Age related increased threshold for electroshock seizure in BDF1 mice

The thresholds for inducing the minimal and maximal electroshock seizures were examined in relation to age in BDF1 mice of both sexes. The 50 percent effective intensities for the maximal electroshock seizure (tonic hindlimb extensor component) were lowest in the youngest age groups (6-month-old) for both male (10.68 mA) and female (9.18 mA) animals. The threshold increased with age and became significantly higher at 24 months (14.00 mA, 12.70 mA for male and female mice respectively). There was also a further increase in threshold at 30 months for both sexes. Similarly, the threshold for inducing the minimal seizure also increased with age but the differences in mean threshold levels between the youngest and oldest groups were much smaller in comparison to the maximal seizure. It was concluded that the threshold for inducing electroshock seizures significantly increases with age in mice of both sexes.     

A study of caudate inhibition on an epileptic focus in the cat hippocampus

The mechanisms whereby the caudate nucleus modifies hippocampal spiking activity have been studied. Epileptiform activity was induced in the cat hippocampus by topical application of sodium penicillin in different concentrations. The frequency of induced spikes appeared to be directly correlated to the two doses of epileptogenic agent. The inhibitory effect of 10 Hz caudate stimulation on spike frequency was present even when stimulation lasted for 180 s. Likewise 25 Hz caudate stimulation brought about an inhibition which was maintained by stimulus trains lasting up to 90 s, while the degree of inhibition was reduced by trains of longer duration (120, 150 and 180 s); similar results were also noted in some atropine-treated cats. The time course of spikes in cats with electrolytic lesions of the caudate exhibited an increase in both frequency and duration. The results indicate that there is an optimal parameter for caudate stimulation causing inhibition of penicillin-induced hippocampal spiking activity, and suggest the possibility of tonic control of hippocampal excitability exerted by the caudate nucleus.     

Histaminergic mechanisms in experimental convulsions

Effect of some histamine (HA) agonists and antagonists were assessed on electroshock (MES) convulsions in mice and rats. In mice, pretreatment with the HA precursor, l-histidine (100, 500 and 1000 mg/kg) precipitated seizures after a subthreshold (30 mA) stimulus. Both incidence (%) and tonic hind limb extensor phase (THE) were more than that in vehicle treated controls. The H1 blockers, pheniramine (25 mg/kg) and promethazine (25 mg/kg) both protected against (60 mA) MES and both incidence of convulsions and THE were reduced. A similar protective effect was not seen with either the H2 blocker, cimetidine (up to 200 mg/kg), or atropine (1 mg/kg). In rats, both the classical antihistamines blocked MES seizures, whereas, the H2-blocker, cimetidine, and atropine were, ineffective. Further, both H1 blockers were ineffective in antagonizing seizures induced by pentylenetetrazole, INH, caffeine or strychnine. These results are discussed in light of a possible HA-ergic regulation of experimental convulsions.     

Sensitivity of spontaneously epileptic rats to external stimuli that induce seizures

The sensitivity of spontaneously epileptic rats (SER), double homozygotes of zitter and tremor mutations, to external stimuli that induce seizures was studied in comparison with tremor (tm/tm) and zitter (zi/zi) rats, and with normal Kyo: Wistar and F 344/N rats. Touching their body, a blinking light (1200 lux, 1 sec interval) or a big sound (8 and 12 kHz, 95 dB) induced tonic extension only in the SER. The response frequency was 22 to 44% at 9 weeks of age and 75 to 100% at 13 weeks of age. Electric stimulus at 30 mA induced tonic-clonic convulsions in all Kyo: Wistar and F 344/N rats. At 20 mA the incidence of seizures decreased with age, from 100% at 5 weeks of age to 33% at 13 weeks of age in Kyo: Wistar rats and from 100 to 71% in F344/N rats. In SER, 10-mA stimuli induced tonic extension at 9 and 13 weeks of age, and 20 and 30 mA induced tonic convulsions, generalized or partial convulsions, and wild jumping or running episodes at 5, 9 and 13 weeks of age. At 30 mA, the incidence of convulsive seizures decreased with age in both tremor (tm/tm) and zitter (zi/zi) rats. Apparently external stimuli acted as simple triggers in the induction of tonic extension, since characteristic tonic extension is induced in the SER by each of the stimuli used in the present study, and induced convulsions closely resembled spontaneously occurring convulsions. The threshold of external stimuli in the induction of tonic extension became lower with aging in the SER, indicating that they are appropriate models for evaluating anticonvulsant drugs, as reported previously.     

