Geniculate Stimulation Research Articles

Acoustic tone or medial geniculate stimulation cue training in the rat is associated with neocortical neuroplasticity and reduced akinesia under haloperidol challenge

Sensory cues can improve movement deficits in Parkinson's disease, but little is known about the mechanisms involved. To investigate neuroplastic changes following sensorimotor cue training, rats were shaped to respond to acoustic tone or medial geniculate stimulation cues by retrieving a food reward. Neuroplasticity associated with training was assessed by changes in auditory neocortical evoked field potentials and dendritic morphology. Stimulation cue training was associated with changes in dendritic arbour length and complexity in auditory and motor neocortices, but was without effect on evoked electrophysiological responses. Tone cue training was associated with a significant increase in peak height of the evoked auditory response and then under haloperidol challenge, demonstrated reduced akinesia. Results indicate that cue-training induces neuroplastic changes that may be related to improved sensorimotor function under dopaminergic antagonism.

Thalamic stimulation largely elicits orthodromic, rather than antidromic, cortical activation in an auditory thalamocortical slice

Stimulation of the medial geniculate body in an auditory thalamocortical slice elicits a short-latency current sink in the middle cortical layers, as would be expected following activation of thalamocortical relay neurons. However, corticothalamic neurons can have axon collaterals that project to the middle layers, thus, a middle-layer current sink could also result from antidromic activation of corticothalamic neurons and their axon collaterals. The likelihood of thalamic stimulation activating corticothalamic neurons would be reduced substantially if the corticothalamic pathway was not well preserved in the slice, and/or if the threshold for antidromic activation was significantly higher than for orthodromic activation. To determine the prevalence and threshold of antidromic activation, we recorded intracellularly from day 14–17 mouse brain slices containing infragranular cortical neurons while stimulating the medial geniculate or thalamocortical pathway. Antidromic spikes were confirmed by spike collision and characterized according to spike latency ‘jitter’ and the ability to follow a high-frequency (100 Hz) stimulus train. The ability to follow a 100-Hz tetanus was a reliable indicator of antidromic activation, but both antidromic and orthodromic spikes could have low jitter. Thalamic stimulation produced antidromic activation in two of 69 infragranular cortical neurons (<3%), indicating the presence of antidromic activity, but implying a limited corticothalamic connection in the slice. Antidromic spikes in 13 additional neurons were obtained by stimulating axons in the thalamocortical pathway. The antidromic threshold averaged 214±40.6 μA (range 6–475 μA), over seven times the orthodromic threshold for medial geniculate-evoked responses in layer IV extracellular (28±5.4 μA) or intracellular (27±5.6 μA) recordings. We conclude that medial geniculate stimulation activates relatively few corticothalamic neurons. Conversely, low-intensity thalamic stimulation strongly activates thalamocortical neurons. Thus, at low-stimulus intensities, the auditory thalamocortical slice can be used to probe mechanisms of thalamocortical function with limited antidromic activation of corticothalamic neurons.

Convergence of projections from the rat hippocampal formation, medial geniculate and basal forebrain onto single amygdaloid neurons: an in vivo extra- and intracellular electrophysiological study

We recorded extra- and intracellular responses from rat amygdaloid neurons in vivo after electrical stimulation of the hippocampal formation (dentate gyrus, hippocampal fields CA3 and CA4, entorhinal cortex, subicular complex); medial geniculate; and basal forebrain (diagonal band, ventral pallidum, olfactory tubercle, nucleus accumbens, bed nucleus of stria terminalis, lateral preoptic area, substantia innominata). Stimulation of hippocampal formation structures evoked IPSPs or EPSP-IPSP sequences in which the IPSP had a lower threshold than the EPSP. Recordings from candidate inhibitory neurons in the amygdala indicated that excitatory afferents from the hippocampal formation contact both amygdaloid inhibitory and principal neurons (feedforward inhibition), and that the inhibitory neurons have a lower threshold of activation. Medial geniculate stimulation also evoked EPSP-IPSP sequences. In marked contrast to these results, stimulation of basal forebrain structures evoked short latency IPSPs in amygdaloid neurons. This provides the first physiological evidence for direct inhibition of the amygdala by the basal forebrain. Basal forebrain stimulation also evoked EPSP-IPSP sequences in amygdaloid neurons. Individual amygdaloid neurons could show responses to stimulation of the hippocampal formation, basal forebrain, and medial geniculate, indicating that synaptic input from these areas converges onto single amygdaloid cells. The findings provide further information about the synaptic organization of afferents to the amygdala, and indicate that single amygdaloid neurons play a role in the synaptic integration of input from these diverse sources.

