Stiffness map of the grasping contact areas of the human hand

The elasticity and damping of the soft tissues of the hand contribute to dexterity while grasping and also help to stabilise the objects in manipulation tasks. Although some previous works have studied the force-displacement response of the fingertips, the responses in all other regions of the hand that usually participate in grasping have not been analysed to date. In this work we performed experimental measurements in 20 subjects to obtain a stiffness map of the different grasping contact areas of the human hand. A force-displacement apparatus was used to simultaneously measure force and displacement at 39 different points on the hand at six levels of force ranging from 1 N to 6 N. A non-linear force-displacement response was found for all points, with stiffness increasing with the amount of force applied. Mean stiffness for the different points and force levels was within the range from 0.2 N/mm to 7.7 N/mm. However, the stiffness range and variation with level of force were found to be different from point to point. A total of 13 regions with similar stiffness behaviours were identified. The stiffness in the fingertips increased linearly with the amount of force applied, while in the palm it remained more constant for the range of forces considered. It is hypothesised that the differences in the stiffness behaviour from one region to another allow these regions to play different roles during grasping.     

Convergence and divergence are mostly reciprocated properties of the connections in the network of cortical areas

Cognition is based on the integrated functioning of hierarchically organized cortical processing streams in a manner yet to be clarified. Because integration fundamentally depends on convergence and the complementary notion of divergence of the neuronal connections, we analysed integration by measuring the degree of convergence/divergence through the connections in the network of cortical areas. By introducing a new index, we explored the complementary convergent and divergent nature of connectional reciprocity and delineated the backward and forward cortical sub-networks for the first time. Integrative properties of the areas defined by the degree of convergence/divergence through their afferents and efferents exhibited distinctive characteristics at different levels of the cortical hierarchy. Areas previously identified as hubs exhibit information bottleneck properties. Cortical networks largely deviate from random graphs where convergence and divergence are balanced at low reciprocity level. In the cortex, which is dominated by reciprocal connections, balance appears only by further increasing the number of reciprocal connections. The results point to the decisive role of the optimal number and placement of reciprocal connections in large-scale cortical integration. Our findings also facilitate understanding of the functional interactions between the cortical areas and the information flow or its equivalents in highly recurrent natural and artificial networks.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE₂, PGE₁, PGI₂). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE₁, PGE₂, PGI₂) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maximas. The results suggest that renal PGs (PGE₂ and PGI₂) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.     

Interactions between janus and bcd cortical pattern mutants in Tetrahymena thermophila

Summary An analysis of bcd, janA; bcd, janB; and bcd, janC double-mutant phenotypes in Tetrahymena thermophila has allowed us to examine patterning processes affected by two different classes of mutations. bcd brings about a broadening of the oral and contractile vacuole pore domains in the ciliate cortex, while the janus mutations generate a mirror-image duplication of the ventral cortical pattern. We observed both bcd and janus characteristics expressed in the double mutants, as well as features unique to the double-mutant. Temperature-shift experiments employing the temperature-sensitive janB mutation in a double-mutant (bcd, janB) combination allowed us to observe the changes in pattern as a mirror-image geometry was brought into expression and subsequently removed within the bcd, janB double homozygote. These experiments suggest that there are multiple pattern-mechanisms at work with differing kinetics of expression in the ciliate cortex. We discuss how the bcd mutation could influance expression of the janus mutations in light of a model previously proposed to account for the janus phenotype.     

Interaction between influences of functionally different cortical areas on caudate neurons in cats

Unit activity in the caudate nucleus evoked by paired stimulation of the anterior sigmoid and middle suprasylvian gyri was studied in acute experiments on cats. Responses in most neurons to testing stimulation of the anterior sigmoid gyrus during the period of inhibition of spontaneous activity evoked by conditioning stimulation of the suprasylvian gyrus were preserved, but in isolated cases they were actually facilitated. Meanwhile conditioning stimulation of the anterior sigmoid gyrus in the period of inhibition depressed responses to testing stimulation of the suprasylvian gyrus. Similar results were obtained in experiments on animals with deep transcortical sections between the sensomotor and parietal regions, ruling out the possibility of interaction between the stimulated zones at the cortical level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 142–148, March–April, 1981.     