Cardiac neural discharge and epileptogenic activity in the cat: An animal model for unexplained death

This study developed an animal model to explore the hypothesis that altered automatic function may be one cause for unexplained sudden epileptic deaths. After α-chloralose anesthesia, 9 cats received a tracheostomy and a thoracotomy. Intravenous gallamine was used to paralyze the cats. Blood pressure, arterial blood gases, electrocardiogram, and rectal temperature were monitored. Simultaneous monitoring of the neural discharge in postganglionic cardiac sympathetic branches and the vagus nerve was combined with a bilateral craniectomy and electrocorticography. Pentylenetetrazol was given intravenously at 10 min intervals in 10, 20, 50, 100, 200, and 2000 mg/kg doses. Epileptiform discharges were categorized as a prolonged ictal (duration of 10 sec or more), brief ictal (duration of less than 10 sec mixed with suppression), and interictal spike activity. The two types of ictal activity were quantified by duration in seconds for the 10 min interval after each dose of pentylenetetrazol; the number of interictal spikes/min was determined for each minute of the entire experiment. This study developed a model which quantified the degree of epileptiform activity and correlated it with changes in cardiovascular function and autonomic cardiac neural discharge. An imbalance within and between sympathetic and parasympathetic cardiac neural discharges was found, as was a significant disruption of the physiological relationships between heart rate and blood pressure. Frequent and varied electrocardiogram abnormalities occurred. All of the above changes occurred during minimal (interictal) subconvulsant as well as during maximal (ictal) convulsant epileptogenic activity.     

METABOLIC RESPONSE TO FOCAL PENICILLIN SEIZURES IN RAT: SPIKE DISCHARGE VS. AFTERDISCHARGE1

Abstract– The correlations among clinical events, electrocorticogram, histology, size of focus, and biochemical changes were examined in a model of focal penicillin seizures in rats. Ten units of penicillin injected into the motor cortex were found to be the threshold dose for producing repetitive spike discharges. These were associated with synchronous contralateral muscle jerks which reached a peak intensity in 10 min and fell off rapidly in 45–90 min. The half-life of penicillin in the cortex was 15 min, with little diffusion from the site of injection. The size of the metabolic focus was determined by autoradiography with [2-¹⁴C]deoxyglucose and was 6.5 times larger than the diffusion of penicillin. Increased glucose utilization appeared in the focus and in cortical columns in the contralateral homo-typic cortex. Thirty times more penicillin (>300 units) was required to produce spikes with afterdischarge than to product spikes alone. Afterdischarges correlated with contralateral tonic-clonic seizures and occurred only after 1 h of exposure to penicillin. These lasted 10-45 s each and recurred over 3 to 4h. The size of the metabolic focus determined by [2-¹⁴C]deoxyglucose during afterdischarges was 4.6 times larger than the focus exhibiting spike discharges alone. Tissue substrates were measured in the seizure focus, homotypic ‘mirror’ cortex, and cortex remote from the focus in paralyzed ventilated animals. During repetitive spike discharge there was a fall in high energy compounds in the focus (phosphocreatine, 4.91 → 4.24 mmol/kg; ATP, 2.62 → 2.17 mmol/kg) and a rise in lactate (1.41 → 2.79 mmol/kg). Changes were similar but less intense in ‘mirror’ and remote cortex. During spikes with afterdischarge, changes in high energy compounds in the focus were of a similar magnitude (phosphocreatine, 4.91 → 3.86 mmol/kg; ATP, 2.62 → 2.46 mmol/kg) but there was a greater rise in lactate (1.41 → 6.32 mmol/kg) and a fall in glucose (2.38 → 1.81 mmol/kg). In contrast, changes in ‘mirror’ and remote cortex during afterdischarges showed an increase in high-energy compounds.     

