Age-related alteration in processing of temporal sound features in the auditory midbrain of the CBA mouse

The perception of complex sounds, such as speech and animal vocalizations, requires the central auditory system to analyze rapid, ongoing fluctuations in sound frequency and intensity. A decline in temporal acuity has been identified as one component of age-related hearing loss. The detection of short, silent gaps is thought to reflect an important fundamental dimension of temporal resolution. In this study we compared the neural response elicited by silent gaps imbedded in noise of single neurons in the inferior colliculus (IC) of young and old CBA mice. IC neurons were classified by their temporal discharge patterns. Phasic units, which accounted for the majority of response types encountered, tended to have the shortest minimal gap thresholds (MGTs), regardless of age. We report three age-related changes in neural processing of silent gaps. First, although the shortest MGTs (1-2 msec) were observed in phasic units from both young and old animals, the number of neurons exhibiting the shortest MGTs was much lower in old mice, regardless of the presentation level. Second, in the majority of phasic units, recovery of response to the stimulus after the silent gap was of a lower magnitude and much slower in units from old mice. Finally, the neuronal map representing response latency versus best frequency was found to be altered in the old IC. These results demonstrate a central auditory system correlate for age-related decline in temporal processing at the level of the auditory midbrain.     

Functional lateralization for auditory temporal processing in male and female rats.

In 3 studies, adult male rats showed significantly better discrimination of tone sequences with the right ear than with the left ear. This result parallels similar findings of left-hemisphere specialization for auditory temporal processing in humans and nonhuman primates. Furthermore, because clinical evidence supports a link between specialization of the left hemisphere for auditory temporal processing and for speech processing, these results may reflect evolutionary precursors to left-hemisphere language specialization. Because male rats showed a stronger ear advantage than female rats, the findings may relate to evidence of a stronger right ear advantage in men than in women. Finally, results suggest that neonatal handling enhances lateralization for auditory temporal processing in both sexes. Combined results implicate neuroendocrine mechanisms as important factors in the development of lateralization for auditory temporal processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Left planum temporale surface correlates with functional dominance during story listening

The relationship between anatomical asymmetry of the planum temporale (PT) and functional lateralization for language comprehension was studied in 14 normal volunteers, including five left-handers (LH). PT surfaces and asymmetry were measured in each subject using structural MRI, while functional lateralization was assessed on individual regional cerebral blood flow (rCBF) difference images of a PET-H2(15)O activation protocol in which a story listening condition was contrasted with a control state. Significant positive correlations were found between the left PT surface and the amount of NrCBF increase during the story listening in the left superior temporal gyrus as well as with the left-right activation index in the superior temporal and the temporal pole. Functional imaging data were correlated neither with the right PT surface nor with the right-left PT surface asymmetry index. However the latter index was correlated with handedness scores. The present results indicate that the size of the left PT is the relevant anatomical landmark for language dominance, and demonstrate that anatomical asymmetries are part of the functional variability for language.     

Cerebral lateralization and cognitive functioning in patients with congenital adrenal hyperplasia.

A battery of tests was administered to 17 patients with congenital adrenal hyperplasia (CAH) and 17 normal controls to investigate the effect of prenatal androgen exposure on cerebral lateralization and cognitive performance. Individuals were compared on measures of hand preference, verbal and performance IQ, and temporal processing asymmetry. A higher incidence of left-handedness was found among CAH participants. CAH individuals exhibited higher performance IQs as opposed to verbal IQs. Temporal processing asymmetries were investigated using an auditory gap detection task. Measures of reaction time and response error revealed a right-ear, therefore left-hemisphere, advantage for gap detection. This right-ear advantage did not differ between CAH individuals and controls. Results partially support the hypothesis that prenatal androgen exposure causes a shift in cerebral lateralization toward right-hemisphere dominance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional MRI lateralization of memory in temporal lobe epilepsy

