EEG characteristics prior to and following the evoked K-Complex.

Examined if the K-Complex reflects an arousal from sleep or a sleep protection mechanism. Ten 18–34-yr-old participants were presented auditory stimuli every 20 sec while asleep. Trials were sorted according to the presence or absence of a K-Complex. A fast Fourier Transformation of the data was computed on EEG segments prior to and following stimulus onset. The log power of activity in delta, theta, alpha, sigma, and beta bandwidths was computed. Results indicate that when a K-Complex was elicited, there were no differences in EEG activity prior to and following the stimulus. However, during slow wave sleep, when a K-Complex was not elicited, there was a significant overall increase in theta, alpha, sigma, and beta activity following stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

EEG asymmetry and heart rate during experience of hypnotic analgesia in high and low hypnotizables

This study evaluates the effects of hypnotic analgesia and hypnosis on bilateral EEG activity recorded from frontal, central and posterior areas during three painful electrical stimulation conditions: waking, hypnosis/no-analgesia, hypnosis/analgesia. Eight high-hypnotizable and eight low-hypnotizable (right handed) subjects participated in the experiment. The following measures were obtained: pain and distress tolerance ratings; EEG spectral amplitudes for the frequency bands: delta (0.5-3.75 Hz), theta 1 (4-5.75 Hz), theta 2 (6-7.75 Hz), alpha 1 (8-9.75 Hz), alpha 2 (10-12.75 Hz), beta 1 (13-15.75 Hz), beta 2 (16-31.75 Hz), total band (0.5-31.75 Hz), '40-Hz' (36-44 Hz); cardiac interbeat interval (ms); mid-frequency and high-frequency peaks from power spectral analysis of heart period variability. During hypnosis/analgesia, high hypnotizable subjects displayed significant reductions in pain and distress scores compared to hypnosis/no-analgesia and waking conditions. In each experimental condition these subjects displayed significant lower total and beta 1 amplitudes compared to low hypnotizables. High hypnotizables, on central and posterior recording sites, during both hypnosis/analgesia and hypnosis/no-analgesia conditions also showed total and delta EEG amplitude reductions in both hemispheres and a theta 1 amplitude reduction in the left hemisphere. However, for total, delta and beta 1 bands in the hypnosis/analgesia condition the amplitude reduction was more pronounced in the right hemisphere as shown by hemispheric asymmetry in favor of the left hemisphere. Low hypnotizables, on posterior recording sites, displayed a delta amplitude reduction during hypnosis/no-analgesia and hypnosis/analgesia conditions. These subjects also showed, for all recording sites, a reduction in theta 1 amplitude during hypnosis/no-analgesia compared to the waking condition. Lows, however, failed in evidencing amplitude differences between hypnosis/no-analgesia and hypnosis/analgesia conditions. During hypnotic analgesia the hemispheric asymmetry found in high hypnotizables was parallel to a significant reduction in the spectral mid-frequency peak of heart period variability which indicated a decrease in the level of sympathetic activity. In contrast, during hypnosis/no-analgesia the EEG amplitude reduction was not paralleled by a decrease in sympathetic activity.     

A possible role of evoked alpha in primary sensory processing: common properties of cat intracranial recordings and human EEG and MEG

Regarding the evoked potential (EP) as a superposition of evoked EEG rhythms in several frequency ranges, we investigated the following issue: Are distinct evoked rhythms, in particular the alpha (8-15 Hz) response, related to separable physiological processes? Frequency domain analysis of EPs was used to evaluate results of cross-modality experiments, i.e.: responses to auditory stimuli were simultaneously recorded from the auditory cortex (adequate stimulation) and from the visual cortex (inadequate stimulation). Responses to visual stimuli were recorded from the same sites. The results of these experiments and further measurements (EEG and MEG responses in humans, among them multiple sclerosis patients) are consistent in the following respect: The amplitudes of alpha responses are dependent on whether or not a stimulus applied is adequate. Alpha responses may thus be related mostly to primary sensory processing. In contrast, theta responses (4-7 Hz) were observed for adequate as well as inadequate stimuli. They may be related rather to associative and cognitive processing than to primary sensory processing. Thus frequency responses, in particular the alpha response, are not artificial results of digital filtering, but functionally significant brain responses.     

