Biomedical subjects

Ingrid S Johnsrude

Publications and source records attributed to Ingrid S Johnsrude.

9 recordsLinked to original sources

PubMed2003

Hierarchical processing in spoken language comprehension.

Understanding spoken language requires a complex series of processing stages to translate speech sounds into meaning. In this study, we use functional magnetic resonance imaging to explore the brain regions that are involved in spoken language comprehension, fractionating this system into sound-based and more abstract higher-level processes. We distorted English sentences in three acoustically different ways, applying each distortion to varying degrees to produce a range of intelligibility (quantified as the number of words that could be reported) and collected whole-brain echo-planar imaging data from 12 listeners using sparse imaging. The blood oxygenation level-dependent signal correlated with intelligibility along the superior and middle temporal gyri in the left hemisphere and in a less-extensive homologous area on the right, the left inferior frontal gyrus (LIFG), and the left hippocampus. Regions surrounding auditory cortex, bilaterally, were sensitive to intelligibility but also showed a differential response to the three forms of distortion, consistent with sound-form-based processes. More distant intelligibility-sensitive regions within the superior and middle temporal gyri, hippocampus, and LIFG were insensitive to the acoustic form of sentences, suggesting more abstract nonacoustic processes. The hierarchical organization suggested by these results is consistent with cognitive models and auditory processing in nonhuman primates. Areas that were particularly active for distorted speech conditions and, thus, might be involved in compensating for distortion, were found exclusively in the left hemisphere and partially overlapped with areas sensitive to intelligibility, perhaps reflecting attentional modulation of auditory and linguistic processes.

Acoustic Stimulation↗

PubMed2003

The neuroanatomical and functional organization of speech perception.

A striking property of speech perception is its resilience in the face of acoustic variability (among speech sounds produced by different speakers at different times, for example). The robustness of speech perception might, in part, result from multiple, complementary representations of the input, which operate in both acoustic-phonetic feature-based and articulatory-gestural domains. Recent studies of the anatomical and functional organization of the non-human primate auditory cortical system point to multiple, parallel, hierarchically organized processing pathways that involve the temporal, parietal and frontal cortices. Functional neuroimaging evidence indicates that a similar organization might underlie speech perception in humans. These parallel, hierarchical processing 'streams', both within and across hemispheres, might operate on distinguishable, complementary types of representations and subserve complementary types of processing. Two long-opposing views of speech perception have posited a basis either in acoustic feature processing or in gestural motor processing; the view put forward here might help reconcile these positions.

Acoustic Stimulation↗

PubMed2002

The processing of temporal pitch and melody information in auditory cortex.

An fMRI experiment was performed to identify the main stages of melody processing in the auditory pathway. Spectrally matched sounds that produce no pitch, fixed pitch, or melody were all found to activate Heschl's gyrus (HG) and planum temporale (PT). Within this region, sounds with pitch produced more activation than those without pitch only in the lateral half of HG. When the pitch was varied to produce a melody, there was activation in regions beyond HG and PT, specifically in the superior temporal gyrus (STG) and planum polare (PP). The results support the view that there is hierarchy of pitch processing in which the center of activity moves anterolaterally away from primary auditory cortex as the processing of melodic sounds proceeds.

Acoustic Stimulation↗

PubMed2002

Preference formation and working memory in Parkinson's disease and normal ageing.

Recent studies in rats have suggested that the amygdala and the dorsal striatum may be differentially involved in the formation of stimulus-reward associations and stimulus-response associations, respectively. In a recent study in humans, conditioned preference learning deficits were observed in a group of patients with damage to the amygdala formation. In this study, patients with Parkinson's disease, which is known to involve pathology of the dorsal striatum, were tested on the same conditioned preference task, together with a group of patients with circumscribed lesions of the frontal lobe. Unlike patients with frontal lobe damage, patients with Parkinson's disease did not exhibit conditioned preferences. However, in this respect their behaviour was indistinguishable from that of age-matched (older) control subjects. In keeping with previous literature, working memory deficits were observed in both patients with Parkinson's disease and patients with frontal-lobe lesions. Compared to young control subjects, a strong increase in preference for familiar, versus novel, items was observed in both patients with Parkinson's disease and in older control subjects. Such a familiarity effect appears to overshadow the conditioning manipulation employed in this task and, therefore, preclude the expression of conditioned preferences in older subjects. These results suggest that there is a developmental progression in the degree to which different mechanisms of 'learning to like' are important over the life span.

Adult↗

PubMed2002

The problem of functional localization in the human brain.

Functional imaging gives us increasingly detailed information about the location of brain activity. To use this information, we need a clear conception of the meaning of location data. Here, we review methods for reporting location in functional imaging and discuss the problems that arise from the great variability in brain anatomy between individuals. These problems cause uncertainty in localization, which limits the effective resolution of functional imaging, especially for brain areas involved in higher cognitive function.

