Bradley R. Buchsbaum

Meta-analysis of neuroimaging studies of the Wisconsin Card-Sorting task and component processes

A quantitative meta‐analysis using the activation likelihood estimation (ALE) method was used to investigate the brain basis of the Wisconsin Card‐Sorting Task (WCST) and two hypothesized component processes, task switching and response suppression. All three meta‐analyses revealed distributed frontoparietal activation patterns consistent with the status of the WCST as an attention‐demanding executive task. The WCST was associated with extensive bilateral clusters of reliable cross‐study activity in the lateral prefrontal cortex, anterior cingulate cortex, and inferior parietal lobule. Task switching revealed a similar, although less robust, frontoparietal pattern with additional clusters of activity in the opercular region of the ventral prefrontal cortex, bilaterally. Response‐suppression tasks, represented by studies of the go/no‐go paradigm, showed a large and highly right‐lateralized region of activity in the right prefrontal cortex. The activation patterns are interpreted as reflecting a neural fractionation of the cognitive components that must be integrated during the performance of the WCST. Hum Brain Mapp 25:35–45, 2005.

Conduction aphasia, sensory-motor integration, and phonological short-term memory - An aggregate analysis of lesion and fMRI data

Conduction aphasia is a language disorder characterized by frequent speech errors, impaired verbatim repetition, a deficit in phonological short-term memory, and naming difficulties in the presence of otherwise fluent and grammatical speech output. While traditional models of conduction aphasia have typically implicated white matter pathways, recent advances in lesions reconstruction methodology applied to groups of patients have implicated left temporoparietal zones. Parallel work using functional magnetic resonance imaging (fMRI) has pinpointed a region in the posterior most portion of the left planum temporale, area Spt, which is critical for phonological working memory. Here we show that the region of maximal lesion overlap in a sample of 14 patients with conduction aphasia perfectly circumscribes area Spt, as defined in an aggregate fMRI analysis of 105 subjects performing a phonological working memory task. We provide a review of the evidence supporting the idea that Spt is an interface site for the integration of sensory and vocal tract-related motor representations of complex sound sequences, such as speech and music and show how the symptoms of conduction aphasia can be explained by damage to this system.

Role of anterior temporal cortex in auditory sentence comprehension: an fMRI study.

Recent neuropsychological and functional imaging evidence has suggested a role for anterior temporal cortex in sentence-level comprehension. We explored this hypothesis using event-related fMRI. Subjects were scanned while they listened to either a sequence of environmental sounds describing an event or a corresponding sentence matched as closely as possible in meaning. Both types of stimuli required subjects to integrate auditory information over time to derive a similar meaning, but differ in the processing mechanisms leading to the integration of that information, with speech input requiring syntactic mechanisms and environmental sounds utilizing non-linguistic mechanisms. Consistent with recent claims, sentences produced greater activation than environmental sounds in anterior superior temporal lobe bilaterally. A similar speech > sound activation pattern was noted also in posterior superior temporal regions in the left. Envirornmental sounds produced greater activation than sentences in right inferior frontal gyrus. The results provide support for the view that anterior temporal cortex plays an important role in sentence-level comprehension.

Diffusion tensor imaging in schizophrenia.

BACKGROUND Alignment of white matter axons as inferred from diffusion tensor imaging has indicated changes in schizophrenia in frontal and frontotemporal white matter. METHODS Diffusion tensor anisotropy and anatomical magnetic resonance images were acquired in 64 patients with schizophrenia and 55 normal volunteers. Anatomical images were acquired with a magnetization prepared rapid gradient echo sequence, and diffusion tensor images used a pulsed gradient spin-echo acquisition. Images were aligned and warped to a standard brain, and anisotropy in normal volunteers and patients was compared using significance probability mapping. RESULTS Patients showed widespread areas of reduced anisotropy, including the frontal white matter, the corpus callosum, and the frontal longitudinal fasciculus. CONCLUSIONS These findings, which are consistent with earlier reports of frontal decreases in anisotropy, demonstrate that the effects are most prominent in frontal and callosal areas and are particularly widespread in frontal white matter regions.

Deformation-based morphometry and its relation to conventional volumetry of brain lateral ventricles in MRI.

Deformation-based morphometry (DBM) is a useful technique to detect morphological differences over the entire brain since it analyses positional differences between every voxel and a standard brain. In this report we compare DBM to semimanual tracing of brain ventricles in a population of 39 patients with schizophrenia. High-resolution T(1)-weighted magnetic resonance images were obtained and processed with DBM and interactive tracing software. We evaluate the validity of the DBM in two different approaches. First, we divide subjects into two groups based on the mean ventricular/brain ratios and compute statistical maps of displacement vectors and their spatial derivatives. This analysis demonstrates a striking consistency of the DBM and visual tracing results. We show that restricting the information about the deformation fields by computing the local Jacobian determinant (as a measure of volume change) provides evidence of the shape of ventricular deformation which is unavailable from ventricular volume measures alone. Second, we compute a mean measure of the Jacobian values over the entire ventricles and observe a correlation of r = 0.962 with visual tracing based ventricular/brain ratios. The results support the usefulness and validity of DBM for the local and global examination of brain morphology.