Spectral analysis in cyclic changes of human sleep evaluation

In this study cyclic changes of human sleep structure were examined. For whole-night polysomnograms of 35 healthy volunteers of both sexes, manual hypnograms were created and divided into NREM-REM cycles. EEG signals from C3-A2 derivation were analysed by computer using a Fast Fourier Transform (FFT). For consecutive NREM-REM cycles of individual sleep stages, EEG power density contents for delta, theta, alpha, sigma and beta waves were analysed. For consecutive sleep cycles, a clear decrease in NREM sleep duration, especially slow wave sleep duration, was obtained. In addition, a decrease in power density of delta waves was observed. For consecutive sleep cycles, increases in REM sleep duration and in power density of theta and alpha waves were obtained. In consecutive sleep cycles, high amplitude delta slow waves are replaced by higher frequency and lower amplitude waves. Thus stages of NREM sleep are replaced by stages of REM.     

Integration of health care economics for addiction treatment in clinic care

Visceral pain is a substantial, clinical problem but unfortunately few experimental models are available to study this phenomenon in man. In the present study we inserted a stimulation catheter 5-10 cm into the ileo-sigmoidostomy of nine patients. The catheter contained six small, flexible electrodes separated by 4 mm. The gut was stimulated by single burst, repeated burst (five stimuli delivered at 2 Hz), or continuous burst stimuli (4 Hz for 30, 60, 90, and 120 s). The sensation (ST), pain detection (PDT), and pain tolerance (PTT) thresholds to single/repeated burst stimuli were determined. The location/size/sensitivity of referred pain after repeated/continuous stimulation were characterized. The brain potentials to single burst stimuli and to increasing stimulus intensity were measured. ST to single burst stimuli was easy to determine (8 mA) and to reproduce. The patients found it difficult to determine the PDT and PTT to single burst stimuli, however both thresholds were easily determined for repeated burst stimuli. The pain thresholds to single burst stimuli were twice as high as the thresholds to repeated burst stimuli, indicating the importance of central temporal summation for visceral pain. Minor changes in the stimulus location resulted in changes of the referred pain projection site. The words most frequently selected (78%) from the McGill Pain Questionnaire to describe repeated burst stimulations were shooting, pricking, flashing, and boring. The amplitude of the brain potentials increased at increasing stimulus intensity. A stimulus intensity giving an initial pain rating of around 5 on a 0-10 visual analog scale (VAS) was used for continuous stimulation. A general increase of the pain intensity and the area of referred pain was found during this stimulation. It was concluded that electrical stimulation of the human gut provokes pain and especially long sequences of visceral stimuli are adequate to evoke referred pain mimicking pain profiles of pathologic origin.     

Coherence analysis of the human sleep electroencephalogram

Animal studies have shown that the sleep-related oscillations in the frequency range of spindles and slow-waves, and in the gamma band occur synchronously over large parts of the cerebral cortex. Coherence analysis was used to investigate these oscillations in the human sleep electroencephalogram. In all-night electroencephalogram recordings from eight young subjects power and coherence spectra within and between cerebral hemispheres were computed from bipolar derivations placed bilaterally along the antero-posterior axis. The 0.75-50 Hz range was examined with a resolution of 0.25 Hz. Distinct peaks in coherence were present in non-rapid eye movement sleep but not in rapid eye movement sleep. The most prominent and consistent peak was seen in the range of sleep spindles (13-14 Hz), and additional peaks were present in the alpha band (9-10 Hz) and low delta band (1-2 Hz). Whereas coherence in the spindle range was highest in stage 2, the alpha peak was most prominent in slow-wave sleep (stages 3 and 4). Interhemispheric coherence at 30 Hz was higher in rapid eye movement sleep than in non-rapid eye movement sleep. There were also marked sleep state-independent regional differences. Coherence between homologous interhemispheric derivations was high in the low frequency range and declined with increasing frequencies, whereas coherence of intrahemispheric and non-homologous interhemispheric derivations was at a low level throughout the spectra. It is concluded that coherence analysis may provide insights into large-scale functional connectivities of brain regions during sleep. The high coherence of sleep spindles is an indication for their widespread and quasi-synchronous occurrence throughout the cortex and may point to their specific role in the sleep process.     

