Individual differences in infant orienting and autonomic conditioning

Conditioned discrimination and discrimination reversal of the skin potential response was attempted and subsequently demonstrated in 3-month-old infants. Analysis of individual subject data indicated individual differences in conditionability, as well as a significant relation between orienting response magnitude and conditionability. In general, high-magnitude orienters discriminated; low-magnitude orienters did not. Behavioral ratings of state, sex of subject, and stimulus order were not related to orienting or to conditionability.     

Rabbit eyelid conditioning: Effects of age,interstimulus interval,and intertrial interval

Young rabbits (5–7 weeks old) conditioned more rapidly and demonstrated longer latency responses than older rabbits (14–20 weeks old) with an 800-msec interstimulus interval. With a 200- or 400-msec interval, conditioning rate and response latency were similar for both age groups. Although a 4-min intertrial interval produced conditioning in fewer trials than a 1-min interval, there was no interaction of this variable with the age factor.     

Orienting reactions, expectancy learning, and conditioned responses in electrodermal conditioning with different interstimulus intervals

The aim of this study was to evaluate the processes of orienting, expectancy learning, and CR acquisition in GSR conditioning with interstimulus intervals of 0.5, 4.0 and 8.0 sec. By comparing groups of subjects given CS and UCS paired (conditioning) with groups given CS paired with a non-aversive stimulus (expectancy learning), the effect of CR acquisition should be observable, and by comparing the expectancy learning groups with groups given unpaired stimulus presentations (orienting), it should be possible to assess the effect of expectancy. The results supported the operation of orienting and CR acquisition processes at all interstimulus intervals studied. For the expectancy learning process, there seemed to be a distinction between a component reflecting the learning of the stimulus contingency, which was observable at all interstimulus intervals, and an anticipatory component, that could be observed in the conditioning groups at the two longer intervals.     

P300, Probability, and Interstimulus Interval

The relationship between target stimulus probability and interstimulus interval on the P300 (P3) component of the event-related potential was assessed in three experiments. In each study an auditory discrimination paradigm was employed wherein subjects indicated with a finger tap response the occurrence of a randomly presented 2000 Hz target tone embedded in a series of 1,000 Hz tones. Target stimuli were presented with a probability of either .20 or .80 in different conditions which were combined factorially with different interstimulus intervals. Experiment 1 presented stimuli at 2.0, 2.5, or 3.0 second intervals; Experiment 2 presented stimuli at 2.0, 3.0, or 4.0 second intervals; Experiment 3 presented stimuli at 4.0, 6.0, or 10.0 second intervals. P3 amplitude was larger for the .20 relative to the .80 target probability conditions for the shorter interstimulus intervals but not for the longer intervals. P3 latency was consistently longer for the .20 relative to the .80 target probability conditions, with generally little effect observed for interstimulus interval changes. The results suggest that interstimulus interval affects component amplitude by determining the amount of processing resources available when the P3 is produced.     

Inhibition of the eyeblink reflex in the human infant

In human adults the eyeblink elicited by a given stimulus can be inhibited if that stimulus is preceded by another stimulus at an appropriate lead interval. In the present work, pairs of eyeblink-eliciting stimuli separated by 300-1200 msec were presented to sleeping preterm and full-term infants as well as to adults. Preterm infants did not exhibit reliable inhibition at any interval. Full-term infants did so, but they required longer interstimulus intervals than were needed for inhibition in the adult subjects. Results imply that the neural systems that mediate reflex inhibition are functional at birth, but that they are relatively slow to act.     

