Electrographical correlates of adequate and erroneous responses caused by conditioned signals of different functional sign during instrumental conditioning in dogs

Power spectral (in the broad frequency band of 1-225 Hz) of short-term (less than 1 s) EEG reactions were studied in dogs in the course of instrumental food conditioning. These reactions appeared in different cortical areas in response to differentiating signals under conditions of both adequate and erroneous responses. The EEG power of such reactions was several times lower as compared to responses to positive signals, mainly, at the expense of the frequencies in the band of 90-225 Hz (the power of which was higher than that of the traditional band of 1-30 Hz and the gamma band of 30-80 Hz). The frequency composition of EEG reactions accompanying adequate responses was defined, mainly, by discrete subgroups of high-frequency components. During erroneous responses, the discrete structure of the corresponding EEG reactions was broken.     

Different origins of gamma rhythm and high-gamma activity in macaque visual cortex

During cognitive tasks electrical activity in the brain shows changes in power in specific frequency ranges, such as the alpha (8-12 Hz) or gamma (30-80 Hz) bands, as well as in a broad range above ～80 Hz, called the high-gamma band. The role or significance of this broadband high-gamma activity is unclear. One hypothesis states that high-gamma oscillations serve just like gamma oscillations, operating at a higher frequency and consequently at a faster timescale. Another hypothesis states that high-gamma power is related to spiking activity. Because gamma power and spiking activity tend to co-vary during most stimulus manipulations (such as contrast modulations) or cognitive tasks (such as attentional modulation), it is difficult to dissociate these two hypotheses. We studied the relationship between high-gamma power, gamma rhythm, and spiking activity in the primary visual cortex (V1) of awake monkeys while varying the stimulus size, which increased the gamma power but decreased the firing rate, permitting a dissociation. We found that gamma power became anti-correlated with the high-gamma power, suggesting that the two phenomena are distinct and have different origins. On the other hand, high-gamma power remained tightly correlated with spiking activity under a wide range of stimulus manipulations. We studied this relationship using a signal processing technique called Matching Pursuit and found that action potentials are associated with sharp transients in the LFP with broadband power, which is visible at frequencies as low as ～50 Hz. These results distinguish broadband high-gamma activity from gamma rhythms as an easily obtained and reliable electrophysiological index of neuronal firing near the microelectrode. Further, they highlight the importance of making a careful dissociation between gamma rhythms and spike-related transients that could be incorrectly decomposed as rhythms using traditional signal processing methods.     

Gamma oscillations in primate primary visual cortex are severely attenuated by small stimulus discontinuities

Gamma oscillations (30 to 80 Hz) have been hypothesized to play an important role in feature binding, based on the observation that continuous long bars induce stronger gamma in the visual cortex than bars with a small gap. Recently, many studies have shown that natural images, which have discontinuities in several low-level features, do not induce strong gamma oscillations, questioning their role in feature binding. However, the effect of different discontinuities on gamma has not been well studied. To address this, we recorded spikes and local field potential from 2 monkeys while they were shown gratings with discontinuities in 4 attributes: space, orientation, phase, or contrast. We found that while these discontinuities only had a modest effect on spiking activity, gamma power drastically reduced in all cases, suggesting that gamma could be a resonant phenomenon. An excitatory–inhibitory population model with stimulus-tuned recurrent inputs showed such resonant properties. Therefore, gamma could be a signature of excitation–inhibition balance, which gets disrupted due to discontinuities.

Gamma oscillations (30-80 Hz) in visual cortex have been hypothesized to play an important role in feature binding, but this role has recently been questioned. This study shows that visual stimulus-induced gamma oscillations are highly attenuated with even small discontinuities in the stimulus. This "resonant" behaviour can be explained by a simple excitatory-inhibitory model in which discontinuities lead to a small reduction in lateral inputs.     

Electrographic correlates of "inner states" caused by positive conditioned stimuli in the course of instrumental conditioning in dogs

Energy characteristics (power spectra) of short-term (less than 1 s) EEG-reactions were studied in dogs in the course of instrumental conditioning. These reactions were observed in different areas of the cortex during selective attention in response to positive conditioned stimuli. They immediately preceded strong blow with a paw on the pedal of feeding cup and taking the reward. The EEG power at these moments was 1.5-3 times higher than the baseline EEG power level in a prestimulus period. The high-frequency structure of corresponding EEG reactions comprised discrete individual spectral peaks both in traditional (1-30 Hz) and gamma (30-80 Hz) ranges and higher-frequency components (80-200 Hz) as well. In some cases, the higher-frequency components (80-200 Hz) were most pronounced.     

