Journal Club

Direct Magnetic Source fMRI

Abstract:

Current fMRI techniques use the brain's blood oxygenation level dependent (BOLD) response to detect areas of activation during task execution. The inherent constraints of this technique are (1) significant temporal lag between the activity and the BOLD response, and (2) detection of larger and blurrier areas than where the actual neural activation occurs. The BOLD effect spreads over a large brain area, and the BOLD MR signal change is predominantly detected in the blood vessels, and loci in the close proximity of the neural activation. It has been demonstrated that neural activity induces electric currents in the cortex which produce magnetic fields that may be detectable by MR equipment. Imaging the activated areas of the brain directly during activity at the precise time when such activity occurs would allow precise localization of the neural activation both spatially and temporally.
We recorded MRI data where subjects were asked to respond to randomized auditory stimuli by squeezing an air-filled pillow. The stimuli were organized in blocks to allow traditional BOLD analysis. The BOLD analysis showed significant auditory cortex, and motor cortex activity. In order to find the activation at the neural level, we first realigned the slices to the motor movement profile, and then looked at the time evolution of the MR signal in voxels that showed strong activation with traditional BOLD analysis.

We are investigating what information the listeners use to follow meter. If they are following multiple levels of
meter simultaneously. And how well subjects follow a changing tempo inpieces of music. (an expressive performance and a mechanical were used).

State variable feedback control and Libet’s control problem

Abstract

In 1966, Benjamin Libet’s experiments showed that preparation to move a
finger, evidenced by readiness potentials, precedes conscious awareness of
the intention to move by 300 – 500 milliseconds. This result, replicated
by others, that the brain prepares a movement before a subject is aware of
the intention to move, has created controversy by casting doubt on the
widely held belief that we control our actions (free will). It has been
suggested by Libet and others that conscious control of movement may be
limited to inhibiting actions (free won’t instead of free will).
Philosophical issues aside, Libet’s results can be recast as a state
variable feedback control problem herein called Libet’s control problem:
is the system of neural signals associated with conscious intention and
movement controllable in a state variable sense? In proposing that the
Libet Control Problem is isomorphic to the state variable feedback control
problem, it is shown that state variable concepts of controllability,
observability, and the Kalman decomposition provide new insights into
Libet’s results, conscious control, and the application of state variable
feedback control in neuroscience.(Related paer in pdf)

