Coding of cognitive magnitude: compressed scaling of numerical information in the primate prefrontal cortex

Whether cognitive representations are better conceived as language-based, symbolic representations or perceptually related, analog representations is a subject of debate. If cognitive processes parallel perceptual processes, then fundamental psychophysical laws should hold for each. To test this, we analyzed both behavioral and neuronal representations of numerosity in the prefrontal cortex of rhesus monkeys. The data were best described by a nonlinearly compressed scaling of numerical information, as postulated by the Weber-Fechner law or Stevens' law for psychophysical/sensory magnitudes. This nonlinear compression was observed on the neural level during the acquisition phase of the task and maintained through the memory phase with no further compression. These results suggest that certain cognitive and perceptual/sensory representations share the same fundamental mechanisms and neural coding schemes.     

A variational approach to behavioral and neuroelectrical laws

Variational methods play a fundamental and unifying role in several fields of physics, chemistry, engineering, economics, and biology, as they allow one to derive the behavior of a system as a consequence of an optimality principle. A possible application of these methods to a model of perception is given by considering a psychophysical law as the solution of an Euler-Lagrange equation. A general class of Lagrangians is identified by requiring the measurability of prothetic continua on interval scales. The associated Hamiltonian (the energy of the process) is tentatively connected with neurophysiological aspects. As an example of the suggested approach a particular choice of the Lagrangian, that is a sufficient condition to obtain classical psychophysical laws, while accounting for psychophysical adaptation and the stationarity of neuronal activity, is used to explore a possible relation between a behavioral law and a neuroelectrical ,response based on the Naka-Rushton model.     

Positive Effect of Noises on Sensory Systems

1　IntroductionStochasticresonanceisthe phenomenonthatanonzeronoiseleveloptimizesthesystemperformanceinnon linearfield .Especially ,ithelpstodetectandtransferthesmallsignalinalargenoisybackground .Inthenondynamicalsystemorthethresholddetectionsys tem ,thethresholdcrossingisatypicalnon linearphe nomenonandcanresultinastochasticresonance[1] .Asingleneuronwiththresholdbehaviorcanberegardedasasimplethresholddetector ;hencethestochasticres onancephenomenaofneuronhavenaturallybeenstud ied[2 ,3] .Re…     

Timing in the absence of clocks: encoding time in neural network states

Decisions based on the timing of sensory events are fundamental to sensory processing. However, the mechanisms by which the brain measures time over ranges of milliseconds to seconds remain unclear. The dominant model of temporal processing proposes that an oscillator emits events that are integrated to provide a linear metric of time. We examine an alternate model in which cortical networks are inherently able to tell time as a result of time-dependent changes in network state. Using computer simulations we show that within this framework, there is no linear metric of time, and that a given interval is encoded in the context of preceding events. Human psychophysical studies were used to examine the predictions of the model. Our results provide theoretical and experimental evidence that, for short intervals, there is no linear metric of time, and that time may be encoded in the high-dimensional state of local neural networks.     

A model of olfactory adaptation and sensitivity enhancement in the olfactory bulb

It has been suggested that the olfactory bulb, the first processing center after the sensory cells in the olfactory pathway, plays a role in olfactory adaptation, odor sensitivity enhancement by motivation and other olfactory psychophysical phenomena. In a mathematical model based on the bulbar anatomy and physiology, the inputs from the higher olfactory centers to the inhibitory cells in the bulb are shown to be able to modulate the response, and thus the sensitivity of the bulb to specific odor inputs. It follows that the bulb can decrease its sensitivity to a pre-existing and detected odor (adaptation) while remaining sensitive to new odors, or increase its sensitivity to interested searching odors. Other olfactory psychophysical phenomena such as cross-adaptation etc. are discussed as well.     

