Faculty Bibliography

Voltage-sensitive dye imaging of mouse thalamocortical slices demonstrated that electrical stimulation of the centrolateral intralaminar thalamic nucleus (CL) resulted in the specific activation of thalamic reticular nucleus, striatum/putamen, and cortical layers 5, 6, and 1. By contrast, ventrobasal (VB) thalamic stimulation, while activating the reticular and basal ganglia nuclei, also activated directly layers 4 and deep 5 of the cortex. Conjoined stimulation of the VB and CL nuclei resulted in supralinear summation of the two inputs at cortical output layer 5, demonstrating coincidence detection along the apical dendrites. This supralinear summation was also noticed at gamma band stimulus frequency ( approximately 40 Hz). Direct stimulation of cortical layer 1, after a radial section of the cortex that spared only that layer, was shown to sum supralinearly with the cortical activation triggered by VB stimulation, providing a second demonstration for coincidence detection. Coincidence detection by coactivation of the specific (VB) and nonspecific (CL) thalamic nuclei has been proposed as the basis for the temporal conjunction that supports cognitive binding in the brain

Over the last four decades elegant sets of a single-cell studies, originating from various research groups, have contributed significantly to our understanding of olivary and cerebellar physiology. Nevertheless questions relating to the dynamic properties of olivocerebellar network, as a system, remain unsolved. We may be reaching the limits of what can be learned using the single-cell recordings. Further research on this subject may require study of the spatiotemporal activity profiles of ensemble neuronal activity. This paper summarizes results obtained using voltage-sensitive dye imaging in inferior olive slices, and the use of mathematical modeling to address such activity profiles

Voltage-sensitive dye imaging (VDI) of cortical activation patterns generated by electrical stimulation of thalamocortical afferents axons at different frequencies was studied, in vitro, using mouse brain slices. The study demonstrated that thalamocortical afferent axons stimulation could follow frequencies as high as 120 Hz without marked reduction. By contrast the power spectral density amplitude ratio in cortical layer 4 demonstrated a rapidly sigmoidal reduction at frequencies above 60 Hz. Similar findings were obtained with direct cortical afferent axons stimulation that obviated possible interactions at thalamic level. As pre-synaptic afferent field potentials, simultaneously recorded with the VDI at cortical level, followed higher stimulation frequency, it is concluded that cortical activity reduction is secondary to synaptic transmission failure. This interpretation agrees with the result from deep-brain stimulation (

This report identifies evidence of partially functional cerebral regions in catastrophically injured brains. To study five patients in a persistent vegetative state (PVS) with different behavioural features, we employed [(18)F]fluorodeoxyglucose-positron emission tomography (FDG-PET), MRI and magnetoencephalographic (MEG) responses to sensory stimulation. Each patient's brain expressed a unique metabolic pattern. In three of the five patients, co-registered PET/MRI correlate islands of relatively preserved brain metabolism with isolated fragments of behaviour. Two patients had suffered anoxic injuries and demonstrated marked decreases in overall cerebral metabolism to 30-40% of normal. Two other patients with non-anoxic, multifocal brain injuries demonstrated several isolated brain regions with relatively higher metabolic rates, that ranged up to 50-80% of normal. Nevertheless, their global metabolic rates remained <50% of normal. MEG recordings from three PVS patients provide clear evidence for the absence, abnormality or reduction of evoked responses. Despite major abnormalities, however, these data also provide evidence for localized residual activity at the cortical level. Each patient partially preserved restricted sensory representations, as evidenced by slow evoked magnetic fields and gamma band activity. In two patients, these activations correlate with isolated behavioural patterns and metabolic activity. Remaining active regions identified in the three PVS patients with behavioural fragments appear to consist of segregated corticothalamic networks that retain connectivity and partial functional integrity. A single patient who suffered severe injury to the tegmental mesencephalon and paramedian thalamus showed widely preserved cortical metabolism, and a global average metabolic rate of 65% of normal. The relatively high preservation of cortical metabolism in this patient defines the first functional correlate of clinical- pathological reports associating permanent unconsciousness with structural damage to these regions. The specific patterns of preserved metabolic activity identified in these patients do not appear to represent random survivals of a few neuronal islands; rather they reflect novel evidence of the modular nature of individual functional networks that underlie conscious brain function. The variations in cerebral metabolism in chronic PVS patients indicate that some cerebral regions can retain partial function in catastrophically injured brains