Pathophysiology of generalized photosensitive epilepsy in the cat.

Feline generalized penicillin-induced epilepsy is a reliable experimental model of epileptic photosensitivity. Binocular photic stimulation at 4-8 flashes/s consistently triggers generalized, bilaterally synchronous spike-and-wave discharges in cats submitted to long-term intramuscular penicillin administration at low dosage (50,000-150,000 IU/kg). The photically induced epileptic activity is first and mainly recorded from the cerebral cortex as compared with the lateral geniculate (GL) body, therefore supporting a cortical onset of epileptic photosensitivity. At this low penicillin dosage, only minimal spontaneous spike-and-wave activity is recorded. Bilateral GL stimulation is more effective than binocular photic stimulation in triggering spike-and-wave discharges, whereas unilateral GL stimulation is grossly ineffective. This observation implies a role of bilateral specific visual thalamocortical volleys in the genesis of epileptic photosensitivity. Five of 12 randomly selected cats receiving long-term penicillin exhibited spontaneous epileptic photosensitivity, a finding that suggests an underlying genetic predisposition of the feline species to this condition.

Effects of stimulation of the dorsocaudal claustrum on activities of striate cortex neurons in the cat

In the cat striate cortex, single electrical shocks applied to the dorsocausal claustrum (CLdc) elicited bimodal excitatory responses with about 12 and 26 ms latencies. About one-fourth of the cortical cells observed had CLdc-induced inhibitions with onset latencies longer than the excitations. On cortical field responses to geniculate stimulation, CLdc conditioning shocks exerted early facilitatory and late inhibitory effects which were shown to be not transmitted through the mesencephalic reticular formation.

Suppression of attack behavior in cats by stimulation of ventral tegmental area and nucleus accumbens

Low frequency (6 pps) stimulation of ventral tegmental area (VTA) and nucleus accumbens (NA) produced EEG synchronization and suppressed attack behavior elicited by hypothalamic stimulation. Both quiet biting and affective attack with rage were suppressed. Autonomic and non-directed somatic motor components of the attack reaction were unaffected. High frequency (60 pps) stimulation of VTA failed to suppress any components of the attack reaction; high frequency stimulation of NA, however, did produce suppression of attack. Low frequency (6 pps) sensory stimulation, delivered by photic or lateral geniculate stimulation, produced EEG synchronization but failed to cause suppression of attack. These results indicate that low frequency stimulation per se does not cause suppression of ongoing behavior. This study demonstrates that VTA and NA, components of the mesolimbic dopamine system, are involved in the inhibition of emotional-type behaviors.

Contradiction of auditory and visual information by brain stimulation.

Cats with permanently implanted electrodes were trained to discriminate between trains of flashes or clicks at two different repetition frequencies. After substantial overtraining with these sensory stimuli, high levels of stimulus generalization were obtained to electrical stimulation of the reticular formation at either frequency stimultaneously with contradictory flicker or click stimulation at the opposite frequency resulted in control of the behavior by the reticualr stimulus. Lateral geniculate stimulation failed to show this effect.

Recovery in visual cortical neurons following total visual deafferentation

Long-term effects of total visual deafferentation on the functional organization of the visual cortex were studied in freely behaving adult cats. Single unit activity in control records was compared with findings immediately after bilateral enucleation and after one month. Neuronal activity one month after enucleation was intermediate between control records and those immediately after enucleation, as revealed in the pattern and rate in maintained unit activity, unit responsiveness to geniculate stimulation, and in firing correlates of ponto-geniculo-occipital waves. The results suggest restoration of some basic cortical organizations in terms of neural excitability changes in shifting states of vigilance.