Nonlinear systems analysis of the hippocampal perforant path-dentate projection. III. Comparison of random train and paired impulse stimulation

1. The transformational properties of the network of hippocampal neurons activated monosynaptically and polysynaptically by electrical stimulation of the perforant path were analyzed using random impulse train and paired impulse stimuli. In response to both types of input, the amplitudes of granule cell population spikes evoked in the dentate gyrus were used as the measure of network output. The random stimulus train consisted of a series of 4,064 electrical impulses, with interimpulse intervals determined by a Poisson distribution; the mean interimpulse interval of the train was 500 ms, and the range was 1-5,000 ms. Paired impulse stimuli consisted of pairs of impulses separated by 10-1,200 ms; impulses pairs were delivered once every 20 s. The procedures were applied to both anesthetized and chronically implanted, unanesthetized preparations. 2. Nonlinear systems analysis of population spike responses evoked during random train stimulation revealed that dentate granule cell output to any impulse was highly dependent on the interval since a prior impulse. Data from anesthetized animals showed that population spike amplitudes were markedly suppressed in response to intervals less than 50 ms, facilitated in response to intervals of approximately 100 ms, suppressed slightly in response to intervals of 300-700 ms, and unaffected by intervals greater than 700 ms. Data from unanesthetized animals showed similar results except that facilitation rather than suppression of spike amplitude was observed in response to intervals of 300-700 ms, and could extend to intervals as great as 1,000 ms. 3. The results of paired impulse stimulation applied to the same preparations also showed that granule cell response was highly dependent on interimpulse interval. However, nonlinearities observed with paired impulse stimulation differed from those revealed by a random impulse signal. Compared to results of random train stimulation, a paired impulse format produced greater magnitude spike suppression in response to short interimpulse intervals (e.g., 10-20 ms), maximum facilitation in response to shorter interstimulus intervals (50 ms rather than 100 ms), greater magnitude spike facilitation, and greater suppression in response to intervals greater than or equal to 300 ms. Furthermore, there were virtually no differences in the nonlinearities of granule cell response recorded from anesthetized and unanesthetized animals when a paired impulse format was used, whereas several differences were observed with random train stimuli. 4.(ABSTRACT TRUNCATED AT 400 WORDS)     

Stimulus Intensity and Recency Contrasts and Orienting Response Strength

Several groups of 30 college students heard sequences of noise pulses. Skin conductance response (SCR) magnitudes revealed that intensity and recency effects remain effective during habituation trials. Habituation of the SCR magnitude occurred to stimuli that were presented in a pattern composed of two intensities and to stimuli in a pattern of two interstimulus intervals though the specific differential effects of level of intensity and of recency remained clearly evident. There appeared further an enhancement of response magnitude to intense stimuli (an apparent contrast effect) when they were presented in that pattern of two intensities and compared to response to suitable control sequences. After significant but not complete habituation occurred, a reduction in stimulus intensity or of interstimulus interval reduced SCR magnitude further. The findings were discussed as supplements to Sokolov's habituation theory.     

Concomitant Heart Rate and Eyeblink Pavlovian Conditioning in Human Subjects as a Function of Interstimulus Interval

Pavlovian heart rate and eyeblink conditioning were simultaneously assessed in human subjects. Tone durations of 0.6, 1.1, and 2.1 s were employed in separate groups of subjects as the conditioned stimulus. A 100-ms corneal airpuff, which served as the unconditioned stimulus, overlapped the last 100 ms of the tone in each group, thus producing interstimulus intervals of 0.5, 1.0, and 2.0 s. Other groups of pseudoconditioning subjects received explicitly unpaired tone and airpuff presentations of identical durations but in a pseudorandom sequence so that they never occurred together. The best eyeblink conditioning was observed in the group with the .5-s interstimulus interval, although the 1.0-s group also demonstrated some evidence of eyeblink conditioning. The group with the 2.0-s interstimulus interval showed a lower overall rate of conditioned response occurrence and the highest rate of pseudoconditioned responding. The conditioned heart rate response in all three conditioning groups consisted of cardiac decelerations, but tone-evoked cardiac accelerations were observed in the pseudoconditioning groups. The magnitude of the cardiac deceleration was comparable in all three conditioning groups.     

