Summer Papers Jan-July, 2014

"Motor cortical control of movement speed with implications for brain-machine interface control"
Journal of Neurophysiology, 112:411-429

Mouse over here for a brief summary or click to open article in a new tab.We analyzed the extent to which movement-related information could be extracted from single-trial motor cortical activity recorded while monkeys performed center-out reaching, and found that single units carry relatively little speed-related information compared with direction-related information. This result is not mitigated at the population level: simultaneously recorded population activity predicted speed with significantly lower accuracy relative to direction predictions. These results inspired the design of a new brain-machine interface (BMI) decoding algorithm called the speed-dampening Kalman filter (SDKF) that automatically slows the cursor upon detecting changes in decoded movement direction. SDKF improved success rates by a factor of 1.7 relative to a standard Kalman filter in a closed-loop BMI task requiring stable stops at targets.

"The precise temporal pattern of prehearing spontaneous activity is necessary for tonotopic map refinement."
Neuron, 82:822

Mouse over here for a brief summary or click to open article in a new tab.We provide teh first evidence that the precise temporal pattern of spontaneous activity in the auditory system plays a critical role in the establishment of a precise tonotopic organization of a central auditory pathway.

"Clinical imaging in regenerative medicine"
Nature Biotechnology, 32:804-818

Mouse over here for a brief summary or click to open article in a new tab.In regenerative medicine, clinical imaging is indispensable for characterizing damaged tissue and for measuring the safety and efficacy of therapy. However, the ability to track the fate and function of transplanted cells with current technologies is limited. Exogenous contrast labels such as nanoparticles give a strong signal in the short term but are unreliable long term. Genetically encoded labels are good both short- and long-term in animals, but in the human setting they raise regulatory issues related to the safety of genomic integration and potential immunogenicity of reporter proteins. Imaging studies in brain, heart and islets share a common set of challenges, including developing novel labeling approaches to improve detection thresholds and early delineation of toxicity and function. Key areas for future research include addressing safety concerns associated with genetic labels and developing methods to follow cell survival, differentiation and integration with host tissue. Imaging may bridge the gap between cell therapies and health outcomes by elucidating mechanisms of action through longitudinal monitoring.

"Modulation of transcallosal inhibition by bilateral activation of agonist and antagonist proximal arm muscles"
The Journal of Neurophysiology, 111(2):405-14

Mouse over here for a brief summary or click to open article in a new tab.Transcallosal inhibitory interactions between proximal representations in the primary motor cortex remain poorly understood. In this study, we used transcranial magnetic stimulation to examine the ipsilateral silent period (iSP; a measure of transcallosal inhibition) in the biceps and triceps brachii during unilateral and bilateral isometric voluntary contractions.

"Holistic processing for left-right composite faces in Chinese and Caucasian observers"
Visual Cognition, in press:TBD

Mouse over here for a brief summary or click to open article in a new tab.This paper compares the lateralization of face processing amongst Caucasian and Chinese observers given the claims that their hemispheric asymmetries may differ. In fact, using a composite face paradigm, we are unable to observe any differences between the two groups and both process faces configurally to an equivalent extent.

"The nature of face representations in subcortical regions"

Mouse over here for a brief summary or click to open article in a new tab.Given the ontogenetic and phylogenetic findings that indicate that infants and other species are able to perceive faces, we examined the contribution of lower-order (subcortical) regions to face perception. We show a monocular advantage for faces (but not other stimulus types) across a wide range of tasks. These finding are consistent with the claim that pre-striate regions (where monocular segregation is in place) contributes to face perception.

"Balanced neural architecture and the idling brain"
Frontiers in Computational Neuroscience, doi: 10.3389/fncom.2014.00056:

Mouse over here for a brief summary or click to open article in a new tab.Discuss how cortical architectures with a balance between excitation and inhibition shape the spontaneous dynamics in cortical circuits. There is an emphasis on the mechanisms underlying cortical variability.

"Kv7 Channels Regulate Pairwise Spiking Covariability in Health and Disease"
Journal of Neurophysiology, 112:340-352

Mouse over here for a brief summary or click to open article in a new tab.Theoretical investigations on how Kv7 potassium channels control correlation transfer by pairs of spiking neurons.

"Balanced Networks of Spiking Neurons with Spatially Dependent Recurrent Connections"
Physical Review X, 4:021039

Mouse over here for a brief summary or click to open article in a new tab.Incorporates spatial dimensions into the theory of cortical networks with a balance between excitation and inhibition. New conditions on the spread of feedforward and recurrent architectures are derived in the balanced state.

