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Michael D Fox

Publications and source records attributed to Michael D Fox.

9 recordsLinked to original sources
PubMed2006

Coherent spontaneous activity identifies a hippocampal-parietal memory network.

Despite traditional theories emphasizing parietal contributions to spatial attention and sensory-motor integration, functional MRI (fMRI) experiments in normal subjects suggest that specific regions within parietal cortex may also participate in episodic memory. Here we examined correlations in spontaneous blood-oxygenation-level-dependent (BOLD) signal fluctuations in a resting state to identify the network associated with the hippocampal formation (HF) and determine whether parietal regions were elements of that network. In the absence of task, stimuli, or explicit mnemonic demands, robust correlations were observed between activity in the HF and several parietal regions (including precuneus, posterior cingulate, retrosplenial cortex, and bilateral inferior parietal lobule). These HF-correlated regions in parietal cortex were spatially distinct from those correlated with the motion-sensitive MT+ complex. Reanalysis of event-related fMRI studies of recognition memory showed that the regions spontaneously correlated with the HF (but not MT+) were also modulated during directed recollection. These regions showed greater activity to successfully recollected items as compared with other trial types. Together, these results associate specific regions of parietal cortex that are sensitive to successful recollection with the HF.

Adolescent↗
PubMed2006

Spontaneous neuronal activity distinguishes human dorsal and ventral attention systems.

On the basis of task-related imaging studies in normal human subjects, it has been suggested that two attention systems exist in the human brain: a bilateral dorsal attention system involved in top-down orienting of attention and a right-lateralized ventral attention system involved in reorienting attention in response to salient sensory stimuli. An important question is whether this functional organization emerges only in response to external attentional demands or is represented more fundamentally in the internal dynamics of brain activity. To address this question, we examine correlations in spontaneous fluctuations of the functional MRI blood oxygen level-dependent signal in the absence of task, stimuli, or explicit attentional demands. We identify a bilateral dorsal attention system and a right-lateralized ventral attention system solely on the basis of spontaneous activity. Further, we observe regions in the prefrontal cortex correlated with both systems, a potential mechanism for mediating the functional interaction between systems. These findings demonstrate that the neuroanatomical substrates of human attention persist in the absence of external events, reflected in the correlation structure of spontaneous activity.

Attention↗
PubMed2005

Coherent spontaneous activity accounts for trial-to-trial variability in human evoked brain responses.

Trial-to-trial variability in the blood oxygen level-dependent (BOLD) response of functional magnetic resonance imaging has been shown to be relevant to human perception and behavior, but the sources of this variability remain unknown. We demonstrate that coherent spontaneous fluctuations in human brain activity account for a significant fraction of the variability in measured event-related BOLD responses and that spontaneous and task-related activity are linearly superimposed in the human brain.

Brain↗
PubMed2005

Transient BOLD responses at block transitions.

Block-design fMRI responses include sustained components present for the duration of each task block as well as transient components at the beginning and end of each block. Almost all prior block-design fMRI studies have focused on the sustained response components while the transient responses at block transitions have been largely ignored. These transients, therefore, remain poorly characterized. We here present a systematic study of block-transition transient responses obtained using four widely divergent tasks. We characterize transient response topography and examine the extent to which these responses vary across different tasks and between block onset and offset. Our analysis reveals that certain regions show transient responses regardless of task or transition type. However, our analysis also shows that specific task state transitions give rise to transient responses with unique spatial profiles. Relevance of the current findings to studies of exogenous attention, task shifting, and the BOLD overshoot is discussed.

Adult↗
PubMed2005

The human brain is intrinsically organized into dynamic, anticorrelated functional networks.

During performance of attention-demanding cognitive tasks, certain regions of the brain routinely increase activity, whereas others routinely decrease activity. In this study, we investigate the extent to which this task-related dichotomy is represented intrinsically in the resting human brain through examination of spontaneous fluctuations in the functional MRI blood oxygen level-dependent signal. We identify two diametrically opposed, widely distributed brain networks on the basis of both spontaneous correlations within each network and anticorrelations between networks. One network consists of regions routinely exhibiting task-related activations and the other of regions routinely exhibiting task-related deactivations. This intrinsic organization, featuring the presence of anticorrelated networks in the absence of overt task performance, provides a critical context in which to understand brain function. We suggest that both task-driven neuronal responses and behavior are reflections of this dynamic, ongoing, functional organization of the brain.

Attention↗
PubMed2005

The BOLD onset transient: identification of novel functional differences in schizophrenia.

Blood oxygen level dependent (BOLD) signals characteristically exhibit an overshoot (transient signal increase) at the beginning of fMRI task blocks. This onset transient has often been overlooked as an independent measure of neuronal activity, but it may represent unique functional processes. We examined onset transient responses in normal subjects and individuals with schizophrenia performing three cognitive tasks. These analyses revealed a regionally specific and task specific attenuation of the onset transient in individuals with schizophrenia during performance of a working memory task. Furthermore, this attenuation was often not accompanied by a corresponding population difference in the sustained response, and is missed through conventional fMRI analysis techniques. Relevance of these findings to both an interpretation of the onset transient and the pathology of schizophrenia are discussed.

Adult↗
PubMed2004

Favre-Racouchot disease.

Solar elastosis with comedones studding the central face is often referred to as Favre-Racouchot disease. These open and cystically dilated comedones tend to appear in the periorbital region of the face. The clinical manifestations, pathogenesis and current treatment of this disorder are reviewed.

Facial Dermatoses↗
PubMed2003

Clinical characteristics of patients with an abnormal clomiphene citrate challenge test.

OBJECTIVE: The study was undertaken to identify the clinical characteristics associated with an abnormal clomiphene citrate challenge (CC) test. STUDY DESIGN: The medical records of 123 women seen in a referral-based infertility practice who had a CC test as part of their infertility workup were reviewed. Eighty-five patients had a normal CC test and 38 patients had an abnormal test. Demographic, clinical, and laboratory characteristics were reviewed and analyzed. RESULTS: Women with abnormal CC tests were significantly older, had a lower mean body mass index, family history of early menopause, and shorter cycle intervals. Patients with an abnormal CC test had a pregnancy rate significantly lower than other women in this case series. CONCLUSION: Increased age, lower body mass index, shorter cycle intervals, lower cycle day 21 progesterone levels, and decreased pregnancy rates are associated with an abnormal CC test. Women with an abnormal CC test also tended to have a familial history of early menopause.

Adult↗