Sensory interaction: Evoked potential observations in man

Summary Polysensory averaged evoked potentials were evaluated as a function of the interval between a flash and a click which followed it at intervals ranging from 20—120 msec. This was done in two experimental series in each of which the subject's task was to respond manually to the flash. One of these required a choice reaction, namely, withholding of motor response when click was occasionally presented alone.Both evoked potential amplitude and reaction times showed a linear relationship to interstimulus interval; at shorter intervals, the amplitude of the polysensory evoked response was higher and reaction times were faster.Topographical analysis indicated that the electrophysiological findings were more consistently obtained in recordings from transverse bipolar leads than from pairs in the anterior-posterior plane. Responses recorded from the left motor region (contralateral to the arm employed in the manual response) showed the effect more consistently than did those from the homotopic recording site on the right motor cortex.Ratios were calculated between the amplitude of the obtained polysensory evoked responses and a theoretical one expected by algebraic addition of the responses to the two stimuli as presented singly. It was found that ratios were consistently higher for the left motor region when compared to the right. Only at the left was there a reliable relationship between interstimulus interval and the calculated ratio, with values greater than one at short interstimulus intervals and a linear decrement in the ratio value as interstimulus interval lengthened.Supported by NASA grant NsG 215-62     

Stimulus duration and repetition rate influence newborns' head orientation toward sound

Three experiments evaluated the effects of stimulus duration and repetition rate on newborns' head orientation responses. In Experiment 1, 28 infants turned toward a 20-sec continuous rattle sound but not toward 14- and 500-msec rattle sounds. Signal energy as a possible explanation for the infants' difficulty orienting toward brief sounds was explored in Experiment 2. Twenty neonates did not turn toward a single 90 dB, 14-msec rattle sound, although a longer duration (10 sec) sound containing less energy (70 dB) did elicit reliable head orientation. In Experiment 3, 16 neonates heard trains of repeated 14-msec rattle sounds (2/sec, 1.3/sec, and 1/sec) lasting 10 sec as well as a 10-sec continuous rattle sound. They turned toward the most rapidly repeating brief sound and the continuous one, while the slowly repeating sounds elicited little head movement in any direction. These results suggest that newborns' head orientation is selectively deficient for brief sounds, that the difficulty does not result from lessened energy in the brief sounds, and that the efficacy of repeated brief sounds depends upon their repetition rates.     

Functionally distinct subpopulations of striatal neurons are differentially regulated by GABAergic and dopaminergic inputs--II. In vitro analysis.

In the companion report [Nisenbaum and Berger (1992) Neuroscience 48, 561-578] the contrasting paired impulse responses to stimulation of the corticostriatal pathway which define the Type I and Type II subpopulations of striatal neurons were shown to reflect differential regulation by GABAergic and dopaminergic inputs. More specifically, the decreased probability of spike discharge (inhibition) to long interstimulus intervals (60-260 ms) characteristic of Type I neurons was found to be dependent on dopaminergic input via D1 receptor activation, whereas the inhibition to short interstimulus intervals (10-20 ms) distinctive of Type II neurons was found to be mediated by GABAergic input acting through GABAA receptor stimulation. The present experiments have further investigated the contribution of GABAergic and dopaminergic feedforward and/or feedback circuits to the functional identities of Type I and Type II neurons using an in vitro corticostriatal slice preparation. In this preparation, the cortical afferents to the striatum are preserved, allowing for activation of striatal cells in a manner similar to that used in vivo; however, all axons arising from midbrain and brainstem structures including the substantia nigra are transected, and intrastriatal GABAergic pathways are reduced. Consistent with the predicted effect of disrupting these two neurotransmitter pathways, the paired impulse responses of striatal neurons recorded in vitro were not similar to the responses of either Type I or Type II neurons recorded in vivo. Indeed, the paired impulse profiles of striatal neurons recorded in vitro were relatively homogeneous in that virtually all cells displayed an increased probability of spike discharge (facilitation) to the second impulse of all interstimulus intervals (10-500ms) tested. Low concentrations of allosteric agonists for the GABAA receptor, pregnanolone (5 microM) and pentobarbital (50 microM), selectively inhibited spike discharge in response to short interstimulus intervals (10-20 ms) for approximately 40% of the neurons sampled, but produced no change in facilitation to longer interstimulus intervals (30-500 ms). The agonist-induced inhibition to short interstimulus intervals was blocked by bicuculline (10-20 microM), and was not mimicked by the GABAB receptor agonist, baclofen (1-5 microM). In addition, application of dopamine (5-10 microM) or the D1 receptor agonist, SKF38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; 5 microM), inhibited spike discharge to longer interstimulus intervals (40-500 ms) for approximately 10% of striatal cells recorded. The inhibition to longer interstimulus intervals was blocked by the D1 receptor antagonist, SCH23390 [R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin+ ++-7-ol], but not the D2 antagonist, sulpiride.(ABSTRACT TRUNCATED AT 400 WORDS)     

