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Biomedical subjects

J D Warren

Publications and source records attributed to J D Warren.

At least 19 recordsLinked to original sources
PubMed2006

Processing the acoustic effect of size in speech sounds.

The length of a vocal tract is reflected in the sound it is producing. The length of the vocal tract is correlated with body size and humans are very good at making size judgments based on the acoustic effect of vocal tract length only. Here we investigate the underlying mechanism for processing this main auditory cue to size information in the human brain. Sensory encoding of the acoustic effect of vocal tract length (VTL) depends on a time-stabilized spectral scaling mechanism that is independent of glottal pulse rate (GPR, or voice pitch); we provide evidence that a potential neural correlate for such a mechanism exists in the medial geniculate body (MGB). The perception of the acoustic effect of speaker size is influenced by GPR suggesting an interaction between VTL and GPR processing; such an interaction occurs only at the level of non-primary auditory cortex in planum temporale and anterior superior temporal gyrus. Our findings support a two-stage model for the processing of size information in speech based on an initial stage of sensory analysis as early as MGB, and a neural correlate of the perception of source size in non-primary auditory cortex.

Acoustic Stimulation↗
PubMed2006

Musical hallucinations in a musician.

The experience of music is difficult to study objectively. Here we describe a detailed analysis of musical hallucinations developing after a probable brainstem stroke in an 83 year old musician who was able to describe and notate the hallucinations. The hallucinations comprised simple, repetitive melodic and rhythmic motifs that were combined apparently randomly without definite tonality, large-scale structure, or timbre. This observation is consistent with the proposal that musical hallucinations represent abnormal spontaneous activity in auditory cortical areas beyond the primary auditory cortex. This activity may generate novel musical motifs.

Aged, 80 and over↗
PubMed2006

Human brain mechanisms for the early analysis of voices.

In this functional magnetic resonance imaging study, we investigated human brain mechanisms that are involved in the analysis of voices as sound sources and in the pre-semantic analysis of voice information. The source of the voice was altered by changing the speaker, and the salience of the voice was altered by changing the amount of spectrotemporal detail. We identified a mechanism for detecting a change in the source of the voice in the posterior superior temporal lobe and anatomically distinct mechanisms for the detailed analysis of voice information in a bilateral network extending from the posterior to the anterior superior temporal lobe surrounding the superior temporal sulcus. The findings are consistent with a processing hierarchy in which general source attributes are analyzed in the posterior superior temporal lobe, abstraction of voice identity features occurs in posterior superior temporal sulcus, and further analysis of voice information occurs in anterior superior temporal sulcus and higher order cortices in the middle and anterior temporal lobe.

Adult↗
PubMed2005

Brain biopsy in dementia.

Brain biopsy has an uncertain role in the diagnosis of dementia. Here we report a retrospective analysis of 90 consecutive cerebral biopsies undertaken for the investigation of dementia in adults at a tertiary referral centre between 1989 and 2003. In most cases (90%), biopsy consisted of a right frontal full thickness resection of cortex, white matter and overlying leptomeninges. Fifty-seven per cent of biopsies were diagnostic: the most frequent diagnoses were Alzheimer's disease (18%), Creutzfeldt-Jakob disease (12%) and inflammatory disorders (9%). Other diagnoses in individual patients included Pick's disease, corticobasal degeneration and other tauopathies, Lewy body dementia, multiple sclerosis, Whipple's disease, progressive multifocal leucoencephalopathy, cerebral autosomal dominant arteriopathy with subcortical ischaemic leucoencephalopathy, vasculopathies and paraneoplastic encephalopathy. The most frequent biopsy finding in the non-diagnostic group and for the series as a whole (37%) was non-specific gliosis variably affecting both cortex and white matter. Complications (11%) included seizures, intracranial and wound infections, and intracranial haemorrhage; there were no deaths or lasting neurological sequelae attributable to the procedure. No trends in diagnostic yield or complication rate over the course of the series were identified. Information obtained at biopsy determined treatment in 11%. A raised cerebrospinal fluid cell count was the only robust predictor of a potentially treatable (inflammatory) process at biopsy. The constellation of behavioural change, raised CSF protein and matched oligoclonal bands in CSF and serum was associated with non-specific gliosis at biopsy. This series underlines the value of cerebral biopsy in the diagnosis of dementia, and suggests that certain clinical and laboratory features may be useful in guiding the decision to proceed to brain biopsy where a treatable disease cannot be excluded by other means.

