in duration than the assumed length of the temporal window of integration. A definite MMNm was elicited by stimulus omission only with the three shortest SOAs used: 100, 125, and 150 ms, but not with 175 ms. Thus, 160-170 ms was estimated as the length of the temporal window used by the central auditory system in integrating successive auditory input into auditory event percepts.