Imagined rotations of self versus objects: an fMRI study
Wraga M, Shephard JM, Church JA, Inati S and Kosslyn SM Neuropsychologia 43(9):1351-61 (2005)
This study used functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying two types of spatial transformations: imagined object rotations and imagined rotations of the self about an object. Participants viewed depictions of single three-dimensional Shepard--Metzler objects situated within a sphere. A T-shaped prompt appeared outside of the sphere at different locations across trials. In the object rotation task, participants imagined rotating the object so that one of its ends was aligned with the prompt. They then judged whether a textured portion of the object would be visible in its new orientation. In the self rotation task, they imagined rotating themselves to the location of the T-prompt, and then judged whether a textured portion of the object would be visible from the new viewpoint. Activation in both tasks was compared to respective control conditions in which identical judgments were made without rotation. A direct comparison of self and object rotation tasks revealed activation spreading from left premotor to left primary motor (M1) cortex (areas 6/4) for imagined object rotations, but not imagined self rotations. In contrast, the self rotation task activated left supplementary motor area (SMA; area 6). In both transformations, activation also occurred in other regions. These findings provide evidence for multiple spatial-transformation mechanisms within the human cognitive system.
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Experiments on random packings of ellipsoids
Man W, Donev A, Stillinger FH, Sullivan MT, Russel WB, Heeger D, Inati S, Torquato S and Chaikin PM Phys Rev Lett 94(19):198001 (2005)
Recent simulations indicate that ellipsoids can pack randomly more densely than spheres and, remarkably, for axes ratios near 1.25:1:0.8 can approach the densest crystal packing (fcc) of spheres, with a packing fraction of 74%. We demonstrate that such dense packings are realizable. We introduce a novel way of determining packing density for a finite sample that minimizes surface effects. We have fabricated ellipsoids and show that, in a sphere, the radial packing fraction phi(r) can be obtained from V(h), the volume of added fluid to fill the sphere to height h. We also obtain phi(r) from a magnetic resonance imaging scan. The measurements of the overall density phi(avr), phi(r) and the core density phi(0) = 0.74 +/- 0.005 agree with simulations.
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Functional connectivity: integrating behavioral, diffusion tensor imaging, and functional magnetic resonance imaging data sets
Baird AA, Colvin MK, Vanhorn JD, Inati S and Gazzaniga MS J Cogn Neurosci 17(4):687-93 (2005)
In the present study, we combined 2 types of magnetic resonance technology to explore individual differences on a task that required the recognition of objects presented from unusual viewpoints. This task was chosen based on previous work that has established the necessity of information transfer from the right parietal cortex to the left inferior cortex for its successful completion. We used reaction times (RTs) to localize regions of cortical activity in the superior parietal and inferior frontal regions (blood oxygen level-dependent [BOLD] response) that were more active with longer response times. These regions were then sampled, and their signal change used to predict individual differences in structural integrity of white matter in the corpus callosum (using diffusion tensor imaging). Results show that shorter RTs (and associated increases in BOLD response) are associated with increased organization in the splenium of the corpus callosum, whereas longer RTs are associated with increased organization in the genu.
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An fMRI study of reward-related probability learning
Delgado MR, Miller MM, Inati S and Phelps EA Neuroimage 24(3):862-73 (2005)
The human striatum has been implicated in processing reward-related information. More recently, activity in the striatum, particularly the caudate nucleus, has been observed when a contingency between behavior and reward exists, suggesting a role for the caudate in reinforcement-based learning. Using a gambling paradigm, in which affective feedback (reward and punishment) followed simple, random guesses on a trial by trial basis, we sought to investigate the role of the caudate nucleus as reward-related learning progressed. Participants were instructed to make a guess regarding the value of a presented card (if the value of the card was higher or lower than 5). They were told that five different cues would be presented prior to making a guess, and that each cue indicated the probability that the card would be high or low. The goal was to learn the contingencies and maximize the reward attained. Accuracy, as measured by participant's choices, improved throughout the experiment for cues that strongly predicted reward, while no change was observed for unpredictable cues. Event-related fMRI revealed that activity in the caudate nucleus was more robust during the early phases of learning, irrespective of contingencies, suggesting involvement of this region during the initial stages of trial and error learning. Further, the reward feedback signal in the caudate nucleus for well-learned cues decreased as learning progressed, suggesting an evolving adaptation of reward feedback expectancy as a behavior-outcome contingency becomes more predictable.
