2nd Stimulus Research Articles

Collinear facilitation: Effect of additive and multiplicative external noise

The detectability of a Gabor patch is improved by the presence of collinear flanking Gabors, this phenomenon is termed collinear facilitation. In experiment 1, we investigate the effects of adding 2D spatial luminance noise as a means of investigating different transects through the suprathreshold contrast space to see whether facilitation is ubiquitous throughout the contrast domain or whether it is confined to absolute contrast threshold. The results show that adding luminance noise abolishes the facilitation, showing it is confined to absolute threshold. In experiment 2, we assess whether 2nd order stimuli exhibit collinear facilitation and whether 1st order flanks can induce facilitation in 2nd order stimuli and vice versa. Our results suggest that collinear facilitation, albeit weaker, does occur for some 2nd order stimuli but we did not find any 1st/2nd order interactions, suggesting separate 1st/2nd order cortical processing streams, at least at the level at which this phenomenon occurs. Our two main findings, namely the lack of facilitation at suprathreshold contrasts and its presence for 2nd order processing argue against it playing a pivotal role in contour integration which does occur at all contrasts but not for these 2nd order stimuli.

Temporal generalization and peak shift in humans

Three experiments investigated temporal generalization in humans. In Experiment 1, a peak shift effect was produced when participants were given intradimensional discrimination training. In Experiment 2, after training with a standard S+ and generalization testing with an asymmetrical series of durations, generalization gradients moved toward the prevailing adaptation level. In Experiment 3, generalization gradients showed acentral tendency shift and moved away from the S+ and toward the mean of the test series (of 11 stimulus durations) after participants received training with S+ and S- durations that in one condition were the 2nd and 4th and in another condition were the 4th and 2nd stimuli in the series, respectively. The results were inconsistent with an absolute account of peak shift but were consistent with an adaptation level account of peak shift.

Action planning in the presence of distracting stimuli: An investigation into the time course of distractor effects.

Humans have a remarkable capability to respond efficiently to a stimulus of interest despite other stimuli competing for neural resources. The current study investigated how the human system copes with distracting stimuli. During each trial, participants viewed 2 sequential stimuli that were each associated with a specific action based on an arbitrary mapping. The 1st stimulus served as a distractor, and the 2nd stimulus required a response (target). When the distractor preceded the target by more than a few hundred milliseconds, response latencies were slower when the 2 stimuli were associated with the same response. The authors propose that this negative compatibility effect stemmed from an inhibitory mechanism that the human system utilizes to prevent the distractor from eliciting an unwanted response.

Neuronal responses to a delayed-response delayed-reward go/nogo task in the monkey posterior insular cortex

Anatomical connections of the insular cortex suggest its involvement in cognition, emotion, memory, and behavioral manifestation. However, there have been few neurophysiological studies on the insular cortex in primates, in relation to such higher cognitive functions. In the present study, neural activity was recorded from the monkey insular cortex during performance of a delayed-response delayed-reward go/nogo task. In this task, visual stimuli indicating go or nogo responses associated with reward (reward trials) and with no reward (no-reward trials) were presented after eye fixation. In the reward trials, the monkey was required to release a button during presentation of the 2nd visual stimuli after a delay period (delay 1). Then, a juice reward was delivered after another delay (delay 2). The results indicated that the neurons responding in each epoch of the task were topographically localized within the insular cortex, consistent with the previous anatomical studies indicating topographical distributions of afferent inputs from other subcortical and cortical sensory areas. Furthermore, some insular neurons 1) nonspecifically responded to the visual cues and during fixation; 2) responded to the visual cues predicting reward and during the delay period before reward delivery; 3) responded differentially in go/nogo trials during the delay 2; and 4) responded around button manipulation. The observed patterns of insular-neuron responses and the correspondence of their topographical localization to those in previous anatomical studies suggest that the insular cortex is involved in attention- and reward-related functions and might monitor and integrate activities of other brain regions during cognition and behavioral manifestation.