OBJECTIVE: To determine the feasibility of using functional magnetic resonance imaging (fMRI) to detect asymmetries in the lateralization of memory activation in patients with temporal lobe epilepsy (TLE). BACKGROUND: Assessment of mesial temporal lobe function is a critical aspect of the preoperative evaluation for epilepsy surgery, both for predicting postoperative memory deficits and for seizure lateralization. fMRI offers several potential advantages over the current gold standard, intracarotid amobarbital testing (IAT). fMRI has already been successfully applied to language lateralization in TLE. METHODS: fMRI was carried out in eight normal subjects and 10 consecutively recruited patients with TLE undergoing preoperative evaluation for epilepsy surgery. A complex visual scene encoding task known to activate mesial temporal structures was used during fMRI. Asymmetry ratios for mesial temporal activation were calculated, using regions of interest defined in normals. Patient findings were compared with the results of IAT performed as part of routine clinical evaluation. RESULTS: Task activation was nearly symmetric in normal subjects, whereas in patients with TLE, significant asymmetries were observed. In all nine patients in whom the IAT result was interpretable, memory asymmetry by fMRI concurred with the findings of IAT including two patients with paradoxical IAT memory lateralization ipsilateral to seizure focus. CONCLUSIONS: fMRI can be used to detect asymmetries in memory activation in patients with TLE. Because fMRI studies are noninvasive and provide excellent spatial resolution for functional activation, these preliminary results suggest a promising role for fMRI in improving the preoperative evaluation for epilepsy surgery.     

An MEG study of picture naming

The purpose of this study was to relate a psycholinguistic processing model of picture naming to the dynamics of cortical activation during picture naming. The activation was recorded from eight Dutch subjects with a whole-head neuromagnetometer. The processing model, based on extensive naming latency studies, is a stage model. In preparing a picture"s name, the speaker performs a chain of specific operations. They are, in this order, computing the visual percept, activating an appropriate lexical concept, selecting the target word from the mental lexicon, phonological encoding, phonetic encoding, and initiation of articulation. The time windows for each of these operations are reasonably well known and could be related to the peak activity of dipole sources in the individual magnetic response patterns. The analyses showed a clear progression over these time windows from early occipital activation, via parietal and temporal to frontal activation. The major specific findings were that (1) a region in the left posterior temporal lobe, agreeing with the location of Wernicke"s area, showed prominent activation starting about 200 msec after picture onset and peaking at about 350 msec (i.e., within the stage of phonological encoding), and (2) a consistent activation was found in the right parietal cortex, peaking at about 230 msec after picture onset, thus preceding and partly overlapping with the left temporal response. An interpretation in terms of the management of visual attention is proposed.     

Using mismatch negativity to study central auditory processing in developmental language and literacy impairments: Where are we, and where should we be going?

A popular theoretical account of developmental language and literacy disorders implicates poor auditory temporal processing in their etiology, but evidence from studies using behavioral measures has yielded inconsistent results. The mismatch negativity (MMN) component of the auditory event-related potential has been recommended as an alternative, relatively objective, measure of the brain's ability to discriminate sounds that is suitable for children with limited attention or motivation. A literature search revealed 26 studies of the MMN in individuals with dyslexia or specific language impairment and 4 studies of infants or children at familial risk of these disorders. Findings were highly inconsistent. Overall, attenuation of the MMN and atypical lateralization in the clinical group were most likely to be found in studies using rapidly presented stimuli, including nonverbal sounds. The MMN literature offers tentative support for the hypothesis that auditory temporal processing is impaired in language and literacy disorders, but the field is plagued by methodological inconsistencies, low reliability of measures, and low statistical power. The article concludes with recommendations for improving this state of affairs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deviant auditory stimuli activate human left and right auditory cortex differently

Infrequent "deviant' auditory stimuli embedded in a homogeneous sequence of "standard' sounds evoke a neuromagnetic mismatch field (MMF), which is assumed to reflect automatic change detection in the brain. We investigated whether MMFs would reveal hemispheric differences in cortical auditory processing. Seven healthy adults were studied with a whole-scalp neuromagnetometer. The sound sequence, delivered to one ear at time, contained three infrequent deviants (differing from standards in duration, frequency, or interstimulus interval) intermixed with standard tones. MMFs peaked 9-34 msec earlier in the right than in the left hemisphere, irrespective of the stimulated ear. Whereas deviants activated only one MMF source in the left hemisphere, two temporally overlapping but spatially separate sources, one in the temporal lobe and another in the inferior parietal cortex, were necessary to explain the right-hemisphere MMFs. We suggest that the bilateral MMF components originating in the supratemporal cortex are feature specific whereas the right-hemisphere parietal component reflects more global auditory change detection. The results imply hemispheric differences in sound processing and suggest stronger involvement of the right than the left hemisphere in change detection.     