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Actions or hand-object interactions? Human inferior frontal cortex and action observation
Johnson-Frey SH, Maloof FR, Newman-Norlund R, Farrer C, Inati S and Grafton ST Neuron 39(6):1053-8 (2003)
Cells in macaque ventral premotor cortex (area F5c) respond to observation or production of specific hand-object interactions. Studies in humans associate the left inferior frontal gyrus, including putative F5 homolog pars opercularis, with observing hand actions. Are these responses related to the realized goal of a prehensile action or to the observation of dynamic hand movements? Rapid, event-related fMRI was used to address this question. Subjects watched static pictures of the same objects being grasped or touched while performing a 1-back orienting task. In all 17 subjects, bilateral inferior frontal cortex was differentially activated in response to realized goals of observed prehensile actions. Bilaterally, precentral gyrus was most frequently activated (82%) followed by pars triangularis (73%) and pars opercularis (65%).
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Finding the self? An event-related fMRI study
Kelley WM, Macrae CN, Wyland CL, Caglar S, Inati S and Heatherton TF J Cogn Neurosci 14(5):785-94 (2002)
Researchers have long debated whether knowledge about the self is unique in terms of its functional anatomic representation within the human brain. In the context of memory function, knowledge about the self is typically remembered better than other types of semantic information. But why does this memorial effect emerge? Extending previous research on this topic (see Craik et al., 1999), the present study used event-related functional magnetic resonance imaging to investigate potential neural substrates of self-referential processing. Participants were imaged while making judgments about trait adjectives under three experimental conditions (self-relevance, other-relevance, or case judgment). Relevance judgments, when compared to case judgments, were accompanied by activation of the left inferior frontal cortex and the anterior cingulate. A separate region of the medial prefrontal cortex was selectively engaged during self-referential processing. Collectively, these findings suggest that self-referential processing is functionally dissociable from other forms of semantic processing within the human brain.
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Extensive individual differences in brain activations associated with episodic retrieval are reliable over time
Miller MB, Van Horn JD, Wolford GL, Handy TC, Valsangkar-Smyth M, Inati S, Grafton S and Gazzaniga MS J Cogn Neurosci 14(8):1200-14 (2002)
The localization of brain functions using neuroimaging techniques is commonly dependent on statistical analyses of groups of subjects in order to identify sites of activation, particularly in studies of episodic memory. Exclusive reliance on group analysis may be to the detriment of understanding the true underlying cognitive nature of brain activations. In the present study, we found that the patterns of brain activity associated with episodic retrieval are very distinct for individual subjects from the patterns of brain activity at the group level. These differences go beyond the relatively small variations due to cyctoarchitectonic differences or spatial normalization. We quantify this individual variability by cross-correlating volumes of brain images. We demonstrate that individual patterns of brain activity are reliable over time despite their extensive variability. We suggest that varied but reliable individual patterns of significant brain activity may be indicative of different cognitive strategies used to produce a recognition response. We believe that individual analysis in conjunction with group analysis may be critical to fully understanding the relationship between retrieval processes and underlying brain regions.