Prestimulus EEG-activity strongly influences the auditory evoked vertex response: a new method for selective averaging

A new algorithm for averaging of evoked potentials (EPs) is introduced and compared with the conventional method. The root mean square (rms) values of the alpha and theta band EEG activities 1-s preceding stimulus presentation were computed: stimuli were blocked during phases of high prestimulus activity, thus evoking auditory responses selectively during periods of low activity. Ten volunteers were stimulated with tone bursts of 2000 Hz, 80 dB and 1-s duration. The main results were: (1) The averaged EPs showed an increase in amplitude of nearly 40% in comparison to experiments with conventional stimulation. This increase was in the range of 30% when an ISI correction was taken into account. (2) Single trials tended to form patterns of damped oscillations of e.g., 7-8 Hz, thus revealing a high correlation to the averaged EP. In alpha or theta band contingent experiments, correlation coefficients between single trials and averaged EPs were significantly higher (p < .01; p < .05).     

Relationship of cerebral oxygen uptake to EEG frequency in isolated canine brain

Cerebral oxygen uptake was correlated with electroencephalographic (EEG) frequency and amplitude in 87 isolated canine brains. Group I (71 brains) was perfused with diluted blood and Group II (16 brains) was perfused with whole blood equilibrated with oxygen at various partial pressures. The EEG's were classified as follows: A, highest frequency greater than or equal to 17 Hz, alpha (8-13 Hz) amplitude less than 50 muv, delta (less than or equal to 3.5 Hz), amplitude less than 100 muv; B, highest frequency greater than or equal to 17 Hz, alpha amplitude greater to or equal to 50 muv, and/or delta amplitude greater than or equal to 100 muv. C, highest frequency 8-16 Hz, alpha amplitude greater than or equal to 25 muv, and delta amplitude greater than 100 muv, D, highest frequency 0.5-16 Hz, alpha, if present, amplitude less than 25 muv, and/or delta amplitude less than 100 muv, and E, highest frequency 0-16 Hz, alpha, if present, amplitude less than 10 muv, and/or delta amplitude less than 15 muv. The Group I oxygen uptakes in ml/100 g of brain per min+/-SE for the five EEG classifications were A, 4.39+/-0.06, B, 4.13+/-0.08, C, 3.76+/-0.09, D, 3.40+/-0.12, and E, 2.55+/-0.06, whereas the corresponding Group II values were A, 4.64+/-0.22, B, 4.28+/-0.15, C, 3.82+/-0.24, D, 3.39+/-0.40, and E, 1.38+/-0.42. As the EEG deteriorates, cerebral oxygen uptake tends to decrease in a significant and parallel manner in both the diluted and whole blood groups.     

The rotatory machines in the history of psychiatry

In this study, we recorded the event-related potentials (ERPs) elicited by stimuli appearing at attended and unattended locations. The voltage amplitudes and latencies of the P1, N1, P2, N2 and P3 visual components showed statistically significant differences in the attended condition with respect to the unattended one. The power spectral density of the EEG following stimulus onset was calculated. The difference between the spectral densities of the attended and unattended conditions was computed. Statistically significant differences were found in the decrease of alpha (9-11 Hz) and the increase of beta (15-17 Hz) frequencies during the attention condition with respect to the unattended condition. These results suggest that the arrival of a visual stimulus during the attended condition generates a complex reorganization of neuronal activity in both time and frequency domains.     

Fear conditioning increases NREM sleep.

To understand the role that sleep may play in memory storage, the authors investigated how fear conditioning affects sleep-wake states by performing electroencephalographic (EEG) and electromyographic recordings of C57BL/6J mice receiving fear conditioning, exposure to conditioning stimuli, or immediate shock treatment. This experimental design allowed us to examine the effects of associative learning, presentation of the conditioning stimuli, and presentation of the unconditioned stimuli on sleep-wake states. During the 24 hr after training, fear-conditioned mice had approximately 1 hr more of nonrapid-eye-movement (NREM) sleep and less wakefulness than mice receiving exposure to conditioning stimuli or immediate shock treatment. Mice receiving conditioning stimuli had more delta power during NREM sleep, whereas mice receiving fear conditioning had less theta power during rapid-eye-movement sleep. These results demonstrate that a single trial of fear conditioning alters sleep-wake states and EEG oscillations over a 24-hr period, supporting the idea that sleep is modified by experience and that such changes in sleep-wake states and EEG oscillations may play a role in memory consolidation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Induction of COX-2 expression by mechanical tension force in human periodontal ligament cells