On the laws of psychophysics

Experiments by S. S. Stevens (Stevens, 1957, and Stevens and Galanter, 1957) and his collaborators indicate that the so-called logarithmic Weber-Fechner Law is not realized in most human perceptions. Instead, a power law seems to emerge over a large number of sensory continua. This is important because for a long time the logarithmic law was looked upon as almost the only possible psychophysical law. The logarithmic law appeared desirable intuitively because it made the sensation depend on the relative values of the stimuli and not on their absolute values. This is, of course, useful for evolutionary reasons. Some other reasons are also discussed by Stevens (1961).     

An initial ‘snapshot’ of sensory information biases the likelihood and speed of subsequent changes of mind

We often need to rapidly change our mind about perceptual decisions in order to account for new information and correct mistakes. One fundamental, unresolved question is whether information processed prior to a decision being made (‘pre-decisional information’) has any influence on the likelihood and speed with which that decision is reversed. We investigated this using a luminance discrimination task in which participants indicated which of two flickering greyscale squares was brightest. Following an initial decision, the stimuli briefly remained on screen, and participants could change their response. Using psychophysical reverse correlation, we examined how moment-to-moment fluctuations in stimulus luminance affected participants’ decisions. This revealed that the strength of even the very earliest (pre-decisional) evidence was associated with the likelihood and speed of later changes of mind. To account for this effect, we propose an extended diffusion model in which an initial ‘snapshot’ of sensory information biases ongoing evidence accumulation.     

A-type GABA receptor as a central target of TRPM8 agonist menthol

Menthol is a widely-used cooling and flavoring agent derived from mint leaves. In the peripheral nervous system, menthol regulates sensory transduction by activating TRPM8 channels residing specifically in primary sensory neurons. Although behavioral studies have implicated menthol actions in the brain, no direct central target of menthol has been identified. Here we show that menthol reduces the excitation of rat hippocampal neurons in culture and suppresses the epileptic activity induced by pentylenetetrazole injection and electrical kindling in vivo. We found menthol not only enhanced the currents induced by low concentrations of GABA but also directly activated GABA(A) receptor (GABA(A)R) in hippocampal neurons in culture. Furthermore, in the CA1 region of rat hippocampal slices, menthol enhanced tonic GABAergic inhibition although phasic GABAergic inhibition was unaffected. Finally, the structure-effect relationship of menthol indicated that hydroxyl plays a critical role in menthol enhancement of tonic GABA(A)R. Our results thus reveal a novel cellular mechanism that may underlie the ambivalent perception and psychophysical effects of menthol and underscore the importance of tonic inhibition by GABA(A)Rs in regulating neuronal activity.     

Fingerprint lines may not directly affect SA-I mechanoreceptor response

Understanding how skin microstructure affects slowly adapting type I (SA-I) mechanoreceptors in encoding edge discontinuities is fundamental to understanding our sense of touch. Skin microstructure, in particular papillary ridges, has been thought to contribute to edge and gap sensation. Cauna's 1954 model of touch sensibility describes a functional relationship between papillary ridges and edge sensation. His lever arm model proposes that the papillary ridge (exterior fingerprint line) and underlying intermediate ridge operate as a single unit, with the intermediate ridge acting as a lever which magnifies indentation imposed at the papillary ridge. This paper contests the validity of the lever arm model. While correctly representing the anatomy, this mechanism inaccurately characterizes the function of the papillary ridges. Finite element analysis and assessment of the critical anatomy indicate that papillary ridges have little direct effect on how SA-I receptors respond to the indentation of static edges. Our analysis supports a revised (stiff shell-elastic bending support) interpretation where the epidermis is split into two major layers with a stiff, deformable shell over an elastic bending support. Recent physiological, electrophysiological, and psychophysical findings support our conclusion that the function of the intermediate ridge is distinct from the function of the papillary ridge.     

Sensing and deciding in the somatosensory system.

Combined psychophysical and neurophysiological experiments have revealed some of the neural codes associated with perception and processing of tactile information. Recently, intracortical microstimulation was used to demonstrate a causal link between primary cortical activity and perception. Evidence for a subsequent link, between a sensory decision process and its expression as a movement, has been found in motor areas.     