Regional features of electrical reactions (in the frequency band of 1-225 Hz) in the cerebral cortex to conditioned stimuli in the course of instrumental conditioning

Power spectra of short-term (less than 1 s) EEG-reactions (in the frequency band of 1-225 Hz) were studied in dogs in the course of instrumental food conditioning. These reactions were observed in different areas of the cortex in response to positive and differentiated conditioned stimuli. Regional features between the spectra were found both in the power level and frequency structure. The power of the reactions in the visual and parietal areas of the left hemisphere was higher than in the motor areas. Power spectra of reactions to differentiated stimuli were significantly lower than the spectra of reactions to positive stimuli mainly owing to the high-frequency components (80-225 Hz). In these both cases, prestimulus power spectra did not differ. The frequency structure of corresponding EEG-reactions consisted of individual spectral peaks, mainly both gamma (30-80 Hz) and higher-frequency (80-225 Hz) bands.     

Synchronization of olfactory bulb mitral cells by precisely timed inhibitory inputs

Synchronized oscillatory activity at the gamma frequency (30-70 Hz) is thought to be important for information processing in many sensory systems. Here, I used patch-clamp recordings in neuron pairs in rat olfactory bulb slices to assess the mechanisms underlying such "gamma" activity in the olfactory system. Patterned electrical stimulation of afferents that mimicked a natural odor stimulus elicited rapidly synchronized spikes (lag < or = 5 ms) in mitral cells, along with oscillatory activity at the gamma (approximately 50 Hz) frequency. Analysis of coupling potentials, combined with dendritic sectioning, indicated that mitral cell synchrony was mainly driven by inhibitory postsynaptic potentials (IPSPs) imposed by GABAergic granule cells. Recordings in granule cell pairs indicated that granule cells were themselves synchronized by their excitatory inputs from mitral cells, providing a means to coordinate GABA release. These results demonstrate that rapid synchrony can emerge in a network through the precise back-and-forth interplay between neuronal populations.     

Spatially localized distortions of event time

A fundamental question about the perception of time is whether the neural mechanisms underlying temporal judgements are universal and centralized in the brain or modality specific and distributed. Time perception has traditionally been thought to be entirely dissociated from spatial vision. Here we show that the apparent duration of a dynamic stimulus can be manipulated in a local region of visual space by adapting to oscillatory motion or flicker. This implicates spatially localized temporal mechanisms in duration perception. We do not see concomitant changes in the time of onset or offset of the test patterns, demonstrating a direct local effect on duration perception rather than an indirect effect on the time course of neural processing. The effects of adaptation on duration perception can also be dissociated from motion or flicker perception per se. Although 20 Hz adaptation reduces both the apparent temporal frequency and duration of a 10 Hz test stimulus, 5 Hz adaptation increases apparent temporal frequency but has little effect on duration perception. We conclude that there is a peripheral, spatially localized, essentially visual component involved in sensing the duration of visual events.     

A behavioral study of vibrational sensitivity in the pigeon (Columba livia)

Summary The pigeon (Columba livia) has a well-developed ability to detect weak vibrations. Using the method of heart-rate conditioning the vibrational sensitivity was determined for four pigeons at an error probability of P<0.025. The threshold-frequency relationships indicate that the greatest sensitivity to vibrational stimuli is found in the frequency range from 300 to 1,000 Hz with thresholds of about 0.1 m; lowest threshold is 0.04 m at 500 Hz (Fig. 4). Pigeons can respond not only to the frequency of a stimulus, but also to its intensity. The interval decrement (in %) of ECG is a positive correlative function of the stimulus intensity, the calculated values being approximately 4–5% per order of magnitude of the stimulus amplitude (in m) at best frequencies (Fig. 5). The value of vibration detection for birds is discussed.Abbreviation ECG electrocardiogram     

Visual contributions to human self-motion perception during horizontal body rotation

