Central Thalamus Research Articles

Thalamic center for the lateral line system in the catfish Ictalurus nebulosus: evoked potential evidence.

By means of evoked potential methods, a lateral line center in the thalamus of the bullhead catfish is here identified. The locus of this lateral line center corresponds to the mechanoreceptive thalamic zone and/or torothalamic tract identified by anatomical means. The thalamic lateral line area responds to acoustic stimuli as well as lateral line nerve shock but fails to respond to electroreceptor inputs that do cause responses in their special part of the midbrain torus semicircularis. The latency of the first peak of response to lateral line nerve shock, which is also the main response peak, is 30 ms for the thalamic zone compared to 15 ms for the earliest peak response in the mechanoreceptive part of the torus semicircularis. The thalamic response fatigues much more quickly than the toral response and has different dynamic properties to closely spaced stimulus pairs as well.

Diencephalic modulation of activities of raphe-spinal neurons in the cat

The modulatory effects of diencephalic stimulation on the activities of raphe-spinal neurons were studied extracellularly in cats. Among 240 raphe neurons recorded, 57 neurons were activated antidromically by stimulation of the cervical dorsolateral funiculus. These raphe-spinal neurons were found in the caudal raphe nuclei, i.e., the raphe magnus (43 neurons), raphe obscurus (11), raphe pallidus (2), and raphe pontis (1). All of them responded to innocuous and/or noxious peripheral mechanical stimuli with a broad receptive field. The activities of the majority of these neurons were facilitated by trains of pulse stimulation of the rostral periaqueductal gray and the thalamic relay nucleus but not of the thalamic center median nucleus. The facilitation of firing persisted for more than 3 min after the cessation of train pulse stimulation when the stimulation was applied at 20 Hz for 5 to 30 s. This facilitation was not affected by decortication of the sensorimotor area bilaterally. The facilitatory response to periaqueductal gray stimulation was markedly suppressed by systemic administration of naloxone. On the other hand, that of the thalamic relay nucleus stimulation was found to be unaffected. Based on these findings, the mechanisms of pain relief by stimulation of the rostral periaqueductal gray and thalamic relay nucleus reported in human intractable pain appear to relate, at least partly, to the activation of raphe-spinal neurons. However, the paths to raphe-spinal neurons of stimuli from the periaqueductal gray and the thalamic relay nucleus are thought to be independent from each other based on the different effects of naloxone.

The sleep cycle and subcortical-cortical EEG relations in the unrestrained chimpanzee

The sleep cycle and subcortical-cortical EEG relationships were studied in the unrestrained chimpanzee. Sleep was recorded for 7 consecutive nights from each of three chimpanzees by means of biotelemetry techniques. The animals averaged 6.5% of their total nocturnal sleep time in light sleep, 53.9% in medium sleep, 20.3% in deep sleep and 19.3% in rapid eye movement sleep (REM). The mean duration of the chimpanzees' sleep cycle was 86 min. A “first night effect” was evidenced by a lower percentage of REM, a higher percentage of light sleep, more time spent in the awake stage, and longer latencies to the onset of both deep sleep and REM. Computer analysis techniques were used in the description of the physical parameters of the EEG to investigate subcortical-cortical relationships during the various stages of the sleep cycle. During REM, non-REM and the awake stages of the cycle, the cortex and each subcortical area studied were found to have their own characteristic patterns of spectral density. The spectral density patterns of the ventral anterior thalamus and the midbrain reticular formation most resembled those of the cortex, whereas the patterns of the thalamic center median and hippocampus were least like those of the cortex. Coherences between subcortical areas and cortex were found to be either (a) higher during the stages of sleep than in the awake stage, as between the midbrain reticular formation and cortex; (b) higher during some stages of sleep but lower in others than in the awake stage, as between ventral anterior thalamic nucleus and cortex; or (c) relatively low in all stages of the cycle, as between the hippocampus and cortex. The unrestrained chimpanzee's sleep cycle as well as his subcortical-cortical EEG patterns were found to compare closely with those of man.