An Equiratio Mixture Model for Non-additive Components: A Case Study for Aspartame/Acesulfame-K Mixtures

The Equiratio Mixture Model predicts the psychophysical functionfor an equiratio mixture type on the basis of the psychophysicalfunctions for the unmixed components. The model reliably estimatesthe sweetness of mixtures of sugars and sugar-alchohols, butis unable to predict intensity for aspartame/sucrose mixtures.In this paper, the sweetness of aspartame/acesulfame-K mixturesin aqueous and acidic solutions is investigated. These two intensivesweeteners probably do not comply with the model's originalassumption of sensory dependency among components. However,they reveal how the Equiratio Mixture Model could be modifiedto describe and predict mixture functions for non-additive substances. To predict equiratio functions for all similar tasting substances,a new Equiratio Mixture Model should yield accurate predictionsfor components eliciting similar intensities at widely differingconcentration levels, and for substances exhibiting hypo- orhyperadditivity. In addition, it should be able to correct violationsof Stevens's power law. These three problems are resolved ina model that uses equi-intense units as the measure of physicalconcentration. An interaction index in the formula for the constantaccounts for the degree of interaction between mixture components.Deviations from the power law are corrected by a nonlinear responseoutput transformation, assuming a two-stage model of psychophysicaljudgment. Chem. Senses 21: 1–11, 1996.     

Electromuscular incapacitation results from stimulation of spinal reflexes

Electronic stun devices (ESD) often used in law enforcement, military action or self defense can induce total body uncoordinated muscular activity, also known as electromuscular incapacitation (EMI). During EMI the subject is unable to perform purposeful or coordinated movements. The mechanism of EMI induction has not been reported, but has been generally thought to be direct muscle and nerve excitation from the fields generated by ESDs. To determine the neuromuscular mechanisms linking ESD to induction of EMI, we investigated EMI responses using an anesthetized pig model. We found that EMI responses to ESD application can best be simulated by simultaneous stimulation of motor and sensory peripheral nerves. We also found that application of local anesthetics limited the response of ESD to local muscle stimulation and abolished the total body EMI response. Stimulation of the pure sensory peripheral nerves or nerves that are primarily motor nerves induced muscle responses that are consistent with well defined spinal reflexes. These findings suggest that the mechanism of ESD‐induced EMI is mediated by excitation of multiple simultaneous spinal reflexes. Although direct motor‐neuron stimulation in the region of ESD contact may significantly add to motor reactions from ESD stimulation, multiple spinal reflexes appear to be a major, and probably the dominant mechanism in observed motor response. Bioelectromagnetics 30:411–421, 2009. © 2009 Wiley‐Liss, Inc.     

Paradoxical evidence integration in rapid decision processes

Decisions about noisy stimuli require evidence integration over time. Traditionally, evidence integration and decision making are described as a one-stage process: a decision is made when evidence for the presence of a stimulus crosses a threshold. Here, we show that one-stage models cannot explain psychophysical experiments on feature fusion, where two visual stimuli are presented in rapid succession. Paradoxically, the second stimulus biases decisions more strongly than the first one, contrary to predictions of one-stage models and intuition. We present a two-stage model where sensory information is integrated and buffered before it is fed into a drift diffusion process. The model is tested in a series of psychophysical experiments and explains both accuracy and reaction time distributions.     

Flutter discrimination: neural codes,perception, memory and decision making

Recent studies combining psychophysical and neurophysiological experiments in behaving monkeys have provided new insights into how several cortical areas integrate efforts to solve a vibrotactile discrimination task. In particular, these studies have addressed how neural codes are related to perception, working memory and decision making in this model. The primary somatosensory cortex drives higher cortical areas where past and current sensory information are combined, such that a comparison of the two evolves into a behavioural decision. These and other observations in visual tasks indicate that decisions emerge from highly-distributed processes in which the details of a scheduled motor plan are gradually specified by sensory information.     

Statistical criteria for the cytology of gastric cancer a proposal of distance index.