Excitability changes in various types of visual cortical units in freely behaving cats

Maintained and evoked unit activity was studied in the visual cortex of chronic cats. Recording conditions were differentiated into the 3 states by behavioral and electrical signs: resting arousal (RA), light sleep (LS) and deep sleep (DS or REM). The first and largest group (44.3%) increased neural excitability in the sequence LS → RA → DS. For the second (20.3%) and third group (11.4%) it was RA → LS → DS and DS → RA → LS, respectively. The first had a wide range of discharge rates (0.1–30.0/sec) and the third discharged extremely slowly (<0.1/sec in RA). These 3 main groups corresponded well to the 3 types of units classified on the basis of the correlation function between the mean discharge rate in RA and its changes in LS. Neural excitability was depressed in attentive arousal in comparison to RA. For some units (62.5%) there was noted a significant correlation between the mean discharge rate and the response latency to geniculate stimulation.

Immediate effects of total visual deafferentation on single unit activity in the visual cortex of freely behaving cats. I. Tonic excitability changes.

Effects of total visual deafferentation (eye enucleation) on maintained and evoked single unit activity in the cat visual cortex (VC) were studied. Three recording states were distinguished: resting arousal (RA), light sleep (LS) and deep sleep (DS). Two characteristic discharge patterns were noted in deafferented units. One was characterized by rhythmic synchronous firing of several units which was accompanied by high-amplitude slow wave bursts in the EEG (6–8/sec) during RA. Another was the abrupt occurrence of long-lasting spike trains which appeared unpredictively irrespective of vigilance levels. The overall discharge rate tended to decrease after deafferentation in both RA and DS while in LS tended to increase slightly. Three types of VC units were distinguished, as in intact ones, on the basis of the correlation function between the mean discharge rate in RA and its changes in LS. The relative incidence for the three types were different in the deafferented VC. The largest group (47.2%) had a sequence of mean discharge rate DS<RA<LS, while in intact animals the largest group (44.3%) had a sequence LS<RA<DS. For deafferented VC units the gradation of unit responsiveness to geniculate stimulation in the three states also paralleled that of the maintained discharge rate as in controls. A significant correlation between the mean discharge rate and the response latency to geniculate stimulation was not apparent following deafferentation due to loss of units with short latency responses and at the same time moderate discharge rates.

Influence of antidromic callosal volleys on single units in visual cortex

Thirteen to 30 days after unilateral visual cortex ablation or after ablation and complete transection of the corpus callosum, high-frequency callosal stimulation inhibited spontaneous and evoked unit activity in most cells sampled in the intact contralateral visual cortex. On the other hand, few units were excited by callosal stimulation. Since orthograde degeneration of callosal fibers should be complete by 11 days after the lesion, these effects are interpreted as resulting from antidromic activation of axon collaterals of callosal-projecting visual-cortex neurons. The antidromic inhibition was found to occlude orthodromic inhibition evoked by lateral geniculate stimulation and was often facilitated by a preceding brainstem reticular stimulation.

The interaction of visual attention and temporal cortex stimulation on electrical activity evoked in the striate cortex

Four experiments were directed at finding an index of the activity of the infero-temporal (IT) cortex on the visual system. In the first experiment, electrical stimulation of the IT cortex failed to alter recovery functions in the striate cortex of four monkeys. This result was different from that reported in an earlier experiment, but comparison of the initial recovery functions obtained in the two experiments allowed us to attribute the discrepancy to differences in the attentional state of the monkeys. This suggestion was tested by developing, in the second experiment, a reliable measure of state in the visual system, a measure responsive to environmental variables inducing attention. This measure was used in the third experiment to select and classify recovery cycles on the basis of the state of the visual system. Only when the attentive state was present were the recovery cycles similar to those recorded in the first experiment. Finally, the measure, a potential evoked in the striate cortex by geniculate stimulation, was shown to be sensitive to IT stimulation only when monkeys were in an inattentive state.

On the evoked mass-potential in relation to electrical background activity in the rabbit.