Responses of caudate neurons to acoustic stimulation in cats

Responses of 141 neurons of the caudate nucleus to acoustic stimuli — tones (500 and 2000 Hz) and clicks of different frequency (0.2 and 0.8/sec) and intensity (75, 80, 95 dB) — were recorded extracellularly in chronic experiments on cats. The responses recorded showed great variability with respect to character (phasic, tonic), structure (one or two phases of excitation), latent periods (from 7.5 to 300.0 msec), and burst discharge frequency (from 90 to 800 spikes/sec). Analysis of averaged poststimulus histograms and graphs of the dynamics of the responses showed that responses of 74% of neurons were much better expressed if less frequent stimuli were used: The regularity of the responses and the number of spikes in each response increased. Responses of neurons also increased and acquired a more distinct temporal structure if the intensity of the clicks increased. The character of responses to clicks and tones differed qualitatively in 17% of neurons studied: Phasic excitation arose in response to clicks, tonic changes in spike activity to tones. The particular features of responses of caudate neurons to acoustic stimulation with different parameters are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 588–595, November–December, 1980.     

Patterns of activity in the antennular motoneurones of the hermit crab Pagurus alaskensis (Benedict).

1. Using electromyogram recordings from the antennular muscles of intact animals and recordings from the antennular nerves of partially dissected preparations, the patterns of activity in specific antennular motoneurones have been described during antennular flicking and antennular withdrawal. 2. The slow extensor motoneurone A30S is active during flicking in addition to the phasic component of the antennular motor system (A30F, A31F and A32F). 3. The flexion phase of a flick is the result of a burst of variable duration and number of spikes within flexor motoneurones A31F and A32F. 4. The extension phase of a flick is the result of a burst of variable duration and number of spikes in extensor motoneurones A30F and A30S. 5. Extension-withdrawal and slow flexion-withdrawal reflexes, tonic flexion withdrawal and maintained flexion at the MS-DS joint usually result from activity in part of the tonic component of the antennular motor system:moto-neurones A30S, A31S and A32S. 6. Fast flexion-withdrawal reflexes result from a burst of spikes in motoneurone A31F-S which constitutes the phaso-tonic component of the antennular motor system. 7. During high-frequency activity (15-60/sec), reciprocity exists between the slow flexor motoneurones A31S and A32S and slow extensor motoneurone A30S.     

Possible mechanism of anticonvulsant effect of ketamine in mice

The study was designed to investigate the effect of ketamine on convulsive behaviour using maximal electroshock (MES) test. An attempt was also made to study the possible receptor mechanisms involved. MES seizures were induced in mice via transauricular electrodes (60 mA, 0.2sec). Seizure severity was assessed by the duration of tonic hindlimb extensor phase and mortality due to convulsions. Intraperitoneal administration of ketamine produced a dose-dependent (5-50 mg/kg) protection against hindlimb extensor phase. The anticonvulsant effect of ketamine was antagonized neither by naloxone (low as well as high doses) nor sulpiride, but was attenuated by haloperidol, a dopamine (D2)/sigma receptor antagonist. Co-administration of gamma-aminobutyric acid (GABA)-ergic drugs (GABA, muscimol, diazepam and baclofen) and N-methyl-D-aspartate (NMDA) receptor antagonist, dizocilpine (MK801) with ketamine facilitated the anticonvulsant action of the latter drug. In contrast, flumazenil, a benzodiazepine (BZD)-GABAA receptor antagonist, reversed the facilitatory effect of diazepam on the anti-MES effect of ketamine. Similarly, delta-aminovaleric acid (DAVA), antagonized the facilitatory effect of baclofen on anti-MES action of ketamine. These BZD-GABAergic antagonists, flumazenil or DAVA per se also attenuated the anti-MES effect of ketamine given alone. The results suggest that besides its known antagonistic effect on NMDA channel, other neurotransmitter systems i.e. sigma, GABAA-BZD-chloride channel complex and GABAB receptors may also be involved in the anti-MES action of ketamine.     

Role of the catecholaminergic mechanisms and of the caudate nucleus in the development of generalized convulsions caused by the parenteral administration of penicillin]

In freely moving cats the behavioral and EEG-shifts, accompanied by myoclonic jerks with slow negative waves and spike-wave complexes in the cortexand caudate nucleus, were recorded following a single intramuscular injection of high penicillin doses. The stimulants of catecholaminergic transmission (L-DOPA and apomorphine) inhibited the development of such phenomena but facilitated origination of tonicoclonic cramps. The inhibitors of catecholaminergic synapses (aminazin and haloperidol) exerted reverse effects. The electrolytic injury to the caudate nucleus head also prevented formation of petit mal-like seizures while the threshold low-frequency stimulation of the nucleus increased penicillin effect.     