Short-term habituation of the intracranially recorded auditory evoked potentials P50 and N100

At an interstimulus interval (ISI) of 500-ms stimulus repetition leads to a strong decrease in cortical response. The functional foundation of this response suppression (or sensory gating) is yet not fully understood. Experiments on short-term habituation using the same stimulus material as sensory gating experiments and same ISI might help to elucidate the mechanisms behind the P50 suppression. Event-related potentials were recorded intracranially in epileptic patients undergoing presurgical evaluation with subdural and depth electrodes. Stimulus material consisted of trains of six clicks, with the last stimulus deviating in pitch and duration. P50 and N100 were calculated for each stimulus in the train separately and compared by analysis of variance (ANOVA). A highly significant amplitude reduction was found from the 1st to 2nd stimulus for both P50 and N100. From the 2nd to 5th stimulus no further amplitude decrease was observable. The deviating 6th stimulus led to a response recovery of both components, but the P50 elicited by the 6th stimulus was still smaller than the P50 of the 1st stimulus. Current results indicate that the P50 suppression as investigated in sensory gating experiments seems to be completed after the 2nd stimulus.

Aging and input processing in dual-task situations.

The psychological refractory period (PRP) paradigm was used to test whether older participants suffer from input interference in dual-task situations. Young (24 years) and older (57 years) adults gave speeded responses to 2 successively presented stimuli. The results showed increased susceptibility of older participants to input interference. Further experiments revealed that this input interference is related to the salience of the 2nd stimulus and that it is specific to older participants. Our findings indicate that parallel processing at the input stages of dual-task performance requires cognitive control. An age-related decline in the control of input processes should be considered as one source of age effects in dual-task performance.

ラットの視覚刺激と聴覚刺激の短期記憶に及ぼす抗コリン作動薬投与と内側中隔破壊の効果

This study examined the effects of administration of anticholinergic drugs and medial septum lesion on the performance of the successive delayed matching-to-sample (S-DMTS) task in rats in order to clarify the relationship between the central cholinergic system and the modality effect in rats' short-term memory. A pair of visual and/or auditory stimuli was presented with delay intervals to rats. They were required to distinguish whether the modality of the 2nd stimulus (S2) for the pair was the identical to or different from that of the 1st stimulus (S1). Scopolamine at 0.03-0.1mg/kg (i. p.) and mecamylamine at 1-3mg/kg (i. p.) disrupted the performance of S-DMTS task irrespective of the modality of S1, whereas methyl-scopolamine and hexamethonium did not. These results suggest that muscarinic and nicotinic receptors in rats' brain are correlated with short-term memory for both visual and auditory stimuli. Lesion to medial septum also disrupted the performance of S-DMTS task when the visual stimulus was presented as S1, however, the performance was not changed when the auditory stimulus was employed. These findings suggest that the medial septum is correlated with the mnemonic processes of visual but not of auditory stimuli.

Involvement of the rat medial prefrontal cortex in novelty detection.

The prefrontal cortex in humans has been implicated in processes that underlie novelty detection and attention. This study examined the contribution of the rat medial prefrontal cortex to novelty detection using the targeting, or orienting, response (OR) as a behavioral index. Lesions to the medial prefrontal cortex (specifically the prelimbic and infralimbic cortices) influenced neither the OR to a novel visual stimulus from a localized light source (V1), nor the change in this OR over the course of a series of exposures to V1. However, after exposure to V1, the OR to a 2nd visual stimulus from the same source, V2, was more pronounced in control rats than in lesioned rats. These results suggest that the medial prefrontal cortex in the rat contributes to the process of novelty detection.

Parallel memory retrieval in dual-task situations: II. Episodic memory.

Three experiments asked whether subjects could retrieve information from a 2nd stimulus while they retrieved information from a 1st stimulus. Subjects performed recognition judgments on each of 2 words that followed each other by 0, 250, and 1,000 ms (Experiment 1) or 0 and 300 ms (Experiments 2 and 3). In each experiment, reaction time to both stimuli was faster when the 2 stimuli were both targets (on the study list) or both lures (not on the study list) than when 1 was a target and the other was a lure. Each experiment found priming from the 2nd stimulus to the 1st when both stimuli were targets. Reaction time to the 1st stimulus was faster when the 2 targets came from the same memory structure at study (columns in Experiment 1; pairs in Experiment 2; sentences in Experiment 3) than when they came from different structures. This priming is inconsistent with discrete serial retrieval and consistent with parallel retrieval.