The relationships between the response configurations of evoked potentials and background EEG activities were investigated from the autocorrelogram and “response amplitude-frequency diagram” by using unanesthetized, immobilized rabbit.Autocorrelograms of EEGs in the arousal state during repetitive flas h stimulation showed an increase of regularity and decrease of noise elements in the amplitudes of the evoked potentials. This elevated brain activity level means the increased acuity and clarity of sensory informations.From the response amplitude-frequency diagram during repetitive lateral geniculate (GL) stimulation, the concentrating-accelerating tendency by arousal were evident in the activities of specific origin. That is to say, with change in the background EEG from sleep to arousal, every component of the cortical potentials evoked by GL stimulations of various frequencies were augmented and especially the responses to only one or two stimulating frequencies were found to show a concentrating increase. These frequencies correspond to the characteristic frequency in the specific system demonstrated in the previous paper (MIMURA et al., 1967). On the other hand, the responses to repetitive reticular (RF) stimulations of various low frequencies retained their irregularity in the response diagrams and, contrary to GL stimulation, their amplitudes were decreased due to arousal EEG. Peripherally induced responses to repetitive flash stimulation exhibited a very complicated behavior in their augmentative and depressive tendencies with change of background EEG, suggesting mixed or summated features due to both augmentative specific activities (by GL stimulation) and depressive non-specific activities (by RF stimulation).The spontaneous regular EEG wave in arousal was discussed from the resemblance of frequencies in relation to the activity changes of the evoked potential.

The central release of acetylcholine during consciousness and after brain lesions.

1. Acetylcholine (ACh) has been collected from the visual cortex of anaesthetized rabbits during stimulation of the lateral geniculate body and after cutting central nervous pathways. ACh has also been collected from the visual cortex of conscious, free-moving rabbits.2. After a unilateral ;vertical' lesion separating the geniculate body from more centrally situated nuclei, ACh release evoked from the contralateral cortex by geniculate body stimulation was abolished but evoked release from the ipsilateral cortex was only reduced.3. After a bilateral, ;horizontal' lesion separating the thalamic nuclei from the reticular formation, unilateral geniculate stimulation gave an increased ACh release from the ipsilateral but not from the contralateral visual cortex.4. The ;vertical' and ;horizontal' lesions had no permanent effect on the spontaneous release of ACh from the visual cortex.5. Unilateral destruction of the geniculate body reduced the spontaneous release of ACh from the ipsilateral cortex but did not affect the contralateral release.6. The spontaneous and directly evoked ACh release from chronically undercut areas of cortex was found to be considerably lower than from intact areas of cortex.7. A high output of ACh was obtained from the visual cortex of conscious, free-moving rabbits. The rate of ACh release was closely related to the activity and state of arousal of the animals.8. These results support an earlier suggestion that two major ascending cholinergic systems exist in the rabbit brain. One pathway is the non-specific reticulo-cortical tract responsible for cortical arousal and the other is the more specific thalamo-cortical pathway associated with augmenting and repetitive after-discharge responses. The functional significance of these two cholinergic pathways and their role in the conscious animal are discussed.

Effect of seizures in visual cortex on response to geniculate stimulation.

Electrical seizures elicited in the visual cortex of unanesthetized cats by direct cortical stimulation have been found to be associated with two phases of depression of the primary response evoked by single stimuli to the visual radiation fibers at their origin in the lateral geniculate body. Depression in the first phase, accompanying what has been called the after-discharge proper, was relatively small and probably in large measure the result of tetanization of the visual radiation fiber terminals. It is suggested, therefore, that the primary response and the after-discharge utilize different portions of the cortical circuitry. Depression in the later phase coincided with the appearance of grouped bursts of irregular spikes and slow waves, was of severe degree, and lasted several minutes. Depression of the radiation spike was prominent during this phase if the seizure was long. This phase has been identified with the spreading depression of previous investigators and was shown to depend, in part at least, upon the seizure itself and not simply upon the direct effects of the tetanic stimulating current.

Effect of interruption of the visual pathway on the response to geniculate stimulation.

Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.

IV. - Triple conducting pathway in the visual system and trichromatic vision

The pattern of the electrical response of the visual cortex to the stimulation of optic nerve or lateral geniculate body has been analyzed into three components representing the activity of three conducting pathways composed of three different sized fibers. The three components of the cortical response to geniculate stimulation can be selectively potentiated by continuous illumination of the retina with monochromatic lights. The red light enhances predominately the first component, green the second and blue the third. It is concluded that the nerve impulses for red are probably transmitted mainly by large sized fibers, those for green by medium and large sized fibers and those for blue by small fibers.