Tonic impulsation in preganglionic and postganglionic sympathetic fibers of mammals

A study of the tonic electrical activity of nerves containing preganglionic and postganglionic fibers in the superior cervical and stellate sympathetic ganglia of cats and rabbits has shown that this activity consists of groups of spikes synchronous with the pulse or respiration, and occurs on a background of irregular low-amplitude impulses. The frequency of spikes is higher (250/sec) in nerves containing preganglionic fibers than in those containing postganglionic fibers (100/sec). Groups of spikes in a nerve containing preganglionic fibers correspond in some preparations to groups of spikes of lower frequency in a nerve containing postganglionic fibers of the same ganglion; in other preparations, this correspondence was lacking, apparently due to the absence of synaptic contacts between those groups of pre- and postganglionic neurons whose activity was recorded. Neurons send axons to different nerves (cardiac and vertebral) of the stellate ganglion discharged synchronously in some preparations, and asynchronously in others. Where synchronization was observed, the neurons discharged in rhythm with cardiac contractions.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 303–308, November–December, 1969.     

Peripheral and central nervous responses evoked by small water movements in a cephalopod

Potentials were recorded from the epidermal head lines and from the CNS of young cuttlefish, Sepia officinalis, in response to weak water movements. 1. Within the test range 0.5-400 Hz a sinusoidal water movement elicits up to 4 components of response if the electrode is placed on a headline: (i) a positive phasic ON response; (ii) a tonic frequency-following microphonic response; (iii) a slow negative OFF response; and (iv) compound nerve impulses. 2. The amplitude of both the ON wave and the microphonic potential depends on stimulus frequency, stimulus amplitude and stimulus rise time. Frequencies around 100 Hz and short rise times are most effective in eliciting strong potentials. The minimal threshold was 0.06 microns peak-to-peak water displacement at 100 Hz (18.8 microns/s as velocity). 3. Change of direction of tangential sphere movement (parallel vs. across the head lines) has only a small effect on the microphonic and the summed nerve potentials. 4. Frequency and/or amplitude modulations of a carrier stimulus elicit responses at the onset and offset of the modulation and marked changes in the tonic microphonic response. 5. Evoked potentials can be recorded from the brain while stimulating the epidermal lines with weak water movements. The brain potentials differ in several aspects from the potentials of the head lines and show little or no onset or offset wave at the transitions of a frequency and amplitude modulation.     

Temporal threshold and response bias in the discrimination of empty intervals by cats

Cat's differential duration threshold was investigated by the method of limits in a schedule of discrimination of empty durations. The standard stimulus was 4 sec long throughout the experiment. The comparison stimulus was reduced from 10 to 5 sec by 1 sec steps in successive blocks of 5 sessions. Standard and comparison stimuli, delimited by 50 msec auditory signals, were equiprobably distributed, in a random sequential order of presentation in each trial. After a 2 sec delay, an auditory signal indicated that reinforcement was available upon a response on one of two levers. Weber fractions around .25 were obtained. Strong response bias developed in most cats. Some consequences of the inhibition of responding induced by the procedure were considered.     

The Characterization of Childhood Occipital Epilepsy of Gastaut: A Study of Seven Patients

Characterization of the electroclinical features and evolution of childhood occipital epilepsy of Gastaut (COE-G). Seven children were retrospectively identified as having COE-G and were followed-up clinically using EEGs. Visual manifestations were the most common ictal event. Eye-associated ictal deviation was associated with ipsilateral turning of the head and migraine-like symptoms were frequent. Hemiconvulsions occurred in two children, and only one child had secondary generalized tonic–clonic seizures. In all patients, seizures occurred while awake, while two patients also had seizures while sleeping. EEG showed five patients with occipital spike-wave discharges when their eyes were closed which disappeared once their eyes were opened. Two cases continued having frequent seizures despite antiepileptic drug treatment. These patients also displayed learning difficulties and behavioral impairments after seizure onset. COE-G is a distinctive epileptic syndrome; however, the long-term prognosis for patients with the condition is unclear.     