Parallel memory retrieval in dual-task situations: I. Semantic memory.

Can participants retrieve information about the 2nd of 2 stimuli while they are processing the 1st? Four experiments suggest they can. Reaction times to the 1st stimulus were faster if it came from the same category as the 2nd than if it came from a different category. This category-match effect was observed for letter-digit discrimination (Experiment 1), magnitude and parity judgments about digits (Experiment 2), and lexical decisions (Experiment 3). Experiment 4 showed that the 2nd stimulus could semantically prime the 1st. The category-match effect was observed only when the same task was performed on the 2 stimuli. When the task changed from the 1st stimulus to the 2nd, there was no advantage of a category match. This dependence on task set may explain previous failures to find parallel retrieval.

Relationship between Responses to Contra- and Ipsilateral Stimuli in the Human Second Somatosensory Cortex SII

We studied the interaction between responses to contra- and ipsilateral stimuli in the human second somatosensory cortex SII by recording somatosensory evoked magnetic fields (SEFs) from 8 healthy subjects with a 122-channel whole-scalp SQUID magnetometer. Right (R) and left (L) median nerves were electrically stimulated at the wrists at intensities exceeding the motor threshold. In each stimulus sequence, the four equiprobable pairs (L-L, R-R, L-R, R-L) were presented in a random order once every 2 s, with a 300-ms interstimulus interval within the pair. The responses were modelled with a four-dipole model, with current dipoles located in the SI and SII cortices of both hemispheres. The SII responses peaked around 85–120 ms and responses to the 1st (2nd) stimulus on the pair were on average 2 (12) ms earlier and about 3 (2.5) times stronger for contralateral than ipsilateral stimuli. Independently of the condition, the 2nd response always peaked later than the 1st; the mean delay was 16 ms. The responses to the 2nd stimulus depended only slightly on the type of the 1st: the latency increased more and the amplitude decreased less after different than identical 1st stimuli. These results suggest that neuronal activations due to contra- and ipsilateral stimuli overlap strongly in the human SII cortex.

Indications for coupling between feline spinocervical tract neurones and midlumbar interneurones.