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MRI assessment of spared fibers following callosotomy: a second look
Corballis PM, Inati S, Funnell MG, Grafton ST and Gazzaniga MS Neurology 57(7):1345-6 (2001)
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Brain activations associated with shifts in response criterion on a recognition test
Miller MB, Handy TC, Cutler J, Inati S and Wolford GL Can J Exp Psychol 55(2):162-73 (2001)
Sensitivity and bias can be manipulated independently on a recognition test. The goal of this fMRI study was to determine whether neural activations associated with manipulations of a decision criterion would be anatomically distinct from neural activations associated with manipulations of memory strength and episodic retrieval. The results indicated that activations associated with shifting criteria (a manipulation of bias) were located in bilateral regions of the lateral cerebellum, lateral parietal lobe, and the dorsolateral prefrontal cortex extending from the supplementary motor area. These regions were anatomically distinct from activations in the prefrontal cortex produced during memory-based retrieval processes (manipulations of sensitivity), which tended to be more medial and anterior. These later activations are consistent with previous studies of episodic retrieval. Determining patterns of neural activations associated with decision-making processes relative to memory processes has important implications for Cognitive Neuroscience, including the use of these patterns to compare memory models in different paradigms.
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Eye position influences auditory responses in primate inferior colliculus
Groh JM, Trause AS, Underhill AM, Clark KR and Inati S Neuron 29(2):509-18 (2001)
We examined the frame of reference of auditory responses in the inferior colliculus in monkeys fixating visual stimuli at different locations. Eye position modulated the level of auditory responses in 33% of the neurons we encountered, but it did not appear to shift their spatial tuning. The effect of eye position on auditory responses was substantial-comparable in magnitude to that of sound location. The eye position signal appeared to interact with the auditory responses in at least a partly multiplicative fashion. We conclude that the representation of sound location in primate IC is distributed and that the frame of reference is intermediate between head- and eye-centered coordinates. The information contained in these neurons appears to be sufficient for later neural stages to calculate the positions of sounds with respect to the eyes.
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Pulsed electron-nuclear double resonance (ENDOR) at 140 GHz
Bennati M, Farrar CT, Bryant JA, Inati SJ, Weis V, Gerfen GJ, Riggs-Gelasco P, Stubbe J and Griffin RG J Magn Reson 138(2):232-43 (1999)
We describe a spectrometer for pulsed ENDOR at 140 GHz, which is based on microwave IMPATT diode amplifiers and a probe consisting of a TE011 cavity with a high-quality resonance circuit for variable radiofrequency irradiation. For pulsed EPR we obtain an absolute sensitivity of 3x10(9) spins/Gauss at 20 K. The performance of the spectrometer is demonstrated with pulsed ENDOR spectra of a standard bis-diphenylene-phenyl-allyl (BDPA) doped into polystyrene and of the tyrosyl radical from E. coli ribonucleotide reductase (RNR). The EPR spectrum of the RNR tyrosyl radical displays substantial g-anisotropy at 5 T and is used to demonstrate orientation-selective Davies-ENDOR.
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Polarization-enhanced NMR spectroscopy of biomolecules in frozen solution
Hall DA, Maus DC, Gerfen GJ, Inati SJ, Becerra LR, Dahlquist FW and Griffin RG Science 276(5314):930-2 (1997)
Large dynamic nuclear polarization signal enhancements (up to a factor of 100) were obtained in the solid-state magic-angle spinning nuclear magnetic resonance (NMR) spectra of arginine and the protein T4 lysozyme in frozen glycerol-water solutions with the use of dynamic nuclear polarization. Polarization was transferred from the unpaired electrons of nitroxide free radicals to nuclear spins through microwave irradiation near the electron paramagnetic resonance frequency. This approach may be a generally applicable signal enhancement scheme for the high-resolution solid-state NMR spectroscopy of biomolecules.
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Spin correlations and symmetrization in the nuclear magnetic resonances of molecular systems with tunneling
Inati SJ and Zilm KW Phys Rev Lett 68(22):3273-6 (1992)
Spin correlation effects are often observed in inelastic neutron scattering and nuclear magnetic resonance (NMR) when tunneling is important. In studies of proton-proton exchange couplings observed in the 1H NMR of transition-metal polyhydrides, we have had to deal with exchange degeneracies in large collections of identical spins. This Letter presents a method that easily handles such problems with low symmetry, eliminates ad hoc assumptions with respect to the feasibility of any particular permutation of particles, and is readily implemented in computer calculations.
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