"Successful tactile based visual sensory substitution use functions independently of visual pathway integrity."
Frontiers in Human Neuroscience, 8:291

Mouse over here for a brief summary or click to open article in a new tab.All subjects showed performance improvements using the BrainPort irrespective of nature and duration of blindness. Definite brain areas with significant microstructural integrity changes exist among perinatal blind, acquired blind and normal control subjects, and these variations are most pronounced in the visual pathways. However, the use of sensory substitution devices is feasible irrespective of microstructural integrity of the primary visual pathways between the eye and the brain. Therefore, tongue based devices devices may be usable for a broad array of non-sighted patients.

"Shedding light on learning"
Nature Neuroscience, 17:746-747

Mouse over here for a brief summary or click to open article in a new tab.Brain-computer interfaces (BCIs) and optical imaging have both undergone impressive technological growth in recent years. A study in which mice learn to modulate neural activity merges these technologies to investigate the neural basis of BCI learning with unprecedented spatial detail.

"How may the basal ganglia contribute to auditory categorization and speech perception?"
Frontiers in Neuroscience, 8:230

Mouse over here for a brief summary or click to open article in a new tab.We highlight new research questions that arise in incorporating the broader neuroscience research literature in modeling speech perception, and suggest how understanding contributions of the basal ganglia can inform attempts to optimize training protocols for learning non-native speech categories in adulthood.

"Cortical neurodynamics of inhibitory control."
The Journal of Neuroscience, 34:9551-61

Mouse over here for a brief summary or click to open article in a new tab.The ability to inhibit prepotent responses is critical for successful goal-directed behaviors. To investigate the neural basis of inhibitory control, we conducted a magnetoencephalography study where human participants performed the antisaccade task. Results indicated that neural oscillations in the prefrontal cortex (PFC) showed significant task modulations in preparation to suppress saccades. Before successfully inhibiting a saccade, beta-band power (18-38 Hz) in the lateral PFC and alpha-band power (10-18 Hz) in the frontal eye field (FEF) increased. Trial-by-trial prestimulus FEF alpha-band power predicted successful saccadic inhibition. Further, inhibitory control enhanced cross-frequency amplitude coupling between PFC beta-band (18-38 Hz) activity and FEF alpha-band activity, and the coupling appeared to be initiated by the PFC. Our results suggest a generalized mechanism for top-down inhibitory control: prefrontal beta-band activity initiates alpha-band activity for functional inhibition of the effector and/or sensory system.

"In Defense of Reverse Inference"
British Journal for the Philosophy of Science, 65:251-267

Mouse over here for a brief summary or click to open article in a new tab.Reverse inference is the most commonly used inferential strategy for bringing images of brain activation to bear on psychological hypotheses, but its inductive validity has recently been questioned. In this article, I show that, when it is analyzed in likelihoodist terms, reverse inference does not suffer from the problems highlighted in the recent literature, and I defend the appropriateness of treating reverse inference in these terms.

"Reduced cortical volume and elevated astrocyte density in rats chronically treated with antipsychotic drugs-linking magnetic resonance imaging findings to cellular pathology."
Biological Psychiatry, 75:982-990

Mouse over here for a brief summary or click to open article in a new tab.ncreasing evidence suggests that antipsychotic drugs (APD) might affect brain structure directly, particularly the cerebral cortex. However, the precise anatomical loci of these effects and their underlying cellular basis remain unclear.This study demonstrates region-specific structural effects of chronic APD treatment on the rat cortex, primarily but not exclusively localized to the ACC. At least in the rat, these changes are not due to a loss of either neurons or astrocytes and are likely to reflect a loss of neuropil. Although caution needs to be exerted when extrapolating results from animals to patients, this study highlights the power of this approach to link magnetic resonance imaging findings to their histopathological origins.

"Statistical learning of serial visual transitions by neurons in monkey inferotemporal cortex"
The Journal of Neuroscience, 34:9332

Mouse over here for a brief summary or click to open article in a new tab.If monkeys repeatedly, over the course of weeks, view displays in which two images appear in fixed sequence, then neurons of inferotemporal cortex (ITC) come to exhibit prediction suppression: the response to the trailing image is weaker if it follows the leading image with which it was paired during training than if it follows some other leading image. We demonstrate here that prediction suppression also occurs as a result of exposure to long sequences in which the same image can be both predicted and predicting.