Relationship between Activity of Respiratory Center and EEG

This chapter discusses the relationship between activity of respiratory center and Electroencephalography (EEG). The EEG, electrical activity of the phrenic nerve and blood pressure were recorded simultaneously in cats immobilized with D-tubocurarine chloride under artificial respiration. The EEGs were recorded using bipolar electrodes from the anterior sigmoid gyrus, suprasylvian gyrus, caudate, preoptic area, amygdala, lateral hypothalamic nucleus, thalamic centre median, hippocampus, and midbrain reticular formation. In order to exclude the effects of ascending impulses on the reticular formation, the spinal cord was transected at the level of C 6 –C 7 , or the carotid body was denervated. In all cases, cessation of artificial respiration caused an arousal reaction in the EEG pattern of the neocortex and hippocampus. The periodic change in the EEG might possess a closer relationship with some of these activities than with the phrenic volley. It is found that the periodic EEG fluctuation of the neocortex did not occur in the same phase, as did the phrenic volley.

An Electrophysiologic Study of Ascending Pathways from Nucleus Caudalis of the Spinal Trigeminal Nuclear Complex

O BSERVATIONS originally made by Sjiiqvist al and confirmed by other neurosurgeons10,25,a0,ag,40 indicate tha t nucleus caudalis s,26 of the spinal trigeminal nuclear complex is an essential relay nucleus in the anatomic substrate subserving the conduction and integration of impulses evoked by noxious stimuli. I t follows tha t a thorough knowledge of the routes and terminals of afferent pathways extending from nucleus caudalis is necessary to the understanding of neural mechanisms involved in clinically recognized pat terns of pain. Anatomic studies 7,32,33 indicate tha t the pat tern of axonal trajectories emanating from nucleus caudalis differs from tha t of the more rostral components of the spinal trigeminal nuclear complex (nucleus interpolaris and nucleus oralis) and the main sensory nucleus. Furthermore, the soma of trigeminal fibers which project directly to the midbrain and thalamic centers associated with nociperception are contained only within nucleus caudalis. This report presents the findings of an electrophysiologic s tudy devised to identify midbrain and thalamic loci activated by a trigeminal input relayed primarily through nucleus caudalis and to compare these regions with brain-stem loci act ivated by impulses relayed at all levels of the trigeminal nuclear complex. The results of this investi-

CHICAGO NEUROLOGICAL SOCIETY

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VASCULAR CHANGES IN THE THALAMIC NUCLEI UNDERGOING RETROGRADE DEGENERATION

The different parts of the neocortex receive fibers from definite cell masses in the dorsal thalamus. Injury to a cortical area results in retrograde degeneration of the thalamic center the fibers of which end in the area destroyed. Associated with the degeneration of the nerve elements there occur profound vascular changes. This was first noticed in the dorsal nucleus of the lateral geniculate body after extirpation of the visual cortex.1The vascular changes consisted of enlargement of the afferent vessels, apparent increase in their number, thickening of the capillary network and heightened permeability of the vascular walls. The present study is an attempt to find whether there are such vascular changes in other thalamic nuclei after destruction of their respective cortical fields. I used albino rats as subjects. The projection of the thalamic centers on the cortex in this animal has been worked out by Lashley,2Clark,3

CENTRAL PAIN FROM LESIONS OF THE PONS

While pain and painful paresthesia have long been known as symptoms of thalamic disease, it always been a question amongneurologists whether these symptoms could occur from involvement of the central nervous system below the optic thalamus. The pain and uncomfortable paresthesia caused by disease of the thalamus, have been explained by most observers as being due to irritation of fibers of the sensory tracts, but Henry Head1believes that central pain is the result of setting the thalamic center, located in the medial nucleus, free from cortical control, with the result that it acts without restraint to all stimuli capable of arousing affective states. According to him the cortical sensory fibers end in the lateral nucleus, the region usually affected in cases exhibiting the thalamic syndrome. Head states that he has not found this over-response to stimuli, as well as spontaneous pain, from lesions of other parts of