The concept and term of Distance Index, a complex ratio of cell, nucleus and nucleolus has been previously reported by the author. Twenty were sampled from thirty-four advanced cancers, twenty-one early cancers and six benign atypical lesions for this stochastical diagnostics. Distance Index was proved to have better diagnostic value in separatings the gastric cancer and the benign epithelium than the nuclear cell ratio and the nucleolar cell ratio. It has been found that the value of the constant K is most suitable at 130.     

The dynamics of velocity adaptation in human vision

Since Barlow and Hill's classic study of the adaptation of the rabbit ganglion cell to movement [1], there have been several reports that motion adaptation is accompanied by an exponential reduction in spike rate, and similar estimates of the time course of velocity adaptation have been found across species [2-4]. Psychophysical studies in humans have shown that perceived velocity may reduce exponentially with adaptation [5,6]. It has been suggested that the reduction in firing of single cells may constitute the neural substrate of the reduction in perceived speed in humans [1,5-7]. Although a model of velocity coding in which the firing rate directly encodes speed may have the advantage of simplicity, it is not supported by psychophysical research. Furthermore, psychophysical estimates of the time course of perceived speed adaptation are not entirely consistent with physiological estimates. This discrepancy between psychophysical and physiological estimates may be due to the unrealistic assumption that speed is coded in the gross spike rate of neurons in the primary visual cortex. The psychophysical data on motion processing are, however, generally consistent with a model in which perceived velocity is derived from the ratio of two temporal channels [8-14]. We have examined the time course of speed adaptation and recovery to determine whether the observed rates can be better related to the established physiology if a ratio model of velocity processing is assumed. Our results indicate that such a model describes the data well and can accommodate the observed difference in the time courses of physiological and psychophysical processes.     

Visuovestibular perception of self-motion modeled as a dynamic optimization process

 This article describes a computational model for the sensory perception of self-motion, considered as a compromise between sensory information and physical coherence constraints. This compromise is realized by a dynamic optimization process minimizing a set of cost functions. Measure constraints are expressed as quadratic errors between motion estimates and corresponding sensory signals, using internal models of sensor transfer functions. Coherence constraints are expressed as quadratic errors between motion estimates, and their prediction is based on internal models of the physical laws governing the corresponding physical stimuli. This general scheme leads to a straightforward representation of fundamental sensory interactions (fusion of visual and canal rotational inputs, identification of the gravity component from the otolithic input, otolithic contribution to the perception of rotations, and influence of vection on the subjective vertical). The model is tuned and assessed using a range of well-known psychophysical results, including off-vertical axis rotations and centrifuge experiments. The ability of the model to predict and help analyze new situations is illustrated by a study of the vestibular contributions to self-motion perception during automobile driving and during acceleration cueing in driving simulators. The extendable structure of the model allows for further developments and applications, by using other cost functions representing additional sensory interactions. Received: 10 October 2000 / Accepted in revised form: 12 August 2002 Acknowledgements. This research was performed within the framework of a CIFRE grant (ANRT contract #331/97) for the doctoral work of G. Reymond at RENAULT and LPPA. The authors wish to thank the anonymous reviewers and Prof. H. Mittelstaedt for their valuable suggestions. Correspondence to: G. Reymond (e-mail: gilles.reymond@renault.com, Tel.: +33-1-34952170, Fax: +33-1-34952730)     

Individual factors in nasal chemesthesis

Population variability in nasal irritant (chemesthesic) sensitivity has been postulated by both clinicians and epidemiologists studying indoor and ambient air pollution. Among experimentalists, however, limited attention has been paid to variance in this trait. Candidate susceptibility markers include age, gender, presence or absence of nasal allergies or olfactory dysfunction, cognitive bias and self-reported pollutant reactivity. For most of these markers, conflicting data exist. This review distinguishes between functional subcomponents of nasal irritant sensitivity (sensory acuity versus physiologic reactivity), catalogs psychophysical and physiological methods for their study and examines the current evidence for variation in this trait. In general, interindividual variability has been an under-studied phenomenon.