Amplitopicity of the human auditory cortex: an fMRI study.

Whereas specialized frequency-encoding patterns in the human auditory cortex are generally accepted, termed tonotopicity, a similar principle of intensity encoding--amplitopicity--is debated controversially. This functional magnetic resonance imaging study describes the relationship of the activation volume and the spatial distribution of activated clusters under different sound pressure levels (SPL) across the temporal plane including the transverse temporal gyrus (TTG). Nine healthy subjects with no hearing deficiencies were investigated using an echo-planar imaging technique at 1.5 T. A boxcar stimulation paradigm was applied with a 5-Hz pulsed sine tone of 1000 Hz frequency at three SPLs of 70, 82, and 90 dB. Linear cross-correlation analysis (correlation coefficient > 0.3 corresponding to P < 0.08) of the functional data set revealed bilateral BOLD response within the auditory cortex of the nine subjects with moderate increase of activation volume for higher sound pressure levels. With increasing sound pressure a two-dimensional drift of cortical activation was observed (a) from the ventral to the dorsal edge and (b) from lateral to medial parts of TTG. This latero-medial drift therefore mimics the well-accepted principle of tonotopy for frequency-encoding neurons. This study demonstrates the existence of an amplitopic pattern of intensity-encoding neuronal clusters that in part resembles the tonotopic distribution of frequency-encoding neurons. This finding has to be integrated into the understanding of the auditory organization for the interpretation of higher auditory functions such as sound perception or speech.

fMRI of the auditory cortex in patients with unilateral carotid artery steno-occlusive disease.

PURPOSE: To examine whether an internal carotid artery (ICA) steno-occlusive disease leads to a reduced blood oxygenation level dependent (BOLD)-signal change due to a decreased vasodilatory reserve capacity. MATERIALS AND METHODS: Patients suffering from unilateral ICA stenosis or occlusion were examined using functional magnetic resonance imaging (fMRI) of the auditory cortex with a bilateral stimulation applying a pulsed 1000 Hz sine-tone. RESULTS: Compared to control subjects, who showed symmetric bilateral BOLD-responses within the auditory cortex, the ICA patients revealed either a normal bilateral cortical activation pattern or a reduced cortical activation on the steno-occluded side. This latter decrease of BOLD-signal change might indicate a depressed vasomotor reserve capacity. The observed coincidence between this asymmetric reduction in BOLD-signal and ischemic borderzone lesions on the affected side in this subgroup of patients strongly supports this assumption. CONCLUSION: This study shows that fMRI of the auditory cortex appears to have clinical merit in the workup of cerebrovascular conditions.

Is there a BOLD response of the visual cortex on stimulation of the vision-related acupoint GB 37?

PURPOSE: To determine whether or not acupuncture of guangming (GB 37) produces a significant response of the visual cortex detectable by means of functional magnetic resonance imaging (fMRI). MATERIALS AND METHODS: This study investigates the activation of the visual cortex elicited by a soft and an intensified stimulation of GB 37, an acupoint documented to influence vision-related disorders. Three different paradigms were carried out to detect any possible modulation of the Blood Oxygenation Level Dependent (BOLD)-response in the visual cortex to visual stimulation through acupuncture. RESULTS: The percentage signal changes in the visual stimulation cycles did not significantly differ before vs. during acupuncture. CONCLUSION: Whereas no BOLD-response correlating with acupuncture was detected in the visual cortex, BOLD-signal-changes in response to needle twisting were detected in different cortical areas. Further studies are necessary to clarify whether these clusters correlate to inevitable somatosensory stimulation accompanying acupuncture or represent an acupuncture-specific response.