It is still an enigma how human subjects combine visual and vestibular inputs for their self-motion perception. Visual cues have the benefit of high spatial resolution but entail the danger of self motion illusions. We performed psychophysical experiments (verbal estimates as well as pointer indications of perceived self-motion in space) in normal subjects (Ns) and patients with loss of vestibular function (Ps). Subjects were presented with horizontal sinusoidal rotations of an optokinetic pattern (OKP) alone (visual stimulus; 0.025-3.2 Hz; displacement amplitude, 8 degrees) or in combinations with rotations of a Bárány chair (vestibular stimulus; 0.025-0.4 Hz; +/- 8 degrees). We found that specific instructions to the subjects created different perceptual states in which their self-motion perception essentially reflected three processing steps during pure visual stimulation: i) When Ns were primed by a procedure based on induced motion and then they estimated perceived self-rotation upon pure optokinetic stimulation (circular vection, CV), the CV has a gain close to unity up to frequencies of almost 0.8 Hz, followed by a sharp decrease at higher frequencies (i.e., characteristics resembling those of the optokinetic reflex, OKR, and of smooth pursuit, SP). ii) When Ns were instructed to "stare through" the optokinetic pattern, CV was absent at high frequency, but increasingly developed as frequency was decreased below 0.1 Hz. iii) When Ns "looked at" the optokinetic pattern (accurately tracked it with their eyes) CV was usually absent, even at low frequency. CV in Ps showed similar dynamics as in Ns in condition i), independently of the instruction. During vestibular stimulation, self-motion perception in Ns fell from a maximum at 0.4 Hz to zero at 0.025 Hz. When vestibular stimulation was combined with visual stimulation while Ns "stared through" OKP, perception at low frequencies became modulated in magnitude. When Ns "looked" at OKP, this modulation was reduced, apart from the synergistic stimulus combination (OKP stationary) where magnitude was similar as during "staring". The obtained gain and phase curves of the perception were incompatible with linear systems prediction. We therefore describe the present findings by a non-linear dynamic model in which the visual input is processed in three steps: i) It shows dynamics similar to those of OKR and SP; ii) it is shaped to complement the vestibular dynamics and is fused with a vestibular signal by linear summation; and iii) it can be suppressed by a visual-vestibular conflict mechanism when the visual scene is moving in space. Finally, an important element of the model is a velocity threshold of about 1.2 degrees/s which is instrumental in maintaining perceptual stability and in explaining the observed dynamics of perception. We conclude from the experimental and theoretical evidence that self-motion perception normally is related to the visual scene as a reference, while the vestibular input is used to check the kinematic state of the scene; if the scene appears to move, the visual signal becomes suppressed and perception is based on the vestibular cue.     

Spectral-correlative characteristics of the EEG reactions preceding conditioned reflex motor reactions in dogs

The work is a logical continuation of previous studies (analysis of the background electrical activity in the band 1-100 Hz in interstimulus intervals in the process of lever pressing alimentary conditioning in dogs) and it is dedicated to correlation-spectral analysis of prestimulus periods and EEG-reactions to conditioned stimuli, previous to conditioned lever pressing. Visually the EEG reactions present discharges of high-frequency (40-100 Hz) synchronized activity preceding for 40-300 ms the beginning of the changes in EMG of the "working" limb. It is shown that EEG reactions are characterized (in comparison with the background activity) by a higher energetic level and a greater expression of the high coherence (I greater than 0.75) and also by greater phase shifts, in counterbalance to the domination of little phase shifts in the background activity. It is assumed that the patterns of EEG reactions may participate in trigger mechanisms either eliciting conditioned motor reactions (to positive conditioned stimuli) or preventing them (to inhibitory conditioned stimuli).     

Oscillatory synchrony and human visual cognition.

Oscillatory synchrony could be used to establish dynamic links between the various cortical areas participating in the same cognitive process. Is it possible to detect oscillatory synchrony in humans, and is it relevant to behavior? There is now converging evidence for the existence of a transient oscillatory activity in the gamma range (30-60 Hz), obtained in response to static visual objects, and having only a loose temporal relationship to stimulus onset. This so-called "induced" gamma response is much larger in response to coherent static or moving objects. However, functional variations of gamma and/or beta (15-20 Hz) oscillations are not restricted to perceptive, bottom-up mechanisms, but are also observed during visual imagery or short-term memory maintenance. Oscillations at the scalp level thus seem to reflect large-scale neural cooperativity in a variety of task-dependent networks. Human intra-cranial recordings in a short-term memory paradigm further reveal the existence and the task-dependency of oscillatory synchrony in the beta range, between focal sites separated by several centimeters and with a few milliseconds time-lag. These findings thus confirm experimentally the hypothesis of a functional role of synchronized oscillatory activity in the coordination of distributed neural activity in humans, and support Hebb's concept of short-term memory maintenance by reentrant activity within the activated network. In addition, the intra-cranial data obtained in humans and monkeys also help to better understand the neural mechanisms generating scalp-recorded oscillations.     