Auditory and visual word processing studied with fMRI

Brain activations associated with semantic processing of visual and auditory words were investigated using functional magnetic resonance imaging (fMRI). For each form of word presentation, subjects performed two tasks: one semantic, and one nonsemantic. The semantic task was identical for both auditory and visual presentation: single words were presented and subjects determined whether the word was concrete or abstract. In the nonsemantic task for auditory words, subjects determined whether the word had one syllable or multiple syllables. In the nonsemantic task for visual words, subjects determined whether the word was presented in lower case or upper case. There was considerable overlap in where auditory and visual word semantic processing occurred. Visual and auditory semantic tasks both activated the left inferior frontal (BA 45), bilateral anterior prefrontal (BA 10, 46), and left premotor regions (BA 6) and anterior SMA (BA 6, 8). Left posterior temporal (middle temporal and fusiform gyrus) and predominantly right-sided cerebellar activations were observed during the auditory semantic task but were not above threshold during visual word presentation. The data, when averaged across subjects, did not show obligatory activation of left inferior frontal and temporal language areas during nonsemantic word tasks. Individual subjects showed differences in the activation of the inferior frontal region while performing the same task, even though they showed similar response latency and accuracy.     

Representation of spectral and temporal sound features in three cortical fields of the cat. Similarities outweigh differences

This study investigates the degree of similarity of three different auditory cortical areas with respect to the coding of periodic stimuli. Simultaneous single- and multiunit recordings in response to periodic stimuli were made from primary auditory cortex (AI), anterior auditory field (AAF), and secondary auditory cortex (AII) in the cat to addresses the following questions: is there, within each cortical area, a difference in the temporal coding of periodic click trains, amplitude-modulated (AM) noise bursts, and AM tone bursts? Is there a difference in this coding between the three cortical fields? Is the coding based on the temporal modulation transfer function (tMTF) and on the all-order interspike-interval (ISI) histogram the same? Is the perceptual distinction between rhythm and roughness for AM stimuli related to a temporal versus spatial representation of AM frequency in auditory cortex? Are interarea differences in temporal response properties related to differences in frequency tuning? The results showed that: 1) AM stimuli produce much higher best modulation frequencies (BMFs) and limiting rates than periodic click trains. 2) For periodic click trains and AM noise, the BMFs and limiting rates were not significantly different for the three areas. However, for AM tones the BMF and limiting rates were about a factor 2 lower in AAF compared with the other areas. 3) The representation of stimulus periodicity in ISIs resulted in significantly lower mean BMFs and limiting rates compared with those estimated from the tMTFs. The difference was relatively small for periodic click trains but quite large for both AM stimuli, especially in AI and AII. 4) Modulation frequencies <20 Hz were represented in the ISIs, suggesting that rhythm is coded in auditory cortex in temporal fashion. 5) In general only a modest interdependence of spectral- and temporal-response properties in AI and AII was found. The BMFs were correlated positively with characteristic frequency in AAF. The limiting rate was positively correlated with the frequency-tuning curve bandwidth in AI and AII but not in AAF. Only in AAF was a correlation between BMF and minimum latency was found. Thus whereas differences were found in the frequency-tuning curve bandwidth and minimum response latencies among the three areas, the coding of periodic stimuli in these areas was fairly similar with the exception of the very poor representation of AM tones in AII. This suggests a strong parallel processing organization in auditory cortex.     

Temporal and spectral sensitivity of complex auditory neurons in the nucleus HVc of male zebra finches

Complex vocalizations, such as human speech and birdsong, are characterized by their elaborate spectral and temporal structure. Because auditory neurons of the zebra finch forebrain nucleus HVc respond extremely selectively to a particular complex sound, the bird's own song (BOS), we analyzed the spectral and temporal requirements of these neurons by measuring their responses to systematically degraded versions of the BOS. These synthetic songs were based exclusively on the set of amplitude envelopes obtained from a decomposition of the original sound into frequency bands and preserved the acoustical structure present in the original song with varying degrees of spectral versus temporal resolution, which depended on the width of the frequency bands. Although both excessive temporal or spectral degradation eliminated responses, HVc neurons responded well to degraded synthetic songs with time-frequency resolutions of approximately 5 msec or 200 Hz. By comparing this neuronal time-frequency tuning with the time-frequency scales that best represented the acoustical structure in zebra finch song, we concluded that HVc neurons are more sensitive to temporal than to spectral cues. Furthermore, neuronal responses to synthetic songs were indistinguishable from those to the original BOS only when the amplitude envelopes of these songs were represented with 98% accuracy. That level of precision was equivalent to preserving the relative time-varying phase across frequency bands with resolutions finer than 2 msec. Spectral and temporal information are well known to be extracted by the peripheral auditory system, but this study demonstrates how precisely these cues must be preserved for the full response of high-level auditory neurons sensitive to learned vocalizations.     