Adolescent↗
PubMed2005

Analysis of the spectral envelope of sounds by the human brain.

Spectral envelope is the shape of the power spectrum of sound. It is an important cue for the identification of sound sources such as voices or instruments, and particular classes of sounds such as vowels. In everyday life, sounds with similar spectral envelopes are perceived as similar: we recognize a voice or a vowel regardless of pitch and intensity variations, and we recognize the same vowel regardless of whether it is voiced (a spectral envelope applied to a harmonic series) or whispered (a spectral envelope applied to noise). In this functional magnetic resonance imaging (fMRI) experiment, we investigated the basis for analysis of spectral envelope by the human brain. Changing either the pitch or the spectral envelope of harmonic sounds produced similar activation within a bilateral network including Heschl's gyrus and adjacent cortical areas in the superior temporal lobe. Changing the spectral envelope of continuously alternating noise and harmonic sounds produced additional right-lateralized activation in superior temporal sulcus (STS). Our findings show that spectral shape is abstracted in superior temporal sulcus, suggesting that this region may have a generic role in the spectral analysis of sounds. These distinct levels of spectral analysis may represent early computational stages in a putative anteriorly directed stream for the categorization of sound.

Adult↗
PubMed2004

A presenilin 1 R278I mutation presenting with language impairment.

Presenilin (PSEN)1 mutations are responsible for many cases of autosomal dominant Alzheimer disease (AD), although the clinical spectrum has not been fully defined. The authors describe two members of a kindred with a novel PSEN1 mutation (R278I) presenting with language impairment and relative preservation of memory. Screening for PSEN1 mutations may be appropriate in cases of familial dementia even where the clinical phenotype is not typical of AD.

Alzheimer Disease↗
PubMed2004

Young onset dementia.

Young onset dementia is a challenging clinical problem with potentially devastating medical and social consequences. The differential diagnosis is wide, and includes a number of rare sporadic and hereditary diseases. However, accurate diagnosis is often possible, and all patients should be thoroughly investigated to identify treatable processes. This review presents an approach to the diagnosis, investigation, and management of patients with young onset dementia, with particular reference to common and treatable causes.

Age of Onset↗
PubMed2003

Separating pitch chroma and pitch height in the human brain.

Musicians recognize pitch as having two dimensions. On the keyboard, these are illustrated by the octave and the cycle of notes within the octave. In perception, these dimensions are referred to as pitch height and pitch chroma, respectively. Pitch chroma provides a basis for presenting acoustic patterns (melodies) that do not depend on the particular sound source. In contrast, pitch height provides a basis for segregation of notes into streams to separate sound sources. This paper reports a functional magnetic resonance experiment designed to search for distinct mappings of these two types of pitch change in the human brain. The results show that chroma change is specifically represented anterior to primary auditory cortex, whereas height change is specifically represented posterior to primary auditory cortex. We propose that tracking of acoustic information streams occurs in anterior auditory areas, whereas the segregation of sound objects (a crucial aspect of auditory scene analysis) depends on posterior areas.

Acoustic Stimulation↗
PubMed2003

Distinct mechanisms for processing spatial sequences and pitch sequences in the human auditory brain.

Perception of the acoustic world requires the simultaneous processing of the acoustic patterns associated with sound objects and their location in space. In this functional magnetic resonance experiment, we investigated the human brain areas engaged in the analysis of pitch sequences and sequences of acoustic spatial locations in a paradigm in which both could be varied independently. Subjects were presented with sequences of sounds in which the individual sounds were regular interval noises with variable pitch. Positions of individual sounds were varied using a virtual acoustic space paradigm during scanning. Sound sequences with changing pitch specifically activated lateral Heschl's gyrus (HG), anterior planum temporale (PT), planum polare, and superior temporal gyrus anterior to HG. Sound sequences with changing spatial locations specifically activated posteromedial PT. These results demonstrate directly that distinct mechanisms for the analysis of pitch sequences and acoustic spatial sequences exist in the human brain. This functional differentiation is evident as early as PT: within PT, pitch pattern is processed anterolaterally and spatial location is processed posteromedially. These areas may represent human homologs of macaque lateral and medial belt, respectively.