Neural network analysis of the pattern of functional connectivity between cerebral areas in schizophrenia

 Recent evidence suggests that the core abnormality of cerebral function in schizophrenia is a disruption of functional connectivity between diverse cerebral sites. Functional connectivity is defined as the correlation between neuronal activity at remote sites. It can be measured using functional imaging techniques such as positron emission tomography (PET). This paper reports an analysis using a neural network to discriminate between the patterns of functional connectivity in schizophrenic patients and healthy subjects. The data was derived from a PET study of regional cerebral blood flow during word generation in 6 healthy subjects and 16 schizophrenic patients with established illness, in whom the clinical diagnosis could be made with confidence. After training on data from two healthy subjects and seven schizophrenic patients, the neural network successfully assigned all members of a test set of four healthy subjects and nine schizophrenic patients to the correct diagnostic category. While this result should be interpreted with caution on account of the small sample size, it indicates that neural network analysis is potentially of value in the diagnosis of schizophrenia. Received: 2 August 1999 / Accepted in revised form: 30 June 2000     

Fast,cell-resolution,contiguous-wide two-photon imaging to reveal functional network architectures across multi-modal cortical areas

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Interactions involved in grasping and locking of the inhibitory peptide IF1 by mitochondrial ATP synthase

When mitochondria become deenergized, futile ATP hydrolysis is prevented by reversible binding of an endogenous inhibitory peptide called IF1 to ATP synthase. Between initial IF1 binding and IF1 locking the enzyme experiences large conformational changes. While structural studies give access to analysis of the dead-end inhibited state, transient states have thus far not been described. Here, we studied both initial and final states by reporting, for the first time, the consequences of mutations of Saccharomyces cerevisiae ATP synthase on its inhibition by IF1. Kinetic studies allowed the identification of amino acids or motifs of the enzyme that are involved in recognition and/or locking of IF1 α-helical midpart. This led to an outline of IF1 binding process. In the recognition step, protruding parts of α and especially β subunits grasp IF1, most likely by a few residues of its α-helical midpart. Locking IF1 within the αβ interface involves additional residues of both subunits. Interactions of the α and β subunits with the foot of the γ subunit might contribute to locking and stabilizing of the dead-end state.     

Cross-modal interactions between olfaction and vision when grasping

This study used kinematics to investigate the integration between vision and olfaction during grasping movements. Participants were requested to smell an odorant and then grasp an object presented in central vision. The results indicate that if the target was small (e.g., a strawberry), the time and amplitude of maximum hand aperture were later and greater, respectively, when the odor evoked a larger object (e.g., an orange) than when the odor evoked an object of a similar size as the target or no odor was presented. Conversely, the time and amplitude of maximum hand aperture were earlier and reduced, respectively, when the target was large (e.g., a peach) and the odor evoked a smaller sized object (e.g., an almond) than when the odor evoked an object of a similar size as the target or no odor was presented. Taken together, these results support the evidence of cross-modal links between olfaction and vision and extend this notion to goal-directed actions.     

Recovery after damage to motor cortical areas

Until recently, the neural bases underlying recovery of function after damage to the cerebral cortex were largely unknown. Recent results from neuroanatomical and neurophysiological studies in animal models have demonstrated that after cortical damage, long-term and widespread structural and functional alterations take place in the spared cortical tissue. These presumably adaptive changes may play an important role in functional recovery.     

Dispersion along fiber tracts and in the coupling between tracts and a cortical network.

Dispersion in a neuronal coritcal network was modeled using CSMP, a Continuous Systems Modeling Program. The signal dispersion over pathways was simulated by use of a serial product approximating the convolution integral. The program was written in a sufficiently general format to be applied to a variety of biological signals. Calculated signals from a fiber tract and activation of a cortical network were compared with experimental data from cats. The network consists of excitatory cells in a forward limb which send collaterals to interneurons that, once excited, feed back to inhibit the excitatory cells. The model was consistent with data from neuronal assemblies in the prepyriform cortex and fibers in the lateral olfactory tract.     

Development and plasticity of cortical areas and networks

The development of cortical layers, areas and networks is mediated by a combination of factors that are present in the cortex and are influenced by thalamic input. Electrical activity of thalamocortical afferents has a progressive role in shaping cortex. For early thalamic innervation and patterning, the presence of activity might be sufficient; for features that develop later, such as intracortical networks that mediate emergent responses of cortex, the spatiotemporal pattern of activity often has an instructive role. Experiments that route projections from the retina to the auditory pathway alter the pattern of activity in auditory thalamocortical afferents at a very early stage and reveal the progressive influence of activity on cortical development. Thus, cortical features such as layers and thalamocortical innervation are unaffected, whereas features that develop later, such as intracortical connections, are affected significantly. Surprisingly, the behavioural role of 'rewired' cortex is also influenced profoundly, indicating the importance of patterned activity for this key aspect of cortical function.     