Side of seizure focus predicts left medial temporal lobe activation during verbal encoding

OBJECTIVE: Functional MRI (FMRI) was used to investigate the effect of medial temporal lobe (MTL) pathology on activation of language encoding areas in patients with temporal lobe epilepsy (TLE). METHODS: Whole-brain FMRI was obtained. Twenty-eight patients with either left TLE (LTLE) or right TLE (RTLE) performed a semantic decision task alternating with an auditory perceptual task. RESULTS: Activation of language areas in the frontal and parietal lobes was similar in both groups, with no group differences in the total number of active voxels. However, the RTLE group showed much stronger activation of the left MTL, including the hippocampus, parahippocampal gyrus, and collateral sulcus, than did the LTLE group. CONCLUSIONS: Activation of the left MTL during semantic encoding discriminates patients with RTLE and LTLE. This FMRI technique may potentially be of use in determining memory lateralization and for predicting the side of seizure focus in TLE.     

Intensity coding of auditory stimuli: an fMRI study

The effect of stimulus intensity (sound pressure level, SPL) of auditory stimuli on the BOLD response in the auditory cortex was investigated in 14 young and healthy subjects, with no hearing abnormalities, using echo-planar, functional magnetic resonance imaging (fMRI) during a verbal and a non-verbal auditory discrimination task. The stimuli were presented block-wise at three different intensities: 95, 85 and 75 dB (SPL). All subjects showed fMRI signal increases in superior temporal gyrus (STG) covering primary and secondary auditory cortex. Most importantly, the spatial extent of the fMRI response in STG increased with increasing stimulus intensity. It is hypothesized that spreading of excitation is associated with the encoding of increasing stimulus intensity levels. In addition, we found bifrontal activation supposedly evoked by the auditory-articulary loop of working memory. The results presented here should assist in the design of optimal activation strategies for studying the auditory cortex with fMRI paradigms and may help in understanding intensity coding of auditory stimuli.     

Reliability of low-frequency auditory stimulation studies associated with technetium-99m hexamethylpropylene amine oxime single-photon emission tomography

Development of auditory stimulation tests associated with single-photon emission tomography (SPET) shows evidence of variations in perfusion related to the stimuli. Three brain SPET examinations with technetium-99m hexamethylpropylene amine oxime were performed on eight right-handed adults with normal hearing, the first one without stimulation and the other two associated with a 500-Hz/30-dB stimulation of the right ear. Temporal regions of interest covering auditory areas, as well as parietal ones (internal control), were drawn on three successive coronal slices. A cortico-cerebellar index R was calculated, and the variation in activity was defined for each subject using the ratio R poststimulation--R prestimulation/R prestimulation. A significant increase in the temporal cortex count occurred in all subjects. This increase was bilateral, except for one subject in whom it was not significant on the right side. This result recurred during the second stimulation study. Overall the response of the left temporal cortex was stronger, although the asymmetry was not significant. The asymmetry repeated itself after each stimulation. The perfusion response is globally reliable in our study. We must ascertain how sensitive this test is with regard to deaf adults and adults with normal hearing before extending its use to children.     

Language lateralization of Chinese-English bilingual patients with temporal lobe epilepsy: A functional MRI study.

Functional MRI was used to examine language lateralization of Chinese characters and English words associated with temporal lobe epilepsy (TLE) in Chinese-English bilinguals with left or right TLE. The results suggest that the neural basis of processing Chinese and English seems to be different, as normal controls demonstrated left hemispheric lateralization in reading English words but bi-hemispheric lateralization in reading Chinese characters. This difference in the neural bases of Chinese and English processing was found to affect the patterns in change-of-language processing associated with TLE. That is, whereas left-TLE patients were more likely than right-TLE patients to demonstrate a bi-hemispheric language involvement in reading English, both left- and right-TLE patients demonstrated primarily bilateral hemispheric involvement for reading Chinese characters. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex-Linked Differences in the Anatomy of the Perisylvian Language Cortex: A Volumetric MRI Study of Gray Matter Volumes.

