L.C. Massopust

Evoked responses in the auditory cortex of the squirrel monkey

Abstract Using a semimacroelectrode, the contralateral and ipsilateral surface auditory cortices and insular cortices were mapped using 500 Hz 4-cycle “click” stimuli. The evoked responses were largest in amplitude and shortest in latency in the contralateral insular cortex. The crest of the contralateral superior temporal gyrus had the next highest amplitude and the next shortest latency. These two areas were considered as primary auditory input regions. The secondary areas consisted of the superior bank of the sylvian fissure lying within the precentral and postcentral gyri and the inferior temporal gyrus. The contralateral auditory surface cortex, based on the extent of evoked potentials recorded, was twice as large as the ipsilateral auditory cortex.

Electrical activity of the isolated macaque brain

Abstract The completely isolated brain (vascular as well as neurologic isolation) on donor perfusion showed excellent electrical activity of the cortex and reticular formation during all phases of its preparation including 1–4 hours of donor perfusion. As the various cranial nerves and spinal cord connections were severed from the brain stem, faster moderate voltage electrical activity appeared in cortex and reticular formation. These results were found in isolated preparations where no difficulties occurred in maintaining proper blood pressure, with minimal blood loss, and normothermic brain temperature. The neurogenically isolated brain (all cranial nerves severed) was maintained with little difficulty and appeared to show electrocortical activity similar to that in the completely isolated brain. Fast electrical activity appeared after the removal of the cranial nerves and spinal cord. Control of blood pressure, blood loss, and brain temperature was a prerequisite for optimum cortical activity. Severance of the brain stem between the mesencephalon and diencephalon (cervean isole) created first: a short period of synchronized slowing of electrical activity, followed by a longer period of extremely fast, low-voltage, desynchronized activity, then by phasic slow and fast activity. The intervals of slow activity increased in number and duration as the blood pressure became difficult to maintain, finally becoming very slow with high-voltage activity in the failing preparation. It appears that the isolated primate brain shows a range of electrophysiological activity including states characteristic of the aroused brain of an intact monkey.

Tolerance to arrest of cerebral circulation in the rhesus monkey

Abstract Twenty rhesus monkeys (Macaca mulatta) were subjected to periods of arrest of cerebral blood flow varying from 4 to 15 min. Arrest was accomplished by placing ligatures around the carotid and vertebral arteries. A drainage cannula in one carotid artery served to remove blood reaching the circle of Willis via anastomotic routes. After clamping the vessels, electrocortical activity (EEG) ceased within 25 sec. After reestablishment of blood flow to the brain, the EEG reappeared anywhere from 30 min to 5 hr depending on the duration of the arrest period. Animals subjected to periods of cerebral arrest up to 13 min showed no neurologic or behavioral deficits on the second postoperative day. The animal subjected to 14-min arrest retained motor deficits even 2 months postsurgically. Three animals subjected to 15 min of arrest failed to survive. One of these lived for 20 hr, recovering normal EEG activity and consciousness. It was able to make uncoordinated body and limb movements, but could not sit or eat. Controlled cerebral arrest up to 12 or 13 min appears to be relatively safe in the primate. Periods longer than this result in permanent neurologic deficits or death.

Cortical and subcortical responses to hypothermia

Abstract The purpose of this study was to compare the effects of induced hypothermia on cortical and subcortical spontaneous electrical activity under two barbiturates and one muscle relaxant. Cats with cortically and subcortically implanted recording electrodes were given either sodium pentobarbital, sodium thiamylal, or gallamine triethiodide, and then hypothermia was induced by means of subtotal body cooling. Under the barbiturates, cortical and subcortical slow-wave activity was preserved until low intracerebral temperatures had been reached, at which time all activity tended to become isoelectric. However, under the muscle relaxant, cortical low-voltage fast activity was present at a readable level at low intracerebral temperatures. The most striking finding was the preservation of anterior reticular-formation activity at an excellent level at low intracerebral temperatures. It was the last brain stem region affected by hypothermia and the first to fully recover its precooling level of activity.

Changes in auditory frequency discrimination thresholds after temporal cortex ablations

Abstract Male monkeys (Macaca mulatta) were trained to discriminate two tones at 500 and 1000 Hz (cycle/sec) following normal conditioned avoidance procedures. At 500 and 1000 Hz a criterion of 90% correct response (CR) was required of each subject. The 1000-Hz tone was then reduced through a series of steps until 503 Hz was reached. All subjects were able to discriminate at 5-Hz separation of the two tones well above threshold (75% CR). At this point, bilateral ablation of portions of the primary and associated auditory cortices was performed. The animals were allowed to recover for 7 days, then were retested using the same discrimination procedure. Bilateral ablation of various portions of the postcentral gyrus, the superior temporal gyrus and the insular cortex caused varying increases in discrimination thresholds. One animal in which the ventral half of the superior temporal gyrus and the ventral limb of the insular cortex lying deep to the sylvian fissure were destroyed showed an increase in frequency discrimination threshold of only 7 Hz. On the other extreme, one animal in which the entire superior temporal gyrus and the extreme inferior portion of the postcentral gyrus were removed in depth showed an increase in threshold of between 25 and 30 Hz. This lesion included about 40% damage to the insular cortex. The remaining subjects exhibited increases in thresholds lying between 7 and 20 Hz depending upon the location and amount of damage to the superior temporal gyrus. Evoked auditory potentials were recorded from the viable cortex surrounding the lesions and typical surface response maps were constructed for each animal.

Electroencephalographic characteristics of brain cooling and rewarming in monkey.