"Subcortical Control of Precision Grip after Human Spinal Cord Injury"
The Journal of Neuroscience, 34(21):7341-7350

Mouse over here for a brief summary or click to open article in a new tab.The motor cortex and the corticospinal system contribute to the control of a precision grip between the thumb and index finger. The involvement of subcortical pathways during human precision grip remains unclear. Using noninvasive cortical and cervicomedullary stimulation, we examined motor evoked potentials (MEPs) and the activity in intracortical and subcortical pathways targeting an intrinsic hand muscle when grasping a small (6 mm) cylinder between the thumb and index finger and during index finger abduction in uninjured humans and in patients with subcortical damage due to incomplete cervical spinal cord injury (SCI). Our results demonstrate that the control of precision grip in humans involves premotoneuronal subcortical mechanisms, likely disynaptic or polysynaptic spinal pathways that are lacking after SCI and restored by long-term use of baclofen. We propose that spinal GABAb-ergic interneuronal circuits, which are sensitive to baclofen, are part of the subcortical premotoneuronal network shaping corticospinal output during human precision grip.

"In Vivo Assessment of Aqueous Humor Dynamics upon Chronic Ocular Hypertension and Hypotensive Drug Treatment using Gadolinium-enhanced MRI"
Invest Ophthalmol Vis Sci, 6:3747

Mouse over here for a brief summary or click to open article in a new tab.Although glaucoma treatments alter aqueous humor (AH) dynamics to lower intraocular pressure, the regulatory mechanisms of AH circulation and their contributions to the pathogenesis of ocular hypertension and glaucoma remain unclear. We hypothesized that gadolinium-enhanced magnetic resonance imaging (Gd-MRI) can visualize and assess AH dynamics upon sustained intraocular pressure elevation and pharmacologic interventions.

"Disrupting Information Coding via Block of 4-AP Sensitive Potassium Channels"
Journal of Neurophysiology, in press:in press

Mouse over here for a brief summary or click to open article in a new tab.ABSTRACT Recent interest has emerged on the role of intrinsic biophysical diversity in neuronal coding. An important question in neurophysiology is understanding which voltage-gated ion channels are responsible for this diversity and how variable expression or activity of one class of ion channels across neurons of a single type affects they way populations carry information. In mitral cells in the olfactory bulb of mice, we found that biophysical diversity was conferred in part by 4-AP (4-aminopyridine) sensitive potassium channels and reduced following block of those channels. When populations of mitral cells were stimulated with identical inputs, the diversity exhibited in their output spike patterns reduced with the addition of 4-AP, decreasing the stimulus information carried by ensembles of 15 neurons from 437±15 bits/sec in to 397±19 bits/sec. Decreases in information were due to reduction in the diversity of population spike patterns generated in response to different features of the stimulus, suggesting that the coding capacity of a population can be altered by changes in function of single ion channel types.

"Greater Excitability and Firing Irregularity of Tufted Cells Underlies Distinct Afferent-Evoked Activity of Olfactory Bulb Mitral and Tufted Cells"
Journal of Physiology, 592:2097-2118

Mouse over here for a brief summary or click to open article in a new tab.Mitral and tufted cells, the two classes of principal neurons in the mammalian main olfactory bulb, exhibit morphological differences but remain widely viewed as functionally equivalent. Results from several recent studies, however, suggest that these two cell classes may encode complementary olfactory information in their distinct patterns of afferent‐evoked activity. To understand how these differences in activity arise, we have performed the first systematic comparison of synaptic and intrinsic properties between mitral and tufted cells. Consistent with previous studies, we found that tufted cells fire with higher probability and rates and shorter latencies than mitral cells in response to physiological afferent stimulation. This stronger response of tufted cells could be partially attributed to synaptic differences, as tufted cells received stronger afferent‐evoked excitation than mitral cells. However, differences in intrinsic excitability also contributed to the differences between mitral and tufted cell activity. Compared to mitral cells, tufted cells exhibited twofold greater excitability and peak instantaneous firing rates. These differences in excitability probably arise from differential expression of voltage‐gated potassium currents, as tufted cells exhibited faster action potential repolarization and afterhyperpolarizations than mitral cells. Surprisingly, mitral and tufted cells also showed firing mode differences. While both cell classes exhibited regular firing and irregular stuttering of action potential clusters, tufted cells demonstrated a greater propensity to stutter than mitral cells. Collectively, stronger afferent‐evoked excitation, greater intrinsic excitability and more irregular firing in tufted cells can combine to drive distinct responses of mitral and tufted cells to afferent‐evoked input.

"Is inner speech the basis of auditory verbal hallucination in schizophrenia?"
Frontiers: Psychiatry, 5:75

Mouse over here for a brief summary or click to open article in a new tab.We discuss what might be meant by "inner speech" and argue that one form of inner speech, inner articulation, is not likely the substrate of typical auditory verbal hallucination in schizophrenia.