Acoustic Stimulation↗
PubMed2000

A SPECT study of the anatomy of transient global amnesia.

This report describes single photon emission tomography (SPECT) evidence of transient, relative hypoperfusion of the right basal ganglia and left temporal lobe in a 60-year-old man studied during the acute phase of classical transient global amnesia (TGA). The findings are interpreted in the light of previous reports indicating that involvement of the right hemisphere or both cerebral hemispheres consistently predicts severe retrograde amnesia, in addition to the typical loss of anterograde memory observed during TGA. These deficits involving the right hemisphere and left temporal lobe may reflect disruption of circuits mediating episodic memory retrieval and memory encoding, respectively.

Amnesia, Retrograde↗
PubMed2000

Expressive language disorder after infarction of left lentiform nucleus.

A 53 year old bilingual woman presented with apraxia of speech and writing in English and German after ischaemic infarction of the left posterior lentiform nucleus. Detailed language assessment revealed impairments of articulation, verbal fluency, auditory repetition, interpretation of complex semantic relationships, formulation of definitions and verbal short-term memory. The case illustrates the role of the basal ganglia in speech planning, word retrieval and verbal short-term memory.

Apraxias↗
PubMed2000

Acoustic scattering by benthic and planktonic shelled animals.

Acoustic backscattering measurements and associated scattering modeling were recently conducted on a type of benthic shelled animal that has a spiral form of shell (Littorina littorea). Benthic and planktonic shelled animals with this shape occur on the seafloor and in the water column, respectively, and can be a significant source of acoustic scattering in the ocean. Modeling of the scattering properties allows reverberation predictions to be made for sonar performance predictions as well as for detection and classification of animals for biological and ecological applications. The studies involved measurements over the frequency range 24 kHz to 1 MHz and all angles of orientation in as small as 1 degree increments. This substantial data set is quite revealing of the physics of the acoustic scattering by these complex shelled bodies and served as a basis for the modeling. Specifically, the resonance structure of the scattering was strongly dependent upon angle of orientation and could be traced to various types of rays (e.g., subsonic Lamb waves and rays entering the opercular opening). The data are analyzed in both the frequency and time domain (compressed pulse processing) so that dominant scattering mechanisms could be identified. Given the complexity of the animal body (irregular elastic shell with discontinuities), approximate scattering models are used with only the dominant scattering properties retained. Two models are applied to the data, both approximating the body as a deformed sphere: (1) an averaged form of the exact modal-series-based solution for the spherical shell, which is used to estimate the backscattering by a deformed shell averaged over all angles of orientation, and produces reasonably accurate predictions over all k1a(esr) (k1 is the acoustic wave number of the surrounding water and a(esr) is the equivalent spherical radius of the body), and (2) a ray-based formula which is used to estimate the scattering at fixed angle of orientation, but only for high k1a(esr). The ray-based model is an extension of a model recently developed for the shelled zooplankton Limacina retroversa that has a shape similar to that of the Littorina littorea but swims through the water [Stanton et al., J. Acoust. Soc. Am. 103, 236-253 (1998b)]. Applications of remote detection and classification of the seafloor and water column in the presence of shelled animals are discussed.

Acoustics↗
PubMed1999

The silent period after magnetic brain stimulation in generalized tetanus.

The cortical silent period has not previously been studied in tetanus. Transcranial magnetic brain stimulation in a patient with generalized tetanus revealed enlarged electromyographic (EMG) responses and absence or reduction of the late phase of EMG silence following the motor evoked potential in sternomastoid and biceps brachii muscles. Following clinical recovery, the silent period returned to normal. This observation is interpreted as evidence of impaired inhibitory mechanisms at multiple levels of the nervous system, including the cortex, in generalized tetanus.

Electric Stimulation↗