Time-dependence of SI RA neuron response to cutaneous flutter stimulation

Spike discharge activity of RA-type SI cortical neurons was recorded extracellularly in anesthetized monkeys and cats. Multiple applications (trials) of 10-50 Hz sinusoidal vertical skin displacement stimulation ("flutter") were delivered to the receptive field (RF). Analysis revealed large and systematic temporal trends not only in SI RA neuron responsivity (measured as spikes/s and as spikes/stimulus cycle), but also in entrainment, and in phase angle of the entrained responses. In contrast to SI RA neurons, the response of RA skin afferents to comparable conditions of skin flutter stimulation exhibited little or no dynamics. The occurrence and form of the SI RA neuron response dynamics that accompany skin flutter stimulation are shown to depend on factors such as stimulus frequency and the locus of the recording site in the global cortical response pattern. Comparison of recordings obtained in near-radial vs tangential microelectrode penetrations further reveals that the SI RA neuron response dynamics that occur during skin flutter stimulation are relatively consistent within, but heterogeneous across column-sized regions. The observed SI RA neuron response dynamics are suggested to account, in part, for the improved capacity to discriminate stimulus frequency after an exposure ("adaptation") to skin flutter stimulation (Goble and Hollins, J Acoust Soc Am 96: 771-780, 1994). Parallels with recent proposals about the contributions to visual perception of short-term primary sensory cortical neuron dynamics and synchrony in multineuron spike activity patterns are identified and discussed.     

Time-dependence of SI RA neuron response to cutaneous flutter stimulation

Spike discharge activity of RA-type SI cortical neurons was recorded extracellularly in anesthetized monkeys and cats. Multiple applications (trials) of 10-50 Hz sinusoidal vertical skin displacement stimulation ("flutter") were delivered to the receptive field (RF). Analysis revealed large and systematic temporal trends not only in SI RA neuron responsivity (measured as spikes/s and as spikes/stimulus cycle), but also in entrainment, and in phase angle of the entrained responses. In contrast to SI RA neurons, the response of RA skin afferents to comparable conditions of skin flutter stimulation exhibited little or no dynamics. The occurrence and form of the SI RA neuron response dynamics that accompany skin flutter stimulation are shown to depend on factors such as stimulus frequency and the locus of the recording site in the global cortical response pattern. Comparison of recordings obtained in near-radial vs tangential microelectrode penetrations further reveals that the SI RA neuron response dynamics that occur during skin flutter stimulation are relatively consistent within, but heterogeneous across column-sized regions. The observed SI RA neuron response dynamics are suggested to account, in part, for the improved capacity to discriminate stimulus frequency after an exposure ("adaptation") to skin flutter stimulation (Goble and Hollins, J Acoust Soc Am 96: 771-780, 1994). Parallels with recent proposals about the contributions to visual perception of short-term primary sensory cortical neuron dynamics and synchrony in multineuron spike activity patterns are identified and discussed.     

A multivariate population density model of the dLGN/PGN relay

Using a population density approach we study the dynamics of two interacting collections of integrate-and-fire-or-burst (IFB) neurons representing thalamocortical (TC) cells from the dorsal lateral geniculate nucleus (dLGN) and thalamic reticular (RE) cells from the perigeniculate nucleus (PGN). Each population of neurons is described by a multivariate probability density function that satisfies a conservation equation with appropriately defined probability fluxes and boundary conditions. The state variables of each neuron are the membrane potential and the inactivation gating variable of the low-threshold Ca²⁺ current I_T. The synaptic coupling of the populations and external excitatory drive are modeled by instantaneous jumps in the membrane potential of postsynaptic neurons. The population density model is validated by comparing its response to time-varying retinal input to Monte Carlo simulations of the corresponding IFB network composed of 100 to 1000 cells per population. In the absence of retinal input, the population density model exhibits rhythmic bursting similar to the 7 to 14 Hz oscillations associated with slow wave sleep that require feedback inhibition from RE to TC cells. When the TC and RE cell potassium leakage conductances are adjusted to represent cholingergic neuromodulation and arousal of the network, rhythmic bursting of the probability density model may either persists or be eliminated depending on the number of excitatory (TC to RE) or inhibitory (RE to TC) connections made by each presynaptic cell. When the probability density model is stimulated with constant retinal input (10–100 spikes/sec), a wide range of responses are observed depending on cellular parameters and network connectivity. These include asynchronous burst and tonic spikes, sleep spindle-like rhythmic bursting, and oscillations in population firing rate that are distinguishable from sleep spindles due to their amplitude, frequency, or the presence of tonic spikes. In this context of dLGN/PGN network modeling, we find the population density approach using 2,500 mesh points and resolving membrane voltage to 0.7 mV is over 30 times more efficient than 1000-cell Monte Carlo simulations. Action Editor: David Golomb     

