Prolonged changes in visual system activity produced by somatic stimulation

Rapid eye movement (REM) sleep and ponto-geniculo-occipital (PGO) spike density are increased by somatic stimulation

It has been shown that REM sleep duration and ponto-geniculo-occipital (PGO) spike density can be enhanced by auditory stimulation. The purpose of this study was to determine whether this effect is restricted to the auditory sensory modality or whether somatic stimulation can produce similar effects. Cats implanted with electrodes for recording the sleep-wake cycle were additionally prepared with clip electrodes placed in the neck for somatic stimulation. Such stimulus was applied at the beginning and throughout each REM sleep period. The effect of this procedure was compared to a similar period when no stimulus was applied. The results showed that somatic stimulation induced a significant increase in REM duration (60.2%) and PGO spike density. Since the effects of somatic stimuli are identical to auditory ones, it is suggested that all sensory modalities may share the property of influencing the mechanisms which regulate the maintenance of REM sleep. Such mechanisms are discussed in terms of an increase in the excitability levels of polymodal medial reticular neurons.

Increasing PGO spike density by auditory stimulation increases the duration and decreases the latency of rapid eye movement (REM) sleep

The purpose of this study was to determine whether ponto-geniculo-occipital (PGO) spikes play a role in triggering or maintaining sleep. During the recording of the sleep cycle of cats, the appearance of the first PGO spike automatically triggered an auditory stimulus through a speaker placed in the cat's recording cage. The effect of this procedure was compared to similar period when no such stimulus was given. The results showed that the auditory stimulus increased PGO spike density during REM sleep. It also produced a spectacular increase in the duration of REM, while decreasing the latency of its appearance from the first PGO spike. It is suggested that the auditory stimulus reinforces the 'PGO system', which in turn may function as a pace-setter for priming and maintaining REM sleep.

Auditory evoked phosphenes in optic nerve disease

Five patients with optic neuropathy, four vascular and one demyelinating, are described who each complained of an unusual symptom. Bright flashes of light (phosphenes) occurred in the affected eyes and were evoked by sudden unexpected sounds. Movement of the eye alone did not reproduce the symptom. In all patients the phenomenon was sufficiently prominent to interfere with sleep and was the main complaint of one patient. An anticonvulsant (phenytoin) greatly reduced the frequency and intensity of the phosphene in one patient.

Relationship of geniculate and occipital PGO waves and the effects of nonvisual sensory activity

The nature of occipital PGO waves (REM) was addressed by comparing the occipital PGO waves measured at the marginal gyrus with the geniculate PGO waves and the occipital PGO waves "directly" transmitted to the occipital cortex. The directly transmitted PGO waves lack the first short positive-going spike that precedes the negative phase of the occipital PGO waves. The "directly" transmitted PGO wave was recorded from cats with either deafferented or excised LG nucleus. The "directly" transmitted PGO wave resembled pontine negative-going PGO wave more regarding amplitude and wave shape changes than the occipital PGO waves of intact cats. The ascending negativity of pontine PGO waves is indirectly transmitted through phasic increase of the local excitatory processes, more in the LG than in the occipital cortex. The PGO waves seem to be affected by endogenous and exogenous nonvisual processes, more in the LG than the occipital cells alone. The occipital PGO waves seem to result from the vectorial sum of geniculate and "directly" transmitted occipital PGO waves.

Acetylcholine and somatically evoked inhibition on perigeniculate neurones in the cat

1 Perigeniculate neurones in cats were found to be inhibited by iontophoretically applied acetylcholine (ACh) and some of them by somatic sensory stimulation under certain experimental conditions. 2 Under chloralose anaesthesia, perigeniculate neurones could be divided into two groups with regard to their spontaneous activity, sensitivity to glutamate and reaction to sensory inputs. Somatic sensory stimulation clearly inhibited the glutamate discharges of those perigeniculate neurones which were characterized by a high sensitivity to glutamate and the absence of spontaneous activity. ACh had no clear inhibitory effect. 3 Under fluothane and urethane anaesthesia, no somatic sensory influence was noticed but ACh depressed almost all perigeniculate neurones. 4 In an unanaesthetized midpontine pretrigeminal preparation, the inhibitory effect of ACh was confirmed. 5 No conditions were found which the inhibitory influences of ACh and those of somatic sensory stimulation could be observed simultaneously on the same neurone. Therefore, it could not be established whether ACh mediates the somatic sensory influences on perigeniculate cells.

Neurophysiological effects of dorsal column stimulation in man and monkey

✓ In 18 patients with cancer and intractable pain, capacitatively coupled pulses of 0.25 msec duration were delivered transcutaneously at 100 Hz to sets of five in-line electrodes implanted subdurally over the dorsal columns. Averaged somatosensory-evoked potentials were recorded from scalp electrodes before, during, and after application of current. All but one patient experienced relief of pain during stimulation, persisting for as long as several hours afterward. Eleven patients developed hyperactive deep reflexes, pathological reflexes, and decreased perception of joint rotation, pain, and touch below the level of current application. Somatosensory-evoked potential amplitudes were markedly reduced. All neurological findings returned to control values within 1 hour after each of repeated applications of current. Histological examination of spinal cord sections from four cancer patients showed no changes secondary to long-term current application.

Similar currents were applied to the spinal cord of 15 monkeys with chronically implanted bipolar recording or stimulating electrodes over the lower, middle, and upper thoracic cord, in nucleus ventralis posterior lateralis (VPL), and over the sensory motor cortex (SMC). With application of current, the responses in VPL and SMC to peripheral stimulation were abolished. Evoked potential responses were abolished between bipolar stimulating electrodes and bipolar recording electrodes separated by the five in-line electrodes used to supply the 100 Hz current. However, when both stimulating and recording electrodes were either above or below the five in-line electrode set, evoked responses were unaffected. The findings indicate that applied currents blocked neuronal transmission by producing local changes in the cord. The prolonged alteration of cerebral evoked potentials and relief of pain, however, could also be related to involvement of supraspinal neurons.

Polysensory interactions in the cuneate nucleus

1. The effects of light flashes or sound clicks on somatic sensory activity in the cuneate nucleus of the cat were studied. Polysensory interactions were demonstrated by means of gross potential recording in the cuneate nucleus or medial lemniscus, single unit recording in the cuneate nucleus, and excitability testing of tract terminals.2. Brief flashes or clicks were found to produce negative (N) and positive (P) waves in the cuneate nucleus similar to those produced by cutaneous stimulation. Furthermore, the P wave evoked by conditioning photic or acoustic stimuli depressed the P wave produced by cutaneous test stimuli.3. Conditioning photic or acoustic stimuli inhibited spontaneously firing cuneate neurones as well as those driven by cutaneous test stimuli.4. Conditioning photic or acoustic stimuli depressed the test discharge in the medial lemniscus evoked by cutaneous test stimuli.5. Micro-electrode stimulation within the cuneate nucleus evoked an antidromic response in the superficial radial nerve consisting of two spike complexes. Conditioning photic or acoustic stimuli caused an increase in the size of the initial spike complex and a depression in the secondary spike complex. These changes and the time courses of all the interactions observed were suggestive of presynaptic inhibition.6. The modulatory influences of photic and acoustic stimuli on the cuneate nucleus were present under alpha-chloralose or pentobarbitone anaesthesia and the acoustic influence persisted after midcollicular decerebration. When added to other evidence, the above findings suggest that the reticular formation of the brain stem plays an important role in these polysensory interactions.