Biomedical subjects
Publications and source records attributed to Deborah A Hall.
New evidence confirms that the auditory system encompasses temporal, parietal and frontal brain regions, some of which partly overlap with the visual system. But common assumptions about the functional homologies between sensory systems may be misleading.
Sounds that move towards us have a greater biological salience than those that move away. Recent studies in human and non-human primates have demonstrated a perceptual and behavioural priority for such looming sounds that is also reflected in an asymmetric pattern of cortical activation.
fMRI (functional magnetic resonance imaging) was used to investigate whether the growth in activation of the human auditory cortex, with increasing sound level, is discernibly different for high- and low-frequency tones. Ten volunteers were scanned whilst listening to sequences of low-frequency (0.30-kHz) tones at sound levels between 42 and 96 dB sound pressure level (SPL), and 10 whilst listening to high-frequency (4.75-kHz) tones at the same sound levels. Activation was measured in Heschl's gyrus (including primary auditory cortex) which has been shown to be most sensitive to changes in sound level. For the 0.30-kHz tone, the extent of activation was flat up to 66 dB and then showed a rapid growth which continued up to the highest level studied (96 dB SPL). In contrast, increasing the level of 4.75-kHz tones produced a steady growth in the extent of activation across the range of levels studied. These results are consistent with physiological evidence suggesting that recruitment of primary auditory cortical neurones may be different at high and low frequencies.
Hall et al. (Hall et al., 2002, Cerebral Cortex 12:140-149) recently showed that pulsed frequency-modulated tones generate considerably higher activation than their unmodulated counterparts in non-primary auditory regions immediately posterior and lateral to Heschl's gyrus (HG). Here, we use fMRI to explore the type of modulation necessary to evoke such differential activation. Carrier signals were a single tone and a harmonic-complex tone, with a 300 Hz fundamental, that were modulated at a rate of 5 Hz either in frequency, or in amplitude, to create six stimulus conditions (unmodulated, FM, AM). Relative to the silent baseline, the modulated tones, in particular, activated widespread regions of the auditory cortex bilaterally along the supra-temporal plane. When compared with the unmodulated tones, both AM and FM tones generated significantly greater activation in lateral HG and the planum temporale, replicating the previous findings. These activation patterns were largely overlapping, indicating a common sensitivity to both AM and FM. Direct comparisons between AM and FM revealed a higher magnitude of activation in response to the variation in amplitude than in frequency, plus a small part of the posterolateral region in the right hemisphere whose response was specifically AM-, and not FM-, dependent. The dominant pattern of activation was that of co-localized activation by AM and FM, which is consistent with a common neural code for AM and FM within these brain regions.
Previous neuroimaging studies generally demonstrate a growth in the cortical response with an increase in sound level. However, the details of the shape and topographic location of such growth remain largely unknown. One limiting methodological factor has been the relatively sparse sampling of sound intensities. Additionally, most studies have either analysed the entire auditory cortex without differentiating primary and non-primary regions or have limited their analyses to Heschl's gyrus (HG). Here, we characterise the pattern of responses to a 300-Hz tone presented in 6-dB steps from 42 to 96 dB sound pressure level as a function of its sound level, within three anatomically defined auditory areas; the primary area, on HG, and two non-primary areas, consisting of a small area lateral to the axis of HG (the anterior lateral area, ALA) and the posterior part of auditory cortex (the planum temporale, PT). Extent and magnitude of auditory activation increased non-linearly with sound level. In HG, the extent and magnitude were more sensitive to increasing level than in ALA and PT. Thus, HG appears to have a larger involvement in sound-level processing than does ALA or PT.
While BOLD contrast reflects hemodynamic changes within capillaries serving neural tissue, it also has a venous component. Studies that have determined the relation of large blood vessels to the activation map indicate that veins are the source of the largest response, and the most delayed in time. It would be informative if the location of these large veins could be extracted from the properties of the functional responses, since vessels are not visible in BOLD contrast images. The present study describes a method for investigating whether measures taken from the functional response can reliably predict vein location, or at least be useful in down-weighting the venous contribution to the activation response, and illustrates this method using data from one subject. We combined fMRI at 3 Tesla with high-resolution anatomic imaging and MR venography to test whether the intrinsic properties of activation time courses corresponded to tissue type. Measures were taken from a gamma fit to the functional response. Mean magnitude showed a significant effect of tissue type (p < 0.001) where CSF > veins approximately gray matter > white matter. Mean delays displayed the same ranking across tissue types (p < 0.001), except that veins > gray matter. However, measures for all tissue types were distributed across an overlapping range. A logistic regression model correctly discriminated 72% of the veins from gray matter in the absence of independent information of macroscopic vessels (ROC = 0.72). While tissue classification was not perfect for this subject, weighting the T contrast by the predicted probabilities materially reduced the venous component to the activation map.
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.
OBJECTIVE: We assessed whether specific sonographic characteristics are indicative of the extent of adenomyosis and whether fibroids alter this assessment. MATERIALS AND METHODS: Patients' records were evaluated for the diagnosis of adenomyosis determined by hysterectomy and for sonography performed within 2 months of surgery. Seventy-three sonograms were evaluated by sonologists without knowledge of the extent of adenomyosis. Sonographic categories included visualization of the endometrium, presence of a diffuse uterine process, presence of fibroids, and normal findings. Pathologic results included mild, focal, and severe adenomyosis. Histologic and sonographic categories were correlated using the chi-square and Fisher's exact tests. RESULTS: Forty-six specimens contained mild adenomyosis, 18 contained severe disease, and nine contained focal disease. Forty-one specimens contained fibroids. The endometrium was visualized in 10 cases of severe adenomyosis, seven cases of adenomyoma, and 35 cases of mild disease. Visualization of the endometrium did not relate to the severity of disease (p = 0.6). Of 18 cases of severe disease, 13 sonograms showed a diffuse process. Of nine cases of adenomyomas, no sonograms showed a diffuse process; and of 46 cases of mild disease, nine sonograms showed a diffuse process. A diffuse process was related to the severity of adenomyosis (p < 0.001). When fibroids were present, a diffuse process did not relate to the extent of adenomyosis (p = 0.01). CONCLUSION: In the absence of focal fibroids, a diffuse uterine process seen on sonography relates to the severity of adenomyosis. Fibroids limit the ability to diagnose the severity of adenomyosis. The visualization of the endometrium does not relate to the severity of adenomyosis.
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.