The possibility of collateral segmental actions of spinocervical tract (SCT) neurones upon interneurones with input from cutaneous and group II muscle afferents was investigated in deeply anaesthetized cats. To this end, intracellular and/or extracellular recordings were made from 35 dorsal horn and 15 intermediate zone interneurones in midlumbar segments of the spinal cord and effects of stimulation of the ipsilateral dorso-lateral funiculus (DLF) at C3 and C1 levels, i.e. below and above the lateral cervical nucleus where axons of SCT cells terminate, were compared. The stimuli applied at the C3 segment were within the range of stimuli (50-100 microA) required for antidromic activation of SCT neurones in the same experiment. Those applied at the C segment (200-500 microA) were at least 3 times stronger than C3 stimuli. Under the same experimental conditions, long ascending and descending tract neurones (dorsal spino-cerebellar and rubro-spinal tract neurones) with axons in the DLF were activated at similar thresholds from the C and C3 segments. Intracellular recordings were made from 29 interneurones of which 19 (65%) were dorsal horn and 10 (35%) were intermediate zone interneurones. Excitatory postsynaptic potentials (EPSPs) evoked by single stimuli applied at the C3 segment, but not the C segment, were found in 14 (48%) of those interneurones; their latencies (3.0-5.7 ms) and frequency following with only minimal temporal facilitation were as required for potentials being evoked monosynaptically by the fastest conducting SCT neurones. Extracellular recordings were made from 30 interneurones (24 dorsal horn and 6 intermediate zone interneurones), and in these neurones spike potentials induced from the C3, but not from the C segment, were evoked only by short trains of stimuli. However, their latencies from the first effective stimulus (4.3-5.4 ms) were compatible with mono- or oligosynaptically mediated collateral actions of SCT neurones. They were found in 10 (33%) of the 30 investigated interneurones. Similar effects of C3 stimuli were found in similar proportions of dorsal horn interneurones and intermediate zone interneurones. Indications were also found for synaptic actions evoked by C3 stimuli that could not be attributed to direct collateral actions of SCT neurones. In some intracellularly recorded dorsal horn interneurones, short-latency EPSPs were evoked from the C3 segment by the 2nd or 3rd stimulus in the train, but not by single stimuli. In other dorsal horn and intermediate zone interneurones, inhibitory postsynaptic potentials (IPSPs) were evoked from the C3 segment at minimal latencies (2.7-3.2 ms), which might be too short to allow their mediation via SCT neurones. We conclude that SCT neurones might be used to forward information from muscle group II and cutaneous afferents not only to neurones in the lateral cervical nucleus and via them to thalamus and cerebral cortex but also to interneurones in spinal reflex pathways. Thereby reflex actions evoked from group II and cutaneous afferents might be co-ordinated with responses mediated by supraspinal neurones. We conclude also that dorsal horn and intermediate zone mid-lumbar interneurones might contribute to the previously reported di-and poly-synaptic excitation or inhibition of postsynaptic dorsal column (PSDC), spinothalamic tract (STT) and spinomesencephalic tract (SMT) neurones by collateral actions of SCT cells. Thereby these interneurones might contribute to the co-ordination of responses mediated by various populations of supraspinal neurones.

Mistaken Identity: Temporal-Order Biases in the Perception of Speed

Biases in the perceived speed of a moving stimulus have been observed for various spatial configurations of a motion stimulus (eg Norman et al, 1996 Perception25 815 – 830). In general, psychophysical studies are designed to remove any possible source of bias due to the temporal order of presentation. Here, we examined biases in speed perception between the first and second temporal interval in a 2IFC procedure. The stimulus was a circular patch (∼ 2 deg) containing 50 translating dots. A standard speed was always presented in the first interval (∼ 6 deg s−1), with one of 7 test speeds in the second interval. A range of ISIs (0 – 2.3 s) and stimulus durations (100 – 900 ms) was tested. We also dissociated spatial location (left/right of fixation point) and direction of dot travel (left/right and vertical/horizontal) of the two stimuli, whilst maintaining the temporal separation. In all cases we found an increase in perceived speed from 1st to 2nd interval and further, the effect was independent of direction, ISI, duration, and the spatial position of the 1st and 2nd stimuli. We can suggest no simple account of the results based upon neural fatigue in motion detectors, temporal sampling windows, or representational momentum. Tentative models are currently being explored with three interval stimuli.

Effects of spinal cord ischemia on the refractory period of descending spinal cord evoked potential

The recovery cycle, following the conduction of action potentials along a nerve fiber, consists of the absolute refractory period (ARP), the relative refractory period (RRP) and the supernormal period (SNP). The recovery cycle of the descending conductive spinal cord evoked potential (SCEP) was shown during normal state, ischemia and after ischemia using paired stimuli in cats. During ischemia the refractory period revealed a trend towards increment. Five minutes after reperfusion the refractory period decreased transiently compared with the normal level and within 30 min the refractory period returned to the normal level. The recovery curve of the 2nd potential showed different pattern compared with that of the 1st potential. Moreover, during ischemia, firstly the 3rd potential and secondly the 2nd potential of the SCEP elicited by the 2nd stimulus were disturbed. These results demonstrated that there is increased excitability of the spinal cord to the second stimulus after a brief period of ischemia, and that the 2nd and 3rd potentials are evoked synaptically and easily disturbed during ischemia. Measuring the SCEP elicited by paired stimuli or constructing the recovery curve of the SCEP is useful for the electrophysiological assessment of spinal cord function.

Discriminative inhibition is specific to the response-reinforcer association but not to the discriminative stimulus.