Spectral EEG powers were compared in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) in a group of 20 subjects during the performance of tasks requiring mental rotation of two- and three-dimensional objects. Only those EEG segments corresponding to tasks with identical solution times were analyzed. The spectral powers of oscillations in the alpha range were higher in control conditions than during task performance. Power in the frequency range 15-45 Hz was greater during task performance than in control conditions; this supports the concept that alpha rhythm desynchronization accompanies the synchronization of higher-frequency EEG rhythms. Frequency power during task performance with two-dimensional objects was greater than that during tasks with three-dimensional objects. Since the angle of rotation between two-dimensional objects was greater than that between three-dimensional objects, this factor, rather than the depth of the perceived space, increased the level of cortical activation. In all experimental situations, power at frequencies of 15-45 Hz was significantly greater in the occipital regions than any other regions, reflecting the visual modality of the stimulus. Particular changes were noted in the gamma range (35-45 Hz), where power in the first second of task performance was significantly higher than in the second second; this may provide evidence that this range is more closely associated with perception and recognition processes than with mental transformation of the image.     

Mesograde amnesia during the sleep onset transition: replication and electrophysiological correlates

The present study was designed to explore mechanisms of amnesia for meaningful auditory material presented during the sleep onset transition. Thirty undergraduate subjects (17 female, 13 male) were presented with auditory stimuli in an oddball paradigm until sleep onset. Subjects were allowed to accumulate either 30 seconds or 10 minutes of sleep, then awakened and tested on free recall and recognition memory for the meaningful stimuli. After 10 minutes of sleep, but not after 30 seconds of sleep, subjects had profound amnesia on free recall for stimuli presented in the 4-minute window prior to sleep onset. Increased beta electroencephalograph (EEG) power during the sleep period correlated positively with recall of stimuli in the 4-minute presleep window. Event-related potential recordings provided suggestive evidence that subjects continued to process the auditory stimuli to some extent during the sleep onset transition. When allowed to sleep for 10 minutes, subjects evidenced a mixed anterograde and retrograde amnesia for auditory stimuli presented in the 4-minute window prior to sleep onset. The results are discussed in terms of stimulus encoding, consolidation, and retrieval.     

Antisense WT1 transcription parallels sense mRNA and protein expression in fetal kidney and can elevate protein levels in vitro

The intensity of a pain-only decompression sickness (DCS) symptom with respect to time at altitude increases, peaks, and then declines in some cases. A similar pattern is also seen in a graph of the probability density function [f(t)] for DCS. The f(t) is the proportion of DCS per unit time with respect to time at altitude. The integration of f(t) with respect to time provides the cumulative probability of DCS [P(DCS)]. We suspect that the perceived intensity of pain with a given stimulus intensity is related to the P(DCS); it may be related to the intensity of the stimulus to a power (alpha). Our stimuli are defined as pressure ratio [PR = (phi P1N2/ P2)-11] or pressure difference [delta P = phi P1N2-P2], where phi P1N2 is the N2 partial pressure calculated in the 360 min half-time (t1/2) compartment or t1/2 is estimated with other parameters and P2 is ambient pressure after the ascent. Both stimuli represent a potential released volume of gas. We tested the null hypothesis that alpha > 1 was no better than alpha = 1 in PR alpha and delta P alpha in a log logistic survival analysis of 1085 exposures in hypobaric chambers. The log likelihood number increased from -1198 for alpha = 0 for the null model to -724 for PR alpha when alpha = 3.52 with a 42 min t1/2 and -714 for delta P alpha when alpha = 8.44 with a 91 min t1/2. We conclude that the improvement in our expressions for decompression dose with alpha > 1 is not by random chance and that alpha may link the physics of gas evolution to the biology of pain perception. Because of our empirical approach, we do not exclude other possible interpretations.     

A noncompliant patient with fluctuating capacity

Poor sleep, daytime fatigue, and loss of cognitive ability exist during all stages of HIV infection, worsening with disease progression. These symptoms contribute to disability and poor quality of life. Data from several research groups support a role of somnogenic inflammatory process peptides elevated in HIV infection, e.g. TNF alpha. Though the literature is in conflict regarding an effect of HIV infection on growth hormone (GH) secretion, GH axis dysregulation and treatment with GH may be important in HIV infection, e.g. in the wasting syndrome. It has long been known that GH varies with changes in sleep. The hypothesis tested in the current study was that the relationship between delta frequency (0.5-4.0 Hz) sleep EEG amplitude (square root of power from frequency analysis) and GH secretion would differ between HIV positive (HIV+) and HIV negative (HIV-) subjects. In 14 subjects (6 HIV+ and 8 HIV-, none with current or past AIDS-defining illness) a linear relationship change across the night's sleep was found in the coupling between delta frequency sleep EEG amplitude and GH secretion. The phase coupling change was in opposite directions in HIV+ versus HIV- subjects. This difference supports the hypothesis that the brain-based coordination of sleep and sleep-related physiology deteriorates early in HIV infection, and that GH dysregulation may contribute to this sleep pathology.     