Brain↗

PubMed2002

Detecting residual cognitive function in persistent vegetative state.

Despite converging agreement about the definition of persistent vegetative state, recent reports have raised concerns about the accuracy of diagnosis in some patients, and the extent to which, in a selection of cases, residual cognitive functions may remain undetected. Objective assessment of residual cognitive function can be extremely difficult as motor responses may be minimal, inconsistent, and difficult to document in many patients, or may be undetectable in others because no cognitive output is possible. Here we describe strategies for using H(2)(15)O positron emission tomography activation studies to study covert cognitive processing in patients with a clinical diagnosis of persistent vegetative state. Three cases are described in detail. Of these, two exhibited clear and predicted regional cerebral blood flow responses during well-documented activation paradigms (face recognition and speech perception) which have been shown to produce specific, robust and reproducible activation patterns in normal volunteers. Some months after scanning, both patients made a significant recovery. In a third case, blood flow data were acquired during a speech perception task, although methodological difficulties precluded any systematic interpretation of the results. In spite of the multiple logistic and procedural problems involved, these results have major clinical and scientific implications and provide a strong basis for the systematic study of possible residual cognitive function in patients diagnosed as being in a persistent vegetative state.

Adult↗

PubMed2002

Spectral and temporal processing in human auditory cortex.

Hierarchical processing suggests that spectrally and temporally complex stimuli will evoke more activation than do simple stimuli, particularly in non-primary auditory fields. This hypothesis was tested using two tones, a single frequency tone and a harmonic tone, that were either static or frequency modulated to create four stimuli. We interpret the location of differences in activation by drawing comparisons between fMRI and human cytoarchitectonic data, reported in the same brain space. Harmonic tones produced more activation than single tones in right Heschl's gyrus (HG) and bilaterally in the lateral supratemporal plane (STP). Activation was also greater to frequency-modulated tones than to static tones in these areas, plus in left HG and bilaterally in an anterolateral part of the STP and the superior temporal sulcus. An elevated response magnitude to both frequency-modulated tones was found in the lateral portion of the primary area, and putatively in three surrounding non-primary regions on the lateral STP (one anterior and two posterior to HG). A focal site on the posterolateral STP showed an especially high response to the frequency-modulated harmonic tone. Our data highlight the involvement of both primary and lateral non-primary auditory regions.

Acoustic Stimulation↗

PubMedDate not supplied

Functional imaging of the auditory system: the use of positron emission tomography.

Modern brain imaging methods now afford unprecedented opportunities for the in vivo study of central auditory system function. Positron emission tomography (PET) has been used as a functional imaging technique for more than 15 years to study the distribution of cerebral haemodynamic changes associated with auditory stimulation, in subjects with normal and abnormal auditory function. Many of these studies concern processes related to, but not identical with, audition, such as speech perception, melodic processing and directed attention. Additionally, PET has been used to explore auditory perception in clinical populations such as cochlear implantees, neurosurgical candidates and people with tinnitus and auditory hallucinations. The spatial resolution of PET does not appear sufficient to address questions of a fine anatomical grain, e.g. exploring functional specialization within the primary and secondary auditory cortex. Nevertheless, PET has considerable potential as a tool in basic research on, and clinical assessment of, many auditory phenomena. Although functional magnetic resonance imaging can now be used for many studies for which formerly only PET was suitable, PET still possesses unique advantages. For example, it permits acquisition of data from inferior frontal and anterior temporal areas, can be used with subjects with cochlear and other implants (such as pacemakers) and can be used to map neurochemical pathways and receptors.

Auditory Cortex↗

PubMedDate not supplied

Relationships between human auditory cortical structure and function.

The human auditory cortex comprises multiple areas, largely distributed across the supratemporal plane, but the precise number and configuration of auditory areas and their functional significance have not yet been clearly established. In this paper, we discuss recent research concerning architectonic and functional organisation within the human auditory cortex, as well as architectonic and neurophysiological studies in non-human species, which can provide a broad conceptual framework for interpreting functional specialisation in humans. We review the pattern in human auditory cortex of the functional responses to various acoustic cues, such as frequency, pitch, sound level, temporal variation, motion and spatial location, and we discuss their correspondence to what is known about the organisation of the auditory cortex in other primates. There is some neuroimaging evidence of multiple tonotopically organised fields in humans and of functional specialisations of the fields in the processing of different sound features. It is thought that the primary area, on Heschl's gyrus, may have a larger involvement in processing basic sound features, such as frequency and level, and that posterior non-primary areas on the planum temporale may play a larger role in processing more spectrotemporally complex sounds. Ways in which current knowledge of auditory cortical organisation and different data analysis approaches may benefit future functional neuroimaging studies which seek to link auditory cortical structure and function are discussed.

Animals↗