OBJECTIVE: To minimize the risks associated with treating cortical cerebral arteriovenous malformations (AVMs), we developed a technique combining functional imaging and cerebral angiography. The functional loci obtained by performing magnetoencephalography (MEG) are projected onto stereoscopic pairs of a stereotactically derived digital subtraction angiogram. The result is a simultaneous three-dimensional perspective of the angioarchitecture of an AVM and its relationship to the sensorimotor cortex. METHODS: Eight patients underwent multimodality brain imaging, including magnetic resonance imaging, functional mapping via MEG, and stereotactic angiography using a modified Compass fiducial system (Compass International, Rochester, MN). The coordinates derived by performing MEG were superimposed onto stereotactic, stereoscopic, angiographic pairs using custom-made distortion correction and coordinate transfer software. RESULTS: The magnetoencephalographic angiogram allowed simultaneous viewing of the angioarchitecture of the AVM nidus, the feeding vessels, and the draining veins and their relationship to the normal cerebral vasculature and functional cortex. This imaging technique was particularly valuable in identifying en passant vessels that supplied functional cortex and was used during the treatment of these lesions. CONCLUSION: The techniques of MEG and cerebral angiography were combined to provide simultaneous viewing of both modalities in a three-dimensional perspective. This technique can aid in risk stratification in the management of patients with cerebral AVMs. In addition, this technique can facilitate the selective targeting of vessels, thus potentially reducing the risks associated with embolization of these formidable lesions

We used somatosensory cortical slices from 2-5 week old rats to investigate the role of neuromodulators on the interactions between low (2 to 10Hz) and high (40 Hz) frequency cortical inputs. Slices were stained with the voltage-sensitive dye RH795 and their fluorescent activity was recorded using a CCD camera (Fujix HRDeltaron 1700). Electrical stimulation was delivered by two concentric bipolar electrodes positioned over the surface of white matter with a 1-2 mm separation.) Application of 5-20M of carbachol (a muscarinic ACh receptor agonist) facilitated both the low and high frequency-induced cortical responses. A significant increase in amplitude and duration of the responses within the deep cortical layers was observed (n=5). However, the characteristic spatial profiles generated by the low and high frequency cortical activation remained unmodified (see the accompanying abstract Urbano et al., 2002; Contreras & Llinas, 2001; J. Neuroscience). Indeed, during high frequency stimulation, the area of initial cortical excitation was laterally reduced to a small radial column. Furthermore, in the presence of carbachol a single shock applied during the 40Hz stimulation was able to further facilitate the cortical signals induced by the 40Hz train. A 50-75 % increase in the slope of the rising phase of the 40Hz train responses was observed after the single shock stimulation (n=6). These results suggest that interactions between high and low frequency cortical activity could be significantly influenced by the muscarinic cholinergic system

Serotonin release from rat caudate preterminals and abdominal mast cell was determined in vitro using three-photon autofluorescence imaging. Three photon illumination was implemented with a Millennia X femtosecond laser < 80fs Tsunami using an excitation wave length of 750nm. Pulse broadening reduction was achieved via GDV (External Group Velocity Dispersion) compensation. An AX70 Olympus microscope with an x60 infrared objective lens, a homemade scanning/detection system, and data analysis program were a part of the three-photon system. Direct inspection demonstrated that serotonin (but not dopamine nor noradrenalin) filled micro-capillaries fluoresced at 750nm. Mast Cell: Fluorescent was observed in the large mast cell vesicles in the cytosol space. Following addition of 100uM ATP to the bath fluoresce was reduced bellow one third and the cell volume increased about 20%. No reduction of left over fluorescent was observed. Caudate Nucleus: bright fluorescent dots of about 1u diameter, which matched the size of pre-synaptic terminals surronded the somata of caudate neuron. Fluorescence intensity rapidly decreased after electric stimulation of adjacent area. Clear differences were detected in the fluorescence response to activation of mast cell and caudate nucleus tissue. In the former the number of fluorescent particles changed in the latter the overall intensity changed. This is to be expected given that the size of mast cell vesicle is sufficiently large to be imaged individually while this is not the case for presynaptic vesicles. In the latter case vesicular clusters are probably being imaged