Physiological studies of auditory perception have not yet clearly distinguished sensory from decision processes. In this experiment, human participants identified speech sounds masked by varying levels of noise while blood oxygenation signals in the brain were recorded with functional magnetic resonance imaging (fMRI). Accuracy and response time were used to characterize the behavior of sensory and decision components of this perceptual system. Oxygenation signals in a cortical subregion just anterior and lateral to primary auditory cortex predicted accuracy of sound identification, whereas signals in an inferior frontal region predicted response time. Our findings provide neurophysiological evidence for a functional distinction between sensory and decision mechanisms underlying auditory object identification. The present results also indicate a link between inferior frontal lobe activation and response-selection processes during auditory perception tasks.

The incidence of atypical language lateralization in normal left-handed and ambidextrous subjects is higher than in normal right-handed subjects (22% vs 4-6%). These whole-brain results confirm previous findings in a left-handed cohort studied with fMRI of the lateral frontal lobe. Associations observed between personal handedness and LI and family history of handedness and LI may indicate a common genetic factor underlying the inheritance of handedness and language lateralization.

LSN analysis revealed that interconnectivity patterns of brain regions can be used to classify subjects with AD, those with aMCI, and CN subjects. In addition, the altered connectivity networks were significantly correlated with the results of cognitive tests.

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In an effort to develop MRI methods for the evaluation of tumor angiogenesis (new blood vessel formation), MRI-derived cerebral blood volume (CBV) information has been compared to histologic measures of microvessel density (MVD). Although MVD is a standard marker of angiogenesis, it is not a direct correlate of the volume measurements made with MRI, and therefore inappropriate for the development and validation of the MR techniques. Therefore, the goal of this study was to develop an approach by which MR measurements of CBV can be directly correlated. To this end, dynamic susceptibility contrast (DSC) MRI experiments were performed in six Fisher rats implanted with 9L gliosarcoma brain tumors. Subsequently, the circulation was perfused with a latex compound (Microfilா), after which 50-m tissue sections were analyzed for vessel count, diameter, and the fraction of area comprised of vessels. traditional methods are more qualitative than quantitative and do not provide sufficient information regarding tumor angiogenesis, i.e., new blood vessel formation, a process necessary for the establishment, growth, and metastasis of the tumor (1,2). It is therefore the hope that techniques which provide more specific information about tumor vascularity will improve our ability to better diagnose tumors and optimize treatment strategies. MRI methods that provide measurements of blood volume may satisfy this goal.There are two approaches generally employed for measuring blood volume using MRI. One is a method based on susceptibility (T 2 or T* 2 ) contrast (3-6) and the other on relaxivity (T 1 ) contrast (7-11). While the feasibility of both approaches has been demonstrated, along with their ability to differentiate histological tumor types (6,(12)(13)(14) and predict tumor grade (14,15), technical issues regarding the relationship between the MR signal intensity and tissue blood volume fraction remain. Unlike nuclear medicine techniques, the MR signal is not directly related to the concentration of the contrast agent in the tissue. Rather, it is a function of the ability of the contrast agent to affect water relaxation. As a consequence, the relation between MR signal intensity and blood contrast concentration, which in turn gives a measure of blood volume, is not always straightforward. For this reason the development of MRI blood volume methods requires validation.The common practice to determine whether these techniques serve as appropriate markers of angiogenesis has been to compare the blood volume results to measurements of microvessel density (MVD), the current standard for assessing the degree of angiogenesis. However, this comparison is problematic for several reasons. Since the MR measurement of blood volume depends on both vessel number (i.e., MVD) and vessel size, MVD does not provide a true independent validation of the MR methods. Furthermore, recent results demonstrate that the vessel diameter and MVD can change with tumor growth (16), with vessels becoming quite large and tortuous at later stages. Also, Maniot...