Responses In Somatosensory Cortex Research Articles

Effect of morphine-induced cortical excitation on somatosensory responses evoked in the periaqueductal grey matter

The somatosensory cortex responses and periaqueductal grey matter responses evoked by electric peripheral nerve stimulation were studied following topical application of 1% morphine solution to the primary somatosensory area of rat cerebral cortex. Cortically applied morphine increased the negative component of cortical potentials and enhanced the peak-to-peak amplitude of the periaqueductal grey responses. It is suggested that cortical excitation induced by morphine generates descending bioelectrical impulses modulating neuronal activity at this mesencephalic level.

Optical mapping of electrical activity in rat somatosensory and visual cortex

We have investigated the use of optical methods for monitoring neuron activity in mammalian cortex. The cortex was stained with a voltage-sensitive dye and fluorescence was simultaneously measured from 124 areas using a photodiode array. Optical signals were detected in rat somatosensory cortex in response to small whisker movements and in visual cortex in response to light flashes to the eye. Relatively large signals were obtained during focal interictal epileptiform discharges induced by bicuculline. The measuring system had a time resolution of milliseconds and a spatial resolution of a few hundred micrometers. Simultaneous, multi-site optical recordings of activity may provide a new and potentially powerful method for studying function and dysfunction in mammalian cortex.

Variability of cortical evoked potentials to tooth pulp stimulation in unrestrained rats

In unrestrained adult rats evoked potentials were recorded by implanted electrodes in the somatosensory cortex in response to electrical stimulation of the pulp of an upper incisor. The spontaneous EEG, motor activity of the animal, and its respiratory movements were recorded simultaneously. Significant differences were observed in the configuration of the potentials and mean amplitude of the primary complex (P1+N1) during states of slow sleep, drowsiness, relaxed wakefulness, grooming, and investigative behavior; the amplitude of the primary complex during marked motor activity was reduced by more than an order of magnitude compared with that observed in a state of motor rest. In a state of relaxed wakefulness negative correlation was recorded between the amplitude of evoked potentials and momentary values of the respiration rate, weaker during periods of intensive motor activity. Meanwhile no direct parallel was observed between changes in potentials and respiration rate over the whole range of behavioral states studied: Depression of potentials was maximal during grooming whereas the respiration rate was maximal during investigative behavior.

Neurochemical mechanisms of participation of the caudate nuclei in food-getting behavior.

1. Stimulation of acetylcholinergic structures of CN by microinjections of carbachol and neostigmine caused inhibition of the motor component of the conditioned food-getting reflex. The conditioned orienting reaction to acoustic stimuli and also the natural food reflex were not affected under these conditions. 2. Injection of carbachol and neostigmine into the head of CN led to a decrease, whereas injection of atropine led to an increase in amplitude of the late components of EP in the motor and somatosensory areas of the cortex to conditioned acoustic stimuli. 3. Stimulation of the dopaminergic structures of CN by apomorphine caused facilitation of the food-getting conditioned reflex, whereas inhibition of dopaminergic structures of CN by haloperidol led to inhibition of this reflex. 4. Microinjections of dopamine and dopaminotropic agents into the head of CN had a much weaker effect on the food-getting conditioned reflex than neurochemical action on the acetylcholinergic structures of this nucleus. 5. Analysis of EP in the motor and somatosensory cortex in response to conditioned acoustic stimuli after administration of apomorphine and haloperidol revealed no antagonism between the acetylcholinergic and dopaminergic systems of CN. Apomorphine, like acetylcholinomimetics, caused a decrease, whereas haloperidol caused an increase in amplitude of the late components of EP.

Effect of motropine and naloxone on electroacupuncture analgesia

It was demonstrated in experiments on awake rabbits that electroacupuncture increases the pain threshold (the tail-flick-test) and suppresses the second positive wave of evoked potential in the somatosensory cortex in response to nociceptive electrocutaneous stimulation. Naloxone, the typical antagonist of narcotic analgetics, in doses of 0.05-0.1 mg/kg completely blocks the effects induced by electroacupuncture. The similar effects were produced by motropin, a new antagonist of narcotic analgetics, belonging to the tropan series, administered in doses of 10-20 mg/kg.

Latent periods and synchronization of unit discharges of the visual and somatosensory cortex in response to conditioning flashes

Latent periods and synchronization of unit discharges of the visual and somatosensory cortex in response to conditioning flashes

Action of strychnine on the specific somatosensory projection pathway

Subconvulsive doses of strychnine (0.08–0.1 mg/kg) greatly facilitated the primary cortical responses evoked in anaesthetized cat by low threshold cutaneous volleys. This facilitatory action was observed only when the afferent volleys passed through the first and the second synaptic relays of the spinocervical tract. If the testing afferent volleys did not pass through these synaptic relays (when stimuli were applied to the dorsal column, to the medial lemniscus or to the ventralis posterolateralis nucleus of the thalamus), subconvulsive doses of strychnine did not facilitate the primary responses in somatosensory cortex. It seems likely that the increase of the tactile sensitivity observed in man after the administration of the therapeutic doses of strychnine is also due to a facilitatory action of this drug mainly on the synaptic relays of the spinocervical tract.

Responses of human somatosensory cortex to stimuli below threshold for conscious sensation.

Averaged evoked responses of somatosensory cortex, recorded subdurally, appeared with stimuli (skin, ventral posterolateral nucleus, cortex) which were subthreshold for sensation. Such responses were deficient in late components. Subthreshold stimuli could elicit sensation with suitable repetition. The primary evoked response was not sufficient for sensation. These facts bear on the problems of neurophysiological correlates of conscious and unconscious experience, and of "subliminal perception."