Jan 28	Dr. Phil Fink William H. Warren Jr., Bruce A. Kay, Wendy D. Zosh, Andrew P. Duchon & Stephanie Sahuc (2001) Optic flow is used to control human walking Nature Neuroscience 4(2) Abstract: How is human locomotion visually controlled? Fifty years ago, it was proposed that we steer to a goal using optic flow, the pattern of motion at the eye that specifies the direction of locomotion. However, we might also simply walk in the perceived direction of a goal. These two hypotheses normally predict the same behavior, but we tested them in an immersive virtual environment by displacing the optic flow from the direction of walking, violating the laws of optics. We found that people walked in the visual direction of a lone target, but increasingly relied on optic flow as it was added to the display. The visual control law for steering toward a goal is a linear combination of these two variables weighted by the magnitude of flow, thereby allowing humans to have robust locomotor control under varying environmental conditions. (paper in pdf)
Feb 4	Arpan Banerjee Victor M. Eguiluz, Dante R. Chialvo, Guillermo A. Cecchi, Marwan Baliki, A. Vania Apkarian (2005) Scale free brain functional networks Physical Review Letters 94 (018102) Abstract Functionalmagnetic resonance imaging is used to extract functional networks connectingcorrelated human brain sites. Analysis of the resulting networks indifferent tasks shows that (a) the distribution of functional connections, andthe probability of finding a link versus distance are bothscale-free, (b) the characteristic path length is small and comparable withthose of equivalent random networks, and (c) the clustering coefficient isorders of magnitude larger than those of equivalent random networks.All these properties, typical of scale-free small-world networks, reflect importantfunctional information about brain states. (paper in pdf)
Feb 11	JOURNAL CLUB CANCELLED ********************************************************
Feb 18	Balazs Szemes Direct Magnetic Source fMRI Abstract: Current fMRI techniques use the brain's blood oxygenation level dependent (BOLD) response to detect areas of activation during task execution. The inherent constraints of this technique are (1) significant temporal lag between the activity and the BOLD response, and (2) detection of larger and blurrier areas than where the actual neural activation occurs. The BOLD effect spreads over a large brain area, and the BOLD MR signal change is predominantly detected in the blood vessels, and loci in the close proximity of the neural activation. It has been demonstrated that neural activity induces electric currents in the cortex which produce magnetic fields that may be detectable by MR equipment. Imaging the activated areas of the brain directly during activity at the precise time when such activity occurs would allow precise localization of the neural activation both spatially and temporally. We recorded MRI data where subjects were asked to respond to randomized auditory stimuli by squeezing an air-filled pillow. The stimuli were organized in blocks to allow traditional BOLD analysis. The BOLD analysis showed significant auditory cortex, and motor cortex activity. In order to find the activation at the neural level, we first realigned the slices to the motor movement profile, and then looked at the time evolution of the MR signal in voxels that showed strong activation with traditional BOLD analysis.
Feb 25	JOURNAL CLUB CANCELLED ********************************************************
Mar 04	Summer Rankin S. Rankin, E. Large, P. Fink, S. Houlton Following changes in tempo Abstract We are investigating what information the listeners use to follow meter. If they are following multiple levels of meter simultaneously. And how well subjects follow a changing tempo inpieces of music. (an expressive performance and a mechanical were used).
Mar 17	Dr. Emanuelle Tognoli DICKÈS Paul La psychométrie Psychometry is often assimilated to the study of tests, whenever it deals with the entirety of theories and methods of measurement in Psychology. Theoretically speaking, this book intends to clarify the purpose and impact of the measurement process in psychology.On a pratical ground, it presents an integrated view on the steps accompanying the process of measurement from the collection of observations to the results, through the application of measurement model.
Mar 25	Carey Witkov State variable feedback control and Libet’s control problem Abstract In 1966, Benjamin Libet’s experiments showed that preparation to move a finger, evidenced by readiness potentials, precedes conscious awareness of the intention to move by 300 – 500 milliseconds. This result, replicated by others, that the brain prepares a movement before a subject is aware of the intention to move, has created controversy by casting doubt on the widely held belief that we control our actions (free will). It has been suggested by Libet and others that conscious control of movement may be limited to inhibiting actions (free won’t instead of free will). Philosophical issues aside, Libet’s results can be recast as a state variable feedback control problem herein called Libet’s control problem: is the system of neural signals associated with conscious intention and movement controllable in a state variable sense? In proposing that the Libet Control Problem is isomorphic to the state variable feedback control problem, it is shown that state variable concepts of controllability, observability, and the Kalman decomposition provide new insights into Libet’s results, conscious control, and the application of state variable feedback control in neuroscience.(Related paer in pdf)
April 1	Debbie's defense
April 8	Craig Richter Top-down anticipatory modulation of low-level visual cortical activity by both dorsal and ventral visual processing systems Abstract: In recent years (Engel et al., 2001), there has been growing awareness that cortical visuomotor function is not simply a unidirectional feedforward process, but integrally involves top-down neural control, particularly during selective attention where relevant visual information must be effectively separated from irrelevant visual input. Recent studies (Fries et al., 2001; Steinmetz et al., 2000), have suggested that top-down control of sensory processing may involve modulation of the synaptic gain of sensory neurons carrying information about attended stimuli, thus amplifying the effect of this information at successive stages of sensorimotor processing. Since top-down modulation of sensory processing has been proposed to occur within task-specific coherent oscillatory networks, the selective top-down imposition of such a “bias signal” may be manifested by changes in coherence in selected task-specific pathways. The current study used local field potentials (LFPs) to demonstrate the existence of such coherent oscillatory networks in the cerebral cortex of a macaque monkey performing a go/no-go visual discrimination task. These networks were found to be coherent in the beta frequency range and to be distributed across the occipital, parietal, and temporal lobes. One network, coherent at a higher beta frequency, showed signs of top-down control from the inferior parietal cortex to lower-order visual cortical areas. This network appeared to be linked to another network recently established (Brovelli et al., 2004) in the sensorimotor system, and thus may be intimately involved in the coordination of visuomotor processing. Another network, coherent at a lower beta frequency, showed evidence of top-down control of the same lower-order visual areas by the inferior temporal cortex. These results suggest that multiple distinct top-down modulatory pathways may operate concurrently to control different aspects of visual processing. References: Brovelli A, Ding M, Ledberg A, Chen Y, Nakamura R, Bressler SL. Beta oscillations in a large-scale sensorimotor cortical network: directional influences revealed by Granger causality. Proc Natl Acad Sci U S A. 2004 Jun 29;101(26):9849-54. Epub 2004 Jun 21. Engel AK, Fries P, Singer W. Dynamic predictions: oscillations and synchrony in top-down processing. Nat Rev Neurosci. 2001 Oct;2(10):704-16. Review. Fries P, Reynolds JH, Rorie AE, Desimone R. Modulation of oscillatory neuronal synchronization by selective visual attention. Science. 2001 Feb 23;291(5508):1560-3. Steinmetz PN, Roy A, Fitzgerald PJ, Hsiao SS, Johnson KO, Niebur E. Attention modulates synchronized neuronal firing in primate somatosensory cortex. Nature. 2000 Mar 9;404(6774):187-90.
April 15	Brain Connectivity 2005
April 22	Dr. Sreenivasan Rajamoni Varela F, Lachaux JP, Rodriguez E, Martinerie J. , Nature Review Neuroscience. 2001 Apr;2(4):229-39 The brainweb: phase synchronization and large-scale integration. Abstract: The emergence of a unified cognitive moment relies on the coordination of scattered mosaics of functionally specialized brain regions. Here we review the mechanisms of large-scale integration that counterbalance the distributed anatomical and functional organization of brain activity to enable the emergence of coherent behaviour and cognition. Although the mechanisms involved in large-scale integration are still largely unknown, we argue that the most plausible candidate is the formation of dynamic links mediated by synchrony over multiple frequency bands.(paper in pdf )