Towards a unified model of pavlovian conditioning: short review of trace conditioning models

There are three basic paradigms of classical conditioning: delay, trace and context conditioning where presentation of a conditioned stimulus (CS) or a context typically predicts an unconditioned stimulus (US). In delay conditioning CS and US normally coterminate, whereas in trace conditioning an interval of time exists between CS termination and US onset. The modeling of trace conditioning is a rather difficult computational problem and is a challenge to the behavior and connectionist approaches mainly due to a time gap between CS and US. To account for trace conditioning, Pavlov (Conditioned reflexes: an investigation of the physiological activity of the cerebral cortex, Oxford University Press, London, 1927) postulated the existence of a stimulus “trace” in the nervous system. Meanwhile, there exist many other options for solving this association problem. There are several excellent reviews of computational models of classical conditioning but none has thus far been devoted to trace conditioning. Eight representative models of trace conditioning aimed at building a prospective model are being reviewed below in a brief form. As a result, one of them, comprising the most important features of its predecessors, can be suggested as a real candidate for a unified model of trace conditioning.     

Several mechanisms of acetylcholine participation in the processes of formation and fixation of temporary connections

Microphoretic application of acetylcholine (ACH) to the neurones of the rabbit sensorimotor cortex elicits changes of spontaneous and evoked activity which do not correlate with one another and which persist up to two minutes after the end of ACH application. Following the formation of a defensive conditioned reflex to sound, the reactions to ACH in units involved in the formation of the temporary connection are intensified as compared with their reactions before conditioning and with reactions of those neurones which did not elaborate a temporary connection. The possible mechanisms of ACH participation in the processes of elaboration and fixation of temporary connections are discussed.     

Gamma oscillations in human primary somatosensory cortex reflect pain perception

Successful behavior requires selection and preferred processing of relevant sensory information. The cortical representation of relevant sensory information has been related to neuronal oscillations in the gamma frequency band. Pain is of invariably high behavioral relevance and, thus, nociceptive stimuli receive preferred processing. Here, by using magnetoencephalography, we show that selective nociceptive stimuli induce gamma oscillations between 60 and 95 Hz in primary somatosensory cortex. Amplitudes of pain-induced gamma oscillations vary with objective stimulus intensity and subjective pain intensity. However, around pain threshold, perceived stimuli yielded stronger gamma oscillations than unperceived stimuli of equal stimulus intensity. These results show that pain induces gamma oscillations in primary somatosensory cortex that are particularly related to the subjective perception of pain. Our findings support the hypothesis that gamma oscillations are related to the internal representation of behaviorally relevant stimuli that should receive preferred processing.     

Effects of high-frequency skin stimulation on SI cortex: mechanisms and functional implications

Optical intrinsic signal (OIS) imaging methods were used to record the responses of contralateral SI cortex to 25 Hz ("flutter") and also to 200 Hz ("vibration") stimulation of the skin. Anesthetized cats and squirrel monkeys were subjects. Separate series of experiments were carried out to evaluate the contralateral SI response to continuous, multisecond 25 Hz vs. 200 Hz stimulation (a) at multiple skin sites arranged along the proximal-distal axis of the fore- or hindlimb (Series I); (b) in the presence and absence of a ring placed in firm contact with the skin surrounding the stimulus site (Series II); (c) before and after topical application of local anesthetic to the stimulus site (Series III); and, finally, (c) to continuous 25 Hz or 200 Hz stimulation applied independently, and also concomitantly ("complex waveform stimulation") to the same skin site (Series IV). The principal findings are: (a) the relationship between the SI optical responses to 25 Hz vs. 200 Hz stimulation of a skin site varies systematically with position of the stimulus site on the limb-at a distal site both 25 Hz and 200 Hz stimulation evoke a well-maintained increase in absorbance, and as the stimulus site is shifted proximally on the limb the response to 200 Hz, but not the response to 25 Hz stimulation, converts to a frank decrease in absorbance; (b) placement of a ring about a skin site at which in the absence of a ring 200 Hz stimulation evoked a decrease in SI absorbance converts the response to 200 Hz to one consistent with increased SI RA neuronal activation (i.e., with the ring in place 200 Hz stimulation evokes a change in SI absorbance approximating the response to 25 Hz stimulation); (c) topical local anesthetic preferentially and reversibly decreases the magnitude of the absorbance increase associated with 25 Hz flutter stimulation; and (d) complex waveform stimulation consistently is associated with a smaller increase in absorbance than obtained with same-site 25 Hz stimulation. Collectively, the findings are consistent with the idea that the Pacinian (PC) afferent activity which unavoidably accompanies cutaneous flutter stimulation triggers CNS mechanisms that "funnel" (sharpen) the spatially distributed contralateral SI response to the flutter stimulus. Viewed in this context, the fact that a flutter stimulus unavoidably co-activates RA and PC afferents appears functionally beneficial because the CNS mechanisms activated by PC afferent drive modify the SI response to skin flutter in a manner predicted to enable more accurate perceptual localization than would be possible if the flutter stimulus only activated RA afferents.     