In 4 experiments an instrumental contingency between a response and a reinforcer was introduced in the presence of a discriminative stimulus. Then a discriminative inhibitor (S delta) was established that signaled that the instrumental contingency would no longer operate in the presence of that discriminative stimulus, so that the S delta suppressed operant responding. The degree to which the S delta, s inhibitory properties transferred to different discriminative stimuli and different response-reinforcer associations was then explored. In Experiments 1 and 2 the S delta, s effects transferred perfectly to a 2nd discriminative stimulus, whereas the results of Experiments 3 and 4 were consistent with the hypothesis that the S delta, s inhibitory properties were specific to the original response-reinforcer association. The theoretical implications of these findings are discussed.

How To Hunt for Hiding Hosts: the Reliability-Detectability Problem in Foraging Parasitoids

Foraging parasitoids may use stimuli that are derived from their host or from the food of their host, often plants. But how usable are 2nd and 1st trophic level stimuli and what is their relative importance in parasitoid foraging? It is argued that foraging parasitoids are facing a reliability-detectability problem: host-derived stimuli are the most reliable in indicating host presence, accessibility and suitability but they are generally hard to detect. Plant stimuli, on the other hand, are easier to detect but arc generally less reliable indicators. Parasitoids have evolved different non-exclusive strategies to solve this problem. (1) Infochemical detour: parasitoids resort to information from other, more detectable, host stages than the one under attack. (2) Herbivore-induced synomones: parasitoids use specific plant produced volatiles that are released upon damage by a specific herbivore species. In the present paper we put most emphasis on a third strategy (3) Associative learning: through associative learning parasitoids link easy-to-detect stimuli to reliable but hard-to-detect stimuli. Specific mechanisms by which associative learning can improve foraging success are discussed.

Progesterone alters the pituitary response to luteinizing hormone releasing hormone in postmenopausal women previously treated with estradiol

The effect of luteinizing hormone-releasing hormone (LHRH) on LH release was studied in 5 menopausal women injected with progesterone. Each patient received 2 x 100 micrograms doses of LHRH administered intravenously 120 minutes apart under the following conditions: without any previous treatment (test 1); 16 hours after intramuscular injection of 10 mg progesterone (test 2); after 3-4 weeks of oral treatment with 50 micrograms/day of ethinyl estradiol (EE2) (test 3); 16 hours after intramuscular injection of 10 mg progesterone following treatment with 50 micrograms/day oral EE2 for 3-4 weeks (test 4). The interval between tests was at least 1 month. Progesterone decreased the total plasma hormonal increment (PHIt) of hypogonadal women, with a reduction in plasma hormonal increment both after the 1st stimulus (PHI1) and after the 2nd stimulus (PHI2), whereas estradiol increased PHIt, mainly due to an increase of PHI2. The administration of progesterone to hypogonadal women previously treated with EE2 maintained the increased PHIt caused by the latter, but not owing to a greater increase in PHI1.

Thalamocortical and intrathalamic interactions during slow repetitive stimulation of n. centralis lateralis.