Functional specialization of seven mouse visual cortical areas

To establish the mouse as a genetically tractable model for high-order visual processing, we characterized fine-scale retinotopic organization of visual cortex and determined functional specialization of layer 2/3 neuronal populations in seven retinotopically identified areas. Each area contains a distinct visuotopic representation and encodes a unique combination of spatiotemporal features. Areas LM, AL, RL, and AM prefer up to three times faster temporal frequencies and significantly lower spatial frequencies than V1, while V1 and PM prefer high spatial and low temporal frequencies. LI prefers both high spatial and temporal frequencies. All extrastriate areas except LI increase orientation selectivity compared to V1, and three areas are significantly more direction selective (AL, RL, and AM). Specific combinations of spatiotemporal representations further distinguish areas. These results reveal that mouse higher visual areas are functionally distinct, and separate groups of areas may be specialized for motion-related versus pattern-related computations, perhaps forming pathways analogous to dorsal and ventral streams in other species.     

Functional specialization of mouse higher visual cortical areas

The mouse is emerging as an important model for understanding how sensory neocortex extracts cues to guide behavior, yet little is known about how these cues are processed beyond primary cortical areas. Here, we used two-photon calcium imaging in awake mice to compare visual responses in primary visual cortex (V1) and in two downstream target areas, AL and PM. Neighboring V1 neurons had diverse stimulus preferences spanning five octaves in spatial and temporal frequency. By contrast, AL and PM neurons responded best to distinct ranges of stimulus parameters. Most strikingly, AL neurons preferred fast-moving stimuli while PM neurons preferred slow-moving stimuli. By contrast, neurons in V1, AL, and PM demonstrated similar selectivity for stimulus orientation but not for stimulus direction. Based on these findings, we predict that area AL helps guide behaviors involving fast-moving stimuli (e.g., optic flow), while area PM?helps guide behaviors involving slow-moving objects.     

Revealing instances of coordination among multiple cortical areas

Cognitive functions must involve interactions between several (perhaps many) cortical regions. The instances of such interactions may not be tightly time locked to any external cue. Thus averaging over repeated trials of brain activity or its spectrograms may miss these instances. Here, coordinated activity among multiple cortical locations is revealed in ongoing activity with millisecond accuracy without the need for averaging over time or frequencies. This is based on reconstructions of the cortical current dipole amplitudes at multiple points from MEG recordings. In these current dipole traces, instances of brief activity undulations (BAUs) are automatically detected and used to reveal where and when cortical points interact. The article shows that these BAUs truly represent the reorganization of activity at the cortex and are strongly connected to behavior.     

A computational framework for topographies of cortical areas

Self-organizing feature maps (SOFMs) represent a dimensionality-reduction algorithm that has been used to replicate feature topographies observed experimentally in primary visual cortex (V1). We used the SOFM algorithm to model possible topographies of generic sensory cortical areas containing up to five arbitrary physiological features. This study explored the conditions under which these multi-feature SOFMs contained two features that were mapped monotonically and aligned orthogonally with one another (i.e., “globally orthogonal”), as well as the conditions under which the map of one feature aligned with the longest anatomical dimension of the modeled cortical area (i.e., “dominant”). In a single SOFM with more than two features, we never observed more than one dominant feature, nor did we observe two globally orthogonal features in the same map in which a dominant feature occurred. Whether dominance or global orthogonality occurred depended upon how heavily weighted the features were relative to one another. The most heavily weighted features are likely to correspond to those physical stimulus properties transduced directly by the sensory epithelium of a particular sensory modality. Our results imply, therefore, that in the primary cortical area of sensory modalities with a two-dimensional sensory epithelium, these two features are likely to be organized globally orthogonally to one another, and neither feature is likely to be dominant. In the primary cortical area of sensory modalities with a one-dimensional sensory epithelium, however, this feature is likely to be dominant, and no two features are likely to be organized globally orthogonally to one another. Because the auditory system transduces a single stimulus feature (i.e., frequency) along the entire length of the cochlea, these findings may have particular relevance for topographic maps of primary auditory cortex. This research was supported by The McDonnell Center for Higher Brain Function, The Wallace H. Coulter Foundation and NIH grant DC008880.