Noise differentially impacts phoneme representations in the auditory and speech motor systems

Significance Contentious debate remains regarding the role of the redundant motor activation during speech perception. In this functional MRI study, multivariate pattern analysis revealed stronger multivoxel phoneme discrimination in speech motor regions than auditory cortices when the speech phonemes were moderately degraded by noise. Our findings provide neuroimaging evidence for the sensorimotor integration account. Preserved phoneme discrimination in speech motor areas may compensate for loss of specificity in noise-impoverished speech representations, which aids speech perception under adverse listening conditions. Although it is well accepted that the speech motor system (SMS) is activated during speech perception, the functional role of this activation remains unclear. Here we test the hypothesis that the redundant motor activation contributes to categorical speech perception under adverse listening conditions. In this functional magnetic resonance imaging study, participants identified one of four phoneme tokens (/ba/, /ma/, /da/, or /ta/) under one of six signal-to-noise ratio (SNR) levels (–12, –9, –6, –2, 8 dB, and no noise). Univariate and multivariate pattern analyses were used to determine the role of the SMS during perception of noise-impoverished phonemes. Results revealed a negative correlation between neural activity and perceptual accuracy in the left ventral premotor cortex and Broca’s area. More importantly, multivoxel patterns of activity in the left ventral premotor cortex and Broca’s area exhibited effective phoneme categorization when SNR ≥ –6 dB. This is in sharp contrast with phoneme discriminability in bilateral auditory cortices and sensorimotor interface areas (e.g., left posterior superior temporal gyrus), which was reliable only when the noise was extremely weak (SNR > 8 dB). Our findings provide strong neuroimaging evidence for a greater robustness of the SMS than auditory regions for categorical speech perception in noise. Under adverse listening conditions, better discriminative activity in the SMS may compensate for loss of specificity in the auditory system via sensorimotor integration.

Reading, hearing, and the planum temporale

Many neuroimaging studies of single-word reading have been carried out over the last 15 years, and a consensus as to the brain regions relevant to this task has emerged. Surprisingly, the planum temporale (PT) does not appear among the catalog of consistently active regions in these investigations. Recently, however, several studies have offered evidence suggesting that the left posteromedial PT plays a role in both speech production and speech perception. It is not clear, then, why so many neuroimaging studies of single-word reading--a task requiring speech production--have tended not to find evidence of PT involvement. In the present work, we employed a high-powered rapid event-related fMRI paradigm involving both single pseudoword reading and single pseudoword listening to assess activity related to reading and speech perception in the PT as a function of the degree of spatial smoothing applied to the functional images. We show that the speech area of the PT [Sylvian-parietal-temporal (Spt)] is best identified when only a moderate (5 mm) amount of spatial smoothing is applied to the data before statistical analysis. Moreover, increasing the smoothing window to 10 mm obliterates activation in the PT, suggesting that failure to find PT activation in past studies may relate to this factor.

Repetition Suppression and Reactivation in Auditory–Verbal Short-Term Recognition Memory

The neural response to stimulus repetition is not uniform across brain regions, stimulus modalities, or task contexts. For instance, it has been observed in many functional magnetic resonance imaging (fMRI) studies that sometimes stimulus repetition leads to a relative reduction in neural activity (repetition suppression), whereas in other cases repetition results in a relative increase in activity (repetition enhancement). In the present study, we hypothesized that in the context of a verbal short-term recognition memory task, repetition-related “increases” should be observed in the same posterior temporal regions that have been previously associated with “persistent activity” in working memory rehearsal paradigms. We used fMRI and a continuous recognition memory paradigm with short lags to examine repetition effects in the posterior and anterior regions of the superior temporal cortex. Results showed that, consistent with our hypothesis, the 2 posterior temporal regions consistently associated with working memory maintenance, also show repetition increases during short-term recognition memory. In contrast, a region in the anterior superior temporal lobe showed repetition suppression effects, consistent with previous research work on perceptual adaptation in the auditory–verbal domain. We interpret these results in light of recent theories of the functional specialization along the anterior and posterior axes of the superior temporal lobe.

Neural Representations of Relevant and Irrelevant Features in Perceptual Decision Making

Although perceptual decision making activates a network of brain areas involved in sensory, integrative, and motor functions, circuit activity can clearly be modulated by factors beyond the stimulus. Of particular interest is to understand how the network is modulated by top-down factors such as attention. Here, we demonstrate in a motion coherence task that selective attention produces marked changes in the blood oxygen level-dependent (BOLD) response in a subset of regions within a human perceptual decision-making circuit. Specifically, when motion is attended, the BOLD response decreases with increasing motion coherence in many regions, including the motion-sensitive area MT+, the intraparietal sulcus, and the inferior frontal sulcus. However, when motion is ignored, the negative parametric response in a subset of this circuit becomes positive. Through both modeling and connectivity analyses, we demonstrate that this inversion both reflects a top-down influence and segregates attentional from accumulation regions, thereby permitting us to further delineate the contributions of different regions to the perceptual decision.

The neural basis of vivid memory is patterned on perception

When we have a rich and vivid memory for a past experience, it often feels like we are transported back in time to witness once again this event. Indeed, a perfect memory would exactly mimic the experiential quality of direct sensory perception. We used fMRI and multivoxel pattern analysis to map and quantify the similarity between patterns of activation evoked by direct perception of a diverse set of short video clips and the vivid remembering, with closed eyes, of these clips. We found that the patterns of distributed brain activation during vivid memory mimicked the patterns evoked during sensory perception. Using whole-brain patterns of activation evoked by perception of the videos, we were able to accurately classify brain patterns that were elicited when participants tried to vividly recall those same videos. A discriminant analysis of the activation patterns associated with each video revealed a high degree (explaining over 80% of the variance) of shared representational similarity between perception and memory. These results show that complex, multifeatured memory involves a partial reinstatement of the whole pattern of brain activity that is evoked during initial perception of the stimulus.