Serum lipids and vitamin A, C and E concentrations in an adult population of Caracas City

OBJECTIVES: Event-related desynchronization (ERD) and synchronization (ERS) of the 8-10 and 10-12 Hz frequency bands of the background EEG were studied in 10 subjects performing an auditory lexical matching task. METHODS: The stimuli were words and pseudowords presented sequentially in pairs. The subject was prompted to answer whether the two stimuli shared the same lexical status (words or pseudowords). RESULTS: Regardless of lexicality, the presentation of the first stimulus elicited a significant late frontal ERD in both alpha frequency bands. When preceded by a pseudoword, the presentation of the second stimulus elicited a significant ERS at 200-400 ms and a significant, long-lasting and topographically-widespread ERD at 600-2200 ms in both frequency bands. When preceded by a word, the second stimulus did not elicit ERS in the initial time window, but a late ERD which was similar to the one observed in the previous condition. The complexity of ERD/ERS changes in the present task was revealed by significant interactions that time had with frequency band, stimulus type, stimulus order and lexicality of the preceding stimulus. CONCLUSIONS: The results suggest that ERD/ERS does not reflect primary auditory stimulus processing. Rather, the ERD/ERS observed in this experiment most probably reflected task difficulty and differences between lexical-semantic and phonological memory functions.     

Frontal Electroencephalogram Alpha Asymmetry During Sleep: Stability and Its Relation to Affective Style.

Electroencephalogram (EEG) alpha (8-12 Hz) asymmetries were collected from the mid-frontal and central regions during presleep wakefulness and Stage 1, Stage 2, and rapid eye movement (REM) sleep in 11 healthy right-handed participants who were free of psychiatric, neurological, and sleep problems. The authors found significant correlations between presleep wakefulness and different stages of sleep in the frontal, but not central, EEG alpha asymmetry measure. The strongest correlation was between presleep waking and REM sleep, replicating and extending relation earlier work to a normal population. The high degree of association between presleep waking and REM sleep may be a result of high cortical activation common to these states and may reflect a predisposition to different styles of emotional reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects on pubertal growth and reproduction in rats exposed to lead perinatally or continuously throughout development

The purpose of this study was to examine the effects of different exercise intensities with the anaerobic threshold (AT) as the standard on electroencephalograph (EEG) and heart rate variability (HRV). Eleven healthy males, with a mean age of 22 (SD 1.48) years, performed submaximal exercise to determine their ATs, and underwent four experimental conditions including rest (rest), 20% less than the AT level (-20), the AT level (AT), and 20% more than the AT level (+20) for about 20 minutes. EEG and electrocardiogram (ECG) were taken for 15 minutes before and after each experimental condition, respectively. The EEG signals were recorded from Cz, Pz, O1 and O2 (10-20 system). HRV was determined by the R-R interval method of ECG. Spectral analysis was applied to the EEG and the HRV from just before (pre) and after (post) each experimental condition for 5 minutes using the maximum entropy method (MEM). Post/pre ratios were calculated, after the power spectral density (PSD) and percentage of total power (power time percent: Time%) of delta (0.5-4 Hz), theta (4-8 Hz), alpha 1 (8-11 Hz), alpha 2 (11-14 Hz), beta 1 (14-20 Hz), beta 2 (20-30 Hz), total waves in EEG and PSD as to low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.4 Hz) areas, and the LF/HF(L/H) ratio in HRV were analyzed. In the exercise condition, total PSD in the EEG was enhanced and PSD of HF in HRV was significantly declined, as compared to those in the resting condition. Alpha PSDs of occipital sites were higher in -20 than those in AT and +20 conditions. The increase in L/H in AT and +20 demonstrated the changes in the balance of the autonomic nervous system, compared with that in -20. A significant increase in heart rate was observed in +20, although other indicators did not show differences in AT and +20 conditions. No alternations were noted in the gradient of exponential PSD in the above four experimental conditions, that is at rest, -20, AT and +20. These results suggest that the exercise intensity 20% less than one's AT level does not put a great strain on his or her body in health-promoting.     