Effects of duration of convulsions on energy reserves of the brain

Abstract— Rapid administration (0·4 ml in 1 sec) of the convulsant inhalant, flurothyl (hexafluorodiethyl ether, indoklon), to mice induced within 10 sec clonic-tonic seizures that were accompanied by marked decrease of P-creatine, decrease of ATP and glucose, and increase of lactate in the cerebral cortex. In contrast, mice to which flurothyl had been administered slowly (0·05 ml every 30 sec for 10 min) exhibited myoclonic jerks after about 3 min, merging into irregular clonus at about 5 min, and intermittent clonus thereafter until onset of tonic hind limb extension at about 10 min. In these mice, P-creatine in cerebral cortex decreased gradually for 6 min and then remained through 10 min at levels nearly as low as those reached 10 sec after rapidly administered flurothyl. Lactate in cerebral cortex increased much more during the 10 min of slow administration of flurothyl than in 10 sec of rapid administration, the greatest increase occurring at 4–6 min, as myoclonic jerks merged into irregular clonus. Glucose and ATP in cerebral cortex fluctuated somewhat but did not decrease greatly when flurothyl was administered slowly.     

Frequency and site-dependent variations in vibration detection thresholds on the face

An adaptive psychophysical procedure was used to estimate the vibration detection threshold at seven spatially matched sites on the two sides of the face and at one scalp site. Repeated measurements over six testing sessions were made for stimuli vibrating at 1, 10 and 100 Hz for each of 21 neurologically healthy, young adult females. Approximately 14 stimulus trials were required to obtain each estimate of the threshold amplitude. Thresholds varied as a function of frequency ( p < 0.0001), side ( p < 0.001) and site ( p < 0.0001). Compared to stimulation at 100 Hz at which the estimates were lowest, thresholds were 3.1 times greater at 10 Hz and 5.4 times greater at 1 Hz. Thresholds were lowest on the vermilion and highest on the cheek and chin. The preauricular skin and scalp exhibited an intermediate level of sensitivity. Whereas thresholds were comparable on the two sides of the face for stimulation at 1 Hz, they averaged 1.33 times greater on the right side for stimulation at 10 and 100 Hz. Moreover, thresholds obtained during the last two sessions were 16% higher than those obtained during the first two sessions ( p < 0.02), suggesting that subjects on average became more conservative in reporting the presence of the stimulus. The sensitivity in discriminating differences in tactile function favors use of the rapidly administered testing procedure in a clinical setting.     

Frequency and site-dependent variations in vibration detection thresholds on the face

An adaptive psychophysical procedure was used to estimate the vibration detection threshold at seven spatially matched sites on the two sides of the face and at one scalp site. Repeated measurements over six testing sessions were made for stimuli vibrating at 1, 10 and 100 Hz for each of 21 neurologically healthy, young adult females. Approximately 14 stimulus trials were required to obtain each estimate of the threshold amplitude. Thresholds varied as a function of frequency (p < 0.0001), side (p < 0.001) and site (p < 0.0001). Compared to stimulation at 100 Hz at which the estimates were lowest, thresholds were 3.1 times greater at 10 Hz and 5.4 times greater at 1 Hz. Thresholds were lowest on the vermilion and highest on the cheek and chin. The preauricular skin and scalp exhibited an intermediate level of sensitivity. Whereas thresholds were comparable on the two sides of the face for stimulation at 1 Hz, they averaged 1.33 times greater on the right side for stimulation at 10 and 100Hz. Moreover, thresholds obtained during the last two sessions were 16% higher than those obtained during the first two sessions (p < 0.02), suggesting that subjects on average became more conservative in reporting the presence of the stimulus. The sensitivity in discriminating differences in tactile function favors use of the rapidly administered testing procedure in a clinical setting.