Linear Tuning of Gamma Amplitude and Frequency to Luminance Contrast: Evidence from a Continuous Mapping Paradigm

Individual differences in the visual gamma (30–100Hz) response and their potential as trait markers of underlying physiology (particularly related to GABAergic inhibition) have become a matter of increasing interest in recent years. There is growing evidence, however, that properties of the gamma response (e.g., its amplitude and frequency) are highly stimulus dependent, and that individual differences in the gamma response may reflect individual differences in the stimulus tuning functions of gamma oscillations. Here, we measured the tuning functions of gamma amplitude and frequency to luminance contrast in eighteen participants using MEG. We used a grating stimulus in which stimulus contrast was modulated continuously over time. We found that both gamma amplitude and frequency were linearly modulated by stimulus contrast, but that the gain of this modulation (as reflected in the linear gradient) varied across individuals. We additionally observed a stimulus-induced response in the beta frequency range (10–25Hz), but neither the amplitude nor the frequency of this response was consistently modulated by the stimulus over time. Importantly, we did not find a correlation between the gain of the gamma-band amplitude and frequency tuning functions across individuals, suggesting that these may be independent traits driven by distinct neurophysiological processes.     

Increased regularity of activity of cortical neurons in learning due to disinhibitory effect of reinforcement

This paper reviews the author's studies on neurophysiologic mechanisms of conditioned reflex learning. Electroencephalograms, evoked potentials, activity of neocortical and hippocampal neurons and the rabbits' behavior in the course of elaboration of defensive and inhibitory conditioned reflexes to light flashes have been recorded. Electric shock (ECS) applied to the paw served as reinforcement. The study demonstrated three types of reinforcement effect on the activity of cortical neurons: activating, disinhibitory, and inhibitory. EEG activation due to reinforcement is accompanied by a change in phasic cortical neuronal activity from chaotic or irregular, typical of rest or inhibition, to regular tonic discharges (in neocortex and hippocampus) and group discharges in the stress rhythm, 5-7 Hz in the hippocampus. Following a number of conditioning trials, the effect of reinforcement is simulated by the effect of a conditioned stimulus. With EEG activation and increased regularity in impulses, facilitation of motor reactions is observed.     

Vibrational sensitivity of the wing of the pigeon (Columba livia) — a study using heart rate conditioning

Summary The vibrational sensitivity of awake pigeons was tested with the heart rate conditioning method. This method proved to be a very sensitive instrument for the behavioural measurement of the pigeon's sensitivity to mechanical stimuli.Sine wave vibrational stimuli between 50 and 2000 Hz were applied to the 1st, 7th and 16th primary feathers of the wing. The resulting threshold curves were U- or V-shaped with 3 characteristics: (i) The frequency of best response was either 800 or 900 Hz. (ii) Within the broad frequency range of vibrational sensitivity (50 to 2000 Hz) the sensitivity was extremely high at the best frequency: threshold amplitudes lay between 0.5 and 0.09 m. (iii) The threshold curves showed very sharp tuning at best frequency with bandwidths between 0.3 and 0.7 octaves (measured at best frequency 10fold above threshold). The functional meaning of the characteristic vibrational sensitivity of the wing for flight control is discussed; it is interpreted as an adaptation to special situations occurring during flight.Abbreviations CR conditioned response - CS conditioned stimulus - ECG electrocardiogram - HC(s) Herbst corpuscle(s) - UCS unconditioned stimulus All experiments were carried out at the Ruhr-Universität Bochum, Lehrstuhl für Allgemeine Zoologie     

Perception of the tactile texture of raised-dot patterns: a multidimensional analysis

An ALSCAL multidimensional scaling analysis in Euclidean space revealed that three orthogonal perceptual dimensions can account for the judged tactile dissimilarities of raised-dot patterns. Through magnitude estimates of various perceptual attributes, it was determined that the three dimensions consist of blur, roughness, and clarity. The only effect that selective adaptation of the Pacinian (P) channel had was to change the perceptual clarity of the raised dots against their background. Adaptation of the P channel with a 20 dB SL 250 Hz stimulus enhanced clarity. As indicated by magnitude estimates, adaptation of the P channel by the 250 Hz stimulus had no effect on the perceived roughness of the dot pattern but did cause the individual dots of the textured pattern to feel smoother. When the observer was required to estimate magnitude "overall roughness" defined as a combination of dot-pattern roughness and individual-dot roughness, adaptation of the P channel affected perceived roughness by reducing it. Taken as a whole, the results are consistent with the hypothesis that the NP channels and the P channel jointly influence the perception of textured surfaces.