The Q-oTc and Q-Tc interval and ionized calcium in newborns

Ionized calcium (CaF), Q-oTc and Q-Tc intervals were determined in 31 full-term healthy newborns, 12 infants subjected to blood exchange transfusion (ET) and 10 infants with verified clinical hypocalcaemia. There was no significant correlation between CaF values and QT intervals. The large fluctuations in CaF during ET did not correspond to any similar change in Q-oTc or Q-Tc intervals. The Q-oTc interval was slightly longer in the hypocalcaemic and the blood exchanged groups compared to controls. The Q-Tc interval was somewhat longer in the ET group. The differences in mean values for QT intervals were fairly small and the ranges wide. ECG findings lack practical implications in diagnosing and following neonatal hypocalcaemia and we therefore recommend the measurement of CaF as a guideline.     

Directing Attention Toward Stimuli Affects the P300 But Not the Orienting Response

Whether attending to stimuli affects the orienting response and its habituation is not yet clear. EEG alpha suppression responses, electrodermal responses, and EEG evoked potential responses of two groups of subjects were compared. The Attend group was given instructions to pay attention to and count the 59 moderate intensity clicks (interstimulus interval = 15 sec). The Ignore group was instructed to “try not to let the clicks disturb your relaxed state.” Separate ANOVAs with repeated measures were used to evaluate all measures, and all showed significant effects for click repetition (habituation). Alpha suppression and change in log conductance showed no differences related to group. The P300 component of the average evoked potentials was significantly larger for the Attend group. We concluded that attending to, versus ignoring, stimuli does not have an appreciable effect on these two traditional measures of the orienting response, but it does affect the evoked potentials. The relationship between attention and “significance” is discussed.     

Mismatch Negativity in Event-Related Potentials to Auditory Stimuli as a Function of Varying Interstimulus Interval

The mismatch negativity, isolated as a component of the event-related brain potential elicited by deviant auditory stimuli, was suggested by Näätänen (1984) as an indirect measure of the inferred neuronal representation of standard stimuli. The purpose of the present study was to determine the duration of the neuronal representation by varying the interstimulus intervals of 1, 6, and 10 seconds within experimental blocks. Mismatch negativities were found to be elicited by deviant stimuli (1500-Hz tones, sequential probability 10%) following standard stimuli (1000-Hz tones) with interstimulus intervals of 1, 6, and 10 s as well. The results suggest a duration of neuronal representation of at least 10 s. The within-block variation of interstimulus interval, the rather low temporal probability of deviants, and their large frequency deviance might explain the present results contradicting earlier findings that suggested a shorter duration of that neuronal representation.     

The GABA(B) receptor antagonist CGP 55845A reduces presynaptic GABA(B) actions in neocortical neurons of the rat in vitro.