Perisylvian regions important for auditory processing include Heschl's gyrus (HG), the planum temporale (PT), the posterior superior temporal gyrus (pSTG), and the posterior ascending ramus (PAR). Sex-linked differences in language functions and anatomy have been suggested. To examine sex-linked differences, the authors used MRI to measure HG, PT, pSTG, and PAR volumes. Sex differences were found in right HG and right pSTG volumes but not in the left volumes of these structures. For the PT, there were sex differences in asymmetry; women exhibited leftward asymmetry of the PT, whereas men did not exhibit PT asymmetry. These findings suggest that there are sex-linked differences in the anatomy of primary and association auditory cortices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Malpractice claims against radiologists. Analysis of the five-year period 1993-1997

OBJECTIVES: Landau-Kleffner Syndrome (LKS) is an epileptic syndrome characterised by a deficit in language comprehension and production, paroxysmal epileptiform activity in the posterior temporal leads, and by the inconsistent presence of epileptic fits. Its interest lies in the fact that it stands as a model for the study of interference of epileptiform activity on cognitive function, although the pathophysiology of the decline in language skills that follows its onset has not yet been clarified. METHODS: We have recorded spike-triggered auditory evoked responses in a group of 6 children with LKS, to investigate whether the occurrence of individual EEG paroxysms is able per se to induce a decline in the response of the auditory cortex. RESULTS: Results have indicated that left hemisphere spikes are associated with a greater reduction in amplitude and an increase in latency of the NI, than spikes occurring in the right hemisphere. No stable change in the evoked response has been detected outside of the EEG paroxysm. CONCLUSIONS: We postulate EEG interictal activity is able to induce impairment in processing auditory information and that this may play a role in the pathogenesis of language deficit in LKS.     

Failure of dominant left-hemispheric activation to right-ear stimulation in schizophrenia

Schizophrenia is associated with an absence of the lateralizations that typify the human brain. Previous evidence emphasized structural changes, particularly reduced asymmetry in extension and surface of the planum temporale, although gross structural deviations occur only in a minority of patients. The present study describes an absence of lateralization on a robust functional measure that characterized schizophrenia patients: healthy subjects but not schizophrenics displayed a contralateral left-hemispheric dominance of the auditory evoked magnetic field to right-ear auditory stimulation. Absence of contralateral dominance in response to auditory stimuli among schizophrenia patients may indicate a failure to establish unequivocal left-hemispheric dominance of the phonological loop as hypothesized by Crow.     

Ontogeny of cerebral dominance: Evidence from time-sharing asymmetry in children.

Used a dual-task procedure as a measure of speech lateralization in 151 normal, right-handed, 3–12 yr old children. Ss engaged in unimanual finger tapping with and without concurrent speech. It was hypothesized that if speech is left lateralized, talking should disrupt right-hand tapping (an instance of intrahemispheric interference) more than left-hand tapping (an instance of interhemispheric interference). Results for 2 different verbal tasks show the predicted overall asymmetry but no developmental trend in degree of asymmetry. The data suggest that lateralization is as marked in young children as in older children. About 70% of the Ss showed the predicted effect; there was no significant change in incidence as a function of grade level. Analyses of verbal production indicated that the performance asymmetry could not be attributed to an asymmetrical trade-off between talking and tapping. No sex differences in performance asymmetry were found. The results contradict the traditional model of progressive lateralization but corroborate the developmental invariance frequently observed using perceptual measures of language lateralization. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Speech-evoked activity in primary auditory cortex: effects of voice onset time

Neural encoding of temporal speech features is a key component of acoustic and phonetic analyses. We examined the temporal encoding of the syllables /da/ and /ta/, which differ along the temporally based, phonetic parameter of voice onset time (VOT), in primary auditory cortex (A1) of awake monkeys using concurrent multilaminar recordings of auditory evoked potentials (AEP), the derived current source density, and multiunit activity. A general sequence of A1 activation consisting of a lamina-specific profile of parallel and sequential excitatory and inhibitory processes is described. VOT is encoded in the temporal response patterns of phase-locked activity to the periodic speech segments and by "on" responses to stimulus and voicing onset. A transformation occurs between responses in the thalamocortical (TC) fiber input and A1 cells. TC fibers are more likely to encode VOT with "on" responses to stimulus onset followed by phase-locked responses during the voiced segment, whereas A1 responses are more likely to exhibit transient responses both to stimulus and voicing onset. Relevance to subcortical speech processing, the human AEP and speech psychoacoustics are discussed. A mechanism for categorical differentiation of voiced and unvoiced consonants is proposed.