Extracellular single unit activity was recorded simultaneously in cortex (anterior part of the middle suprasylvian gyrus, MSSG) and thalamus (n. ventralis anterior, VA; n. lateralis posterior, LP) during repetitive low frequency stimulation (RLFS) of n. centralis lateralis (CL) in lightly anesthetized cats. Such stimulation induced typical recruiting responses in the cortical EEG consisting of long-latency, surface-negative waves reversing in polarity at 0.1-2mm depth. These cortical EEG responses were associated with long-latency (8-20 ms) action potential (AP) discharges of cortical neurons appearing with the 2nd stimulus of the train. The number of AP discharges and response latency increased as the train of CL stimuli progressed. In 12 of these neurons there was a short-latency (up to 2-5 ms) response which, however, did not show incremental features during RLFS. Thalamic neurons in VA usually responded to the first stimulus within a train of RLFS of CL, while LP neurons responded only to the 2nd or 3rd stimulus. Peristimulus time histograms (PSTHs) of AP discharges in VA showed an increase in both number and latency of APs as the train of stimuli progressed. This was also observed in those thalamic neurons in LP which changed their firing during RLFS of CL. The peak of firing of 20 VA neurons preceded, and that of 7 followed that of the MSSG neurons, while 6 VA and MSSG neuronal pairs reached their peak firing simultaneous; peak firing of 29 LP neurons preceded, and that of 21 followed the firing peak of MSSG neurons. The thresholds of the incremental responses of MSSG, VA and LP neurons to progressively increased intensity of RLFS of CL were different: MSSG and VA neurons changed their firing pattern at an intensity incapable of modifying the activity of LP neurons. When stimulation intensity was increased to a level sufficient to change the responses of both neurons of a given pair (either MSSG-VA or MSSG-LP) the time sequence of involvement in the incremental process was in the following order: VA, MSSG, LP. Within a range of RLFS extending from 2-20 Hz, stimulation at 6.6 Hz (150 ms interstimulus intervals) induced the most prominent incremental responses both in the cortex and thalamus, i.e. response increases were largest when each subsequent stimulus occurred 50-130 ms before the expected rebound excitation following the preceding response.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of sodium nitrite on the action potential responses of the ventricular muscles of mice

The effects of sodium nitrite (NaNO2) were tested on strips of the cardiac muscle prepared from the ventricles of male ICR mice 4, 16 and 78 week-old. The strips were immersed in Ringer solution containing 0.01% NaNO2 and action potentials evoked by repetitive electrical stimulation were recorded by means of conventional microelectrode recording. The results obtained were as follows.1) In 4 week-old mice: No detectable difference was observed in the action potential responses evoked by 5Hz stimulation at 1.3V in the control (before treatment), treatment (with NaNO2) and recovery periods. At 10Hz, action potentials were evoked once every 2 stimuli in the control and once every stimuli in the treatment. At 20Hz, action potentials were evoked every 3rd stimulus in the control and once every 2nd stimulus in the treatment. The responses thus elevated did not return to the control level during the periods of recovery after wash out of the drug.2) In 16 week-old mice: The responses were tested at 1.0V and found similar to that of the 4 week-old animals. However, they recovered appreciably during the wash out period.3) In 78 week-old mice: Action potentials were normally evoked by 1.5V stimuli at 5Hz in the same way as 1) and 2), whereas 2.8V were needed at 10 and 20Hz in the treatment with the drug. The responses was elevated in the treatment, as in 1) and 2), and somewhat reduced in the wash out period.

End-plate currents evoked by paired stimuli in frog muscle fibres.

Using voltage-clamp techniques spontaneously occurring miniature end-plate currents (mepc) and nerve-evoked end-plate currents (epc) were recorded in frog glycerol-treated or cut muscle preparations. Epcs were induced by pairs of stimuli (the delay of the 2nd stimulus, delta t being 6 ms-30 s; one pair was delivered every 60-90 s). The decay time constant of the epc (tau epc) was longer, the larger its quantal content despite the presence of active acetylcholinesterase (AChE). After treatment with anticholinesterases (prostigmine or armin, an irreversible inhibitor) this increase in tau epc became more pronounced. When AChE was fully active the decay of the 1st epc (tau 1) was slightly faster than the decay of the 2nd epc (tau 2) only when the interstimulus interval was rather short (delta t less than 20 ms). Following treatment with anticholinesterases this difference between tau 2 and tau 1 could be determined even when delta t was as long as 30 s. In anticholinesterase-treated preparations delta tau was found to be inversely proportional to log delta t: a 50% increase in the decay time-constant of the 2nd epc occurred with delta t = 120 ms. During continuous stimulation (10 impulses/s) tau epc increased from the 1st to the 5-6th responses, but then decreased in parallel with the fall in the epc amplitude. The phenomenon of postsynaptic potentiation we observed could be readily abolished when quantal content was decreased by the presence of magnesium ions, but it was relatively unaffected when the receptor density was decreased by alpha-bungarotoxin (alpha-BuTX).(ABSTRACT TRUNCATED AT 250 WORDS)