Use-dependent depression of inhibitory postsynaptic potentials was investigated with intracellular recordings and the paired-pulse paradigm in rat neocortical neurons in vitro. Pairs of stimuli invariably reduced the second inhibitory postsynaptic potential-A (GABA(A) receptor-mediated inhibitory postsynaptic potential) of a pair; at interstimulus intervals of 500 ms, the amplitude of the second inhibitory postsynaptic potential-A was considerably smaller than the first (36.2 +/- 6.2%, n= 17). Decreasing the interstimulus interval reduced the second inhibitory postsynaptic potential-A further and with interstimulus intervals shorter than 330 ms the compound excitatory postsynaptic potential-inhibitory postsynaptic potential response reversed from a hyperpolarizing to a depolarizing response. The depression of the inhibitory postsynaptic potential-A exhibited a maximum at interstimulus intervals near 150 ms and recovered with a time constant of 282 +/- 96.2 ms. Elimination of excitatory transmission by the application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D(-)-2-amino-5-phosphonovaleric acid yielded an essentially unaltered time-course of paired-pulse depression (maximum depression near 150 ms, time constant of recovery 232 +/- 98 ms). The polarity change of the compound excitatory postsynaptic potential response at shorter interstimulus intervals was abolished in the presence of CNQX and D(- )-2-amino-5-phosphonovaleric acid. CNQX and D(-)-2-amino-5-phosphonovaleric acid also reduced the apparent depolarizing shift of the reversal potential between the first and second inhibitory postsynaptic potential-A from about 6 mV to less than 2 mV. Application of the GABA(B) receptor antagonist CGP 55845A in the presence of CNQX and (-)-2-amino-5-phosphonovaleric acid abolished the inhibitory postsynaptic potential-B and paired-pulse depression. Under these conditions, the amplitude of the second inhibitory postsynaptic potential was, on average, about 90% of the first, i.e. reduced by about 10%. The second inhibitory postsynaptic potential-A was approximately constant at interstimulus intervals between 100 and 500 ms. It is concluded that paired-pulse depression of cortical inhibition is predominantly mediated by presynaptic GABA(B) receptors of GABAergic interneurons. The abolition of net inhibition at interstimulus intervals near 330 ms may facilitate spread of excitation and neuronal synchrony during repetitive cortical activation near 3 Hz. This use-dependent depression of inhibition may contribute to highly synchronized slow electroencephalogram activity during spike-and-wave or delta activity.     

Nonlinear systems analysis of the hippocampal perforant path-dentate projection. II. Effects of random impulse train stimulation

1. Nonlinear systems analytic techniques were used to characterize transformational properties of the network of neurons activated by perforant path input to the rabbit hippocampus. Trains of 4,064 impulses with randomly varying interimpulse intervals were used to stimulate perforant path fibers, and amplitudes of evoked dentate granule cell population spikes were measured. Interimpulse intervals of the random stimulus train were determined by a Poisson distribution with a mean interimpulse interval of 500 ms, and with intervals ranging from 1 to 5,000 ms. The response of dentate granule cells to this stimulation was assumed to reflect activity in the larger hippocampal network, because other subpopulations of neurons activated monosynaptically and polysynaptically within the hippocampal formation contribute to granule cell excitability through multiple feedforward and feedback pathways. System properties were characterized both for halothane anesthetized and chronically implanted, unanesthetized preparations. 2. Second-order kernel analysis showed that population spike amplitude was highly dependent on interimpulse interval. When population spikes of all latencies were included in the same analysis, stimulation impulses produced near-total suppression of spike amplitude when they were preceded 10-20 ms by another impulse in the train. Spike suppression extended to approximately 50 ms and was inversely related to length of the interimpulse interval. Suppression of granule cell response to intervals within the range of 10-50 ms was not influenced by halothane anesthesia. 3. Interstimulus intervals greater than approximately 50 ms resulted in a facilitation of population spike amplitude, with maximum facilitation occurring in response to intervals of 90-100 ms. The magnitude of maximum facilitation was significantly greater for anesthetized (129%) than for unanesthetized (74%) preparations. The range of intervals resulting in facilitation for unanesthetized animals could extend to 1,000-1,100 ms (average range, 61-714 ms). This was much greater than observed for population spikes recorded from anesthetized animals (50-364 ms), which exhibited suppression in response to intervals of approximately 300-700 ms. 4. Further analysis revealed that the nature of nonlinearities in population spike amplitude may depend on spike latency. For example, population spikes of "short" latency (3-4 or 4-5 ms, depending on the animal) exhibited only facilitation in response to interstimulus intervals of 1-4 ms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Attentional modulation of blink startle at long, short, and very short lead intervals