Citalopram: differential sleep/wake and EEG power spectrum effects after single dose and chronic administration

The sleep/wake effects of the selective serotonin re-uptake inhibitor citalopram were studied in both a single-dose study with three dose levels (0.5, 2.0 and 5.0 mg/kg), and a 5-week chronic administration study (15 mg/kg/24 h). Single doses of citalopram resulted in a dose-dependent inhibition of rapid eye movement (REM) sleep. After chronic citalopram treatment there was a sustained REM sleep inhibition. Single doses of citalopram resulted in only minor changes in non-REM (NREM) sleep as well as in NREM EEG power spectral density. Chronic administration resulted in a major shift from SWS-2 to SWS-1. The observed corresponding changes in EEG power density were regional. A 30 to 40 percent reduction of power density in the 0.5-15 Hz range in the fronto-parietal EEG derivation was seen for the whole 8-h registration period. In the fronto-frontal EEG derivation only minor changes were seen. A decreasing trend in NREM sleep power density between 0.5 and 7 Hz, usually seen during the course of the light period, was not observed in the chronic condition, but was seen in control and single-dose condition, suggesting altered diurnal distribution of slow wave activity in the chronic condition. The data indicate that acute and chronic administration of citalopram shows clear differences in sleep effect, which may be caused by alteration of serotonergic transmission, and may be related to the antidepressant effect.     

Responses of cutaneous A-fiber nociceptors to noxious cold

Responses of cutaneous nociceptors to natural stimuli, particularly mechanical and heat stimuli, have been well documented. Although nociceptors are excited by noxious cold stimuli, there have been few studies of their stimulus-response functions for cold stimuli over a wide range of stimulus temperatures. Furthermore, the proportion of nociceptors excited by noxious cold is not clear. In the present study, we examined responses of mechanosensitive A delta-nociceptors and low-threshold mechanoreceptors to a wide range of cold stimuli that included stimulus temperatures <0 degrees C. Electrophysiological recordings were made from single primary afferent fibers in the saphenous nerves of anesthetized rats. Cutaneous sensory receptors were classed according to their conduction velocity and subgrouped functionally according to their responses evoked by mechanical, heat, and cold stimuli (0 degrees C). Responses evoked by a wide range of cold stimulus intensities that included stimuli considered innocuous and noxious (painful) were then assessed. Stimuli of 20 to -20 degrees C were delivered to the receptive field via a 1-cm2 contact thermode from a base temperature of 32 degrees C. Stimuli were applied in descending order of 2 degrees C decrements. Stimulus ramp rate was 5 degrees C/s, and stimulus temperatures were applied for a duration of 10 s. A total of 90 A fibers was studied, of which 61 were nociceptors and had conduction velocity in the A delta-range (2-30 m/s). Nociceptors were classed initially as mechanical, mechanoheat, and mechanocold nociceptors. The remaining 29 fibers were low-threshold mechanoreceptors with conduction velocity in the A delta- or A beta-range (>30 m/s). These were subgrouped according to their adaptive properties as slowly or rapidly adapting, and according to whether they were excited by hair movement (hair follicle afferent fibers). All nociceptors were excited by noxious cold. Only 30% of nociceptors were considered sensitive to cold on initial classification with the use of a cold stimulus of 0 degrees C. However, all nociceptors were excited by stimulus intensities <0 degreesC. Response thresholds for cold ranged from 14 to -18 degrees C (-4.6 +/- 1.07 degrees C, mean +/- SE). The total number of impulses, discharge rate, and peak discharge increased monotonically as intensity of cold stimuli increased. Power functions were used to determine the rate at which the number of impulses increased as stimulus intensity increased. The slopes of power funcions ranged from 0.12 to 2.28 (mean 1.07 +/- 0.13). Most mechanoreceptors were not excited by cold stimuli. The only types of mechanoreceptors that responded reliably to cold stimuli were the slowly adapting mechanoreceptors. Responses usually occurred during the temperature ramp when the skin temperature was decreasing. There was no evidence that mechanoreceptors encoded the intensity of cold stimuli at intensities above or below 0 degrees C, because evoked responses did not increase with intensity of cold stimuli. It is concluded that the proportion of cutaneous A delta-nociceptors excited by noxious cold stimuli has been underestimated in previous studies. All nociceptors were excited by stimulus temperatures <0 degrees C and encoded the intensity of cold stimuli. It is therefore likely that cutaneous A delta-nociceptors contribute to the sensation of cold pain, particularly pain produced by stimulus temperatures <0 degrees C.