Abstract Monkeys were subjected to extracorporeal autocerebral perfusion hypothermia. Half of the animals were containuously perfused after brain temperature reached 15 C for 30 min. The other half were subjected to circulatory arrest for 30 min after intracerebral temperatures fell to 15 C. In either case, the electroencephalogram showed a gradual decrease in the amplitude of the major frequency, followed by a loss of the major frequency, then a decrease in amplitude of the minor frequency with continuous slowing. Finally, low amplitude theta frequencies only were present; these became isoelectric at intracerebral temperatures of 22-19 C. It took about 35 min to cool the brain from 37 to 15 C. On rewarming, but before recovery of the animal, it took approximately 3 hours before the EEG activity approached prehypothermic frequencies and amplitudes with intracerebral temperatures reaching 34 C within 25 min after initiation of rewarming. Cerebral blood flow changes and changes in cellular membrane permeability probably contribute to the long latency in return of EEG activity.

Spontaneous electrical activity of the brain in hibernators and nonhibernators during hypothermia

Abstract During induced hypothermia, electrical activity recorded from the cerebral cortex of nonhibernators (cat and guinea pig) and hibernators (prairie dog and ground squirrel) gradually fell to the isoelectric point at 25C esophageal or buccal temperature in the nonhibernators and 17C in the hibernators. Electrical activity in the mesencephalic reticular formation remained at good amplitudes to about 23C esophageal and buccal temperature in the cat and guinea pig, and was still present at 16C in the prairie dog and ground squirrel. Cats and guinea pigs did not rewarm if their esophageal temperatures fell below 24C. Even at 25C it was necessary to apply resuscitation technics and direct heart warming to recover the animal. Prairie dogs and ground squirrels rewarmed, after their esophageal temperatures dropped below 16C, without resuscitation and heart warming. The sustained electrical activity observed in the anterior reticular formation of hibernators below 16C buccal temperature suggests a special mechanism for the maintenance of minimal metabolic conditions and circulatory integrity at reduced body temperature.

Striate cortex-superior colliculus projection in squirrel monkey

Abstract The corticofugal projections from the striate cortex to the superior colliculus in the squirrel monkey were electrophysiologically investigated. The cortical afferents projected to the ipsilateral superior colliculus in a point-to-point manner and were retinotopically organized. They terminated mainly in the deep layer of the stratum griseum superficiale, the stratum opticum, and the superficial layer of the stratum griseum intermediale. In these layers photic collicular units were mostly sensitive to moving objects. Convergence of afferent pathways from the retina and striate cortex on collicular neurons could not be demonstrated.

Arrest of cerebral blood flow and reperfusion of the brain in the rhesus monkey

Abstract Rhesus monkeys were subjected to cerebral ischaemia by arresting blood flow to the brain. The carotid and vertebral arteries were temporarily occluded and a cannula inserted into one common carotid artery permitted retrodrainage of blood reaching the circle of Willis via anastomotic channels. The blood from the cerebral vessels was washed out with dextran solution for photographic recording of the arrest of cerebral blood flow and subsequent reperfusion of the cerebral vasculature. Electroencephalographic, cardiovascular and respiratory functions were monitored throughout the procedure. Occlusion of the four major vessels with retrodrainage of the circle of Willis effectively stops perfusion of the brain. Occlusion of the vessels without retrodrainage permits a slow but significant flow of blood to the cerebral vessels. Rapid and effective reperfusion of the brain was noted even after repeated and lengthy periods of ischaemia. Thus a model for studying cerebral ischaemia, and reperfusion after ischaemia, without major thoracic or intracranial intervention is demonstrated. Some implications for resuscitation in cases of cerebral ischaemia are discussed.

The effect of hypoxia on electrocortical activity in the cebus monkey

Abstract Cebus monkeys were subjected to 8, 6, 4, and 2% inspired oxygen concentrations in nitrogen to create conditions of hypoxia without complete anoxia, cardiac arrest, asphyxia, or vascular occlusion of blood supply to the brain. The ECoG, EKG, and arterial blood oxygen saturations were examined before, during, and after a 30-min period of hypoxia. The ECoG changes in the 8% hypoxic group followed the course of events described below and were reversible: (a) The prehypoxic ECoG, recorded from the precentral and post-central gyri, consisted of high amplitude 5–7 Hz activity with 15–20 Hz activity superimposed and interposed; (b) loss of the 15–20 Hz activity; (c) reduction in amplitude of 5–7 Hz activity; (d) appearance of short isoelectric periods; (e) appearance of spindle-burst activity; (f) lengthening of isoelectric periods and disappearance of spindle bursts; and (g) complete loss of activity (isoelectric). The 4 and 6% hypoxic groups followed the same course of events described above except that the loss of 15–20 Hz occurred much more rapidly, the appearance of spindle-burst activity was extremely transient, and the isoelectric periods lengthened rapidly. In the 2% hypoxic group all ECoG events occurred precipitously, reaching the isoelectric phase within 7 min. Since these animals suffered cardiac arrest, only 9 min of hypoxia was possible before the recovery phase was instituted. The cardiac picture (EKG) during the hypoxic interval showed evidence of right and left bundle branch block and arrhythmia. In some animals of the 4 and 2% hypoxic groups evidence of cardiac ischemia and arrest was noted. The percentage of oxygen saturation of blood in the 8% hypoxic group dropped to and leveled off at an average of approximately 48% in 3 min, approximately 36 and 18% in 1 min for the 6 and 4% hypoxic groups, respectively, and “off-scale” on the oximeters in 10–15 sec in the 2% hypoxic group.