The present research investigated attentional blink startle modulation at lead intervals of 60, 240 and 3500 ms. Letters printed in Gothic or standard fonts, which differed in rated interest, but not valence, served as lead stimuli. Experiment 1 established that identifying letters as vowels/consonants took longer than reading the letters and that performance in both tasks was slower if letters were printed in Gothic font. In Experiment 2, acoustic blink eliciting stimuli were presented 60, 240 and 3500 ms after onset of the letters in Gothic and in standard font and during intertrial intervals. Half the participants (Group Task) were asked to identify the letters as vowels/consonants whereas the others (Group No-Task) did not perform a task. Relative to control responses, blinks during letters were facilitated at 60 and 3500 ms lead intervals and inhibited at the 240 ms lead interval for both conditions in Group Task. Differences in blink modulation across lead intervals were found in Group No-Task only during Gothic letters with blinks at the 3500 ms lead interval facilitated relative to control blinks. The present results confirm previous findings indicating that attentional processes can modulate startle at very short lead intervals.     

Probing the orienting response with startle modification and secondary reaction time

Current models of orienting suggest a relationship between the orienting response and attentional processing. This relationship was examined using two independent probe techniques to index attentional processing: secondary reaction time and startle eyeblink modification. Twenty-eight college-age subjects received intermixed presentations of to-be-attended and to-be-ignored tones. Skin conductance orienting responses were obtained during a subset of the tones. Each of the remaining tones contained either a secondary reaction time probe at lead intervals of 150 or 2,000 ms or a startle eyeblink probe presented at lead intervals of 120 or 2,000 ms. In addition, reaction time and startle probes also were presented during selected intertone intervals, and responses to these stimuli served as the baselines from which to compare changes in reaction time and blink amplitude produced by the attended and ignored tones. The results revealed that, compared with the ignored tones, the attended tones were associated with larger skin conductance orienting responses, greater blink inhibition at the 120-ms lead interval, greater blink facilitation at the 2,000-ms lead interval, and greater reaction time slowing at the 2,000-ms lead interval. Consistent with previous findings, the ignored tone was associated with greater reaction time slowing than was the attended tone at the 150-ms lead interval. The results support a relationship between elicitation of the skin conductance orienting response and attentional processes and suggest that the secondary reaction time and blink modification techniques may provide unique information regarding this relationship.     

Maturational changes in heart rate and heart rate variability in low birth weight infants

To provide insight into the maturation of neural mechanisms responsible for variability in heart rate during quiet and active sleep, 6-hour continuous electrocardiographic recordings and simultaneous minute-by-minute behavioral activity state assignments were performed in 61 healthy, growing low birth weight infants. The infants weighed 795-1600 g at birth and ranged between 31-38 weeks in postconceptional age. During this age interval there was a decrease in heart rate during quiet sleep and an increase in both time domain and frequency domain measures of the variability in cardiac interbeat intervals. In quiet sleep, global variability, measured as SD of R-R intervals, increased in relation to age, as did higher frequency variability, measured as the square root of the mean of squared successive differences in R-R intervals. Developmental changes in the 0.5-2.0 Hz spectral power band of RR-interval variability, another measure of high frequency variability, paralleled the changes seen in the time domain measure. Evaluation of patterns of changes in the magnitude and direction of successive interbeat intervals provided evidence that the incidence of sustained accelerations or decelerations increased whereas the incidence of no change in consecutive RR-intervals decreased as infants matured. Among the various measures of heart rate variability, the incidence of sustained change and no change in successive interbeat intervals were most closely related to postconceptional age in both sleep states. The overall decrease in heart rate, increase in heart rate variability, and increase in the pattern of changes in interbeat interval with postconceptional age are consistent with the maturation of the autonomic cardio-regulatory activity from 31-38 weeks age.     

Blood Pressure and Heart Rate Changes Accompanying Classical Eyeblink Conditioning In The Rabbit (Oryctolagus Cuniculus)

In two experiments employing 38 rabbits differential classical conditioning of heart rate, blood pressure, and corneoretinal potential (CRP) response were examined using l-sec and 4-sec interstimulus intervals ISI respectively. The conditioned response consisted of HK decelerations and DP depressor responses early in conditioning. However, many, but not all, animals revealed pressor responses and HR accelerations after the CRP discrimination was acquired. Significant correlations were also obtained between BP pressor responses, HR accelerations, and the frequency of CRP CRs. These results were discussed within the context of the orienting and defense reflexes.