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PubMed2000

[The clinical value of click stimuli on the measurement of ipsilateral acoustic reflex thresholds].

OBJECTIVE: To define that click can substitute for pure tone as a stimulus to measure ipsilateral acoustic reflex thresholds, and to find out the effect of probe frequency on acoustic reflex thresholds. METHOD: Using middle ear analyzer (GSI 33, version 2), we measured 23 normal voluntary participants (46 ears) for getting the pure-tone generated ipsilateral acoustic reflex thresholds at different probe frequency and the click evoked ipsilateral acoustic reflex thresholds at click rate 100/s and 180/s for every ear. RESULT: For pure tone, the ipsilateral acoustic reflex thresholds at 500 Hz, 1000 Hz, 2000 Hz, were (84.35 +/- 6.96) dB, (84.65 +/- 5.93) dB, (87.96 +/- 6.36) dB by using 226 Hz probe; (93.13 +/- 6.54) dB, (92.70 +/- 6.33) dB, (93.35 +/- 5.99) dB by using 678 Hz probe; (86.52 +/- 4.72) dB, (87.48 +/- 5.00) dB, (88.30 +/- 6.16) dB by using 1000 Hz probe. For click, the ipsilateral acoustic reflex thresholds at click rate 100/s and 180/s were (89.78 +/- 6.83) dB, (92.07 +/- 7.42) dB by using 226 Hz probe; (90.44 +/- 6.76) dB, (90.65 +/- 6.38) dB by using 678 Hz probe; (88.04 +/- 6.87) dB, (88.69 +/- 7.42) dB by using 1000 Hz probe. The acoustic reflex thresholds for 678 Hz probe were higher than those obtained with 226 Hz and 1000 Hz probes. CONCLUSION: There were no artifact appearance while stimulus had been click at low rate, so click can be used for the measurement of ipsilateral acoustic reflex thresholds.

Acoustic Stimulation↗
PubMed1992

Contribution of polysynaptic pathways in the mediation and plasticity of Aplysia gill and siphon withdrawal reflex: evidence for differential modulation.

The gill and siphon withdrawal (GSW) reflex of Aplysia is centrally mediated by a monosynaptic and a polysynaptic pathway between sensory and motor neurons. The first objective of this article was to evaluate quantitatively the relative importance of these two components in the mediation of the GSW reflex. We have used an artificial sea water (ASW) solution containing a high concentration of divalent cations to raise the action potential threshold of the interneurons without affecting the monosynaptic component of the reflex (2:1 ASW). Compound EPSPs induced in gill or siphon motor neurons by direct stimulation of the siphon nerve or by tactile stimulation of the siphon skin were reduced by more than 75% in 2:1 ASW. These results indicate that interneurons intercalated between sensory and motor neurons are responsible for a considerable proportion of the afferent input to the motor neurons of the reflex. The second objective of this article was to compare the modulation of the monosynaptic and polysynaptic pathways. We have evaluated their respective contribution in sensitization of the GSW reflex by testing the effects of two neuromodulators of the reflex, 5-HT and small cardioactive peptide B (SCPB). We found that these two neuromodulators have a differential action on the two components of the GSW neuronal network. The polysynaptic pathway was more facilitated than the monosynaptic pathway by the neuropeptide SCPB. By contrast, 5-HT displayed an opposite selectivity. These results suggest that the polysynaptic component of the neuronal network underlying the GSW reflex is very important for its mediation. The data also indicate that the monosynaptic and polysynaptic components of the reflex can be differentially modulated. The diversity of modulatory actions at various sites of the GSW network should be relevant for learning-associated modifications in the intact animal.

Action Potentials↗
PubMed1992

[Jaw opening reflex: a new electrophysiologic method for objective assessment of trigeminal sensory disorders. I. Method and normal values].

Retrospective analysis of trigeminal nerve evoked potentials in 40 consecutive patients, most of them with traumatic nerve lesions, showed that in 12 cases no trigeminal nerve SEP were obtainable, and 11 of the remaining 28 patients had normal trigeminal nerve SEP. Therefore the jaw-opening reflex was investigated as a potential tool for electrophysiologic analysis of facial sensory disturbances. The jaw-opening reflex was investigated in 60 healthy subjects (31 female, 29 male) aged 23-82 years. It was elicited by electrical 0.1 ms square wave pulses delivered to the lower and upper lips and to the infraorbital region on either side at a rate below 1 per 5s. The EMG responses were recorded from the bilateral masseter and temporalis muscles at a moderate voluntary activation. Under these conditions, the jaw-opening reflex reveals itself as two inhibitory pauses of the ongoing EMG on both sides, the onset latency of the first EMG-suppression being 10-15 ms, and of the second 35-50 ms. Particular attention was paid to the stimulus strength at threshold (TR) to evoke the jaw-opening reflex. We found that the jaw-opening reflex was constantly evoked by weak stimuli applied to the 2nd and 3rd trigeminal branches. Bilateral reflex responses with unilateral stimulation were a regular finding. The reflex responses increase with increasing stimulus strength (Fig. 1). Moderate to forcible activation of the jaw closing muscles is a prerequisite for optimum recordings of the jaw-opening reflex (Fig. 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Reduction of clinical temporomandibular joint pain is associated with a reduction of the jaw-stretch reflex.

AIMS: To examine the jaw-stretch reflex after injection of local anesthetic (LA) into painful temporomandibular joints (TMJs), since the functional role of jaw-stretch reflexes in patients with painful temporomandibular disorders is still not well understood. METHODS: Thirteen female patients with a clinical diagnosis of disc displacement without reduction and TMJ pain participated in this open study. Reflex responses were evoked by fast stretches at 15% of the maximal voluntary contraction level before and after injection of 1 mL carbocaine into the painful TMJ. Electromyographic (EMG) activity was recorded from the left and right masseter and temporalis muscles, and the mean level of prestimulus EMG activity and peak-to-peak amplitude of the stretch reflex were measured. Visual analog scale ratings of TMJ pain and TMJ pressure pain thresholds (PPTs) were also obtained. Eleven healthy women were examined with the same protocol (except for PPT determinations) before and after injection of LA into the TMJ. RESULTS: In patients, injection of LA reduced the TMJ pain during jaw movements and maximum clenching (P < .021) and increased the PPTs in the painful TMJ (P < .01). The prestimulus EMG activity in the masseter on the painful side (feedback muscle) was unaffected by the injection of LA (P > .262). There were no significant side-to-side asymmetries of latency or amplitude measures of the stretch reflex in the patient group. Both the peak-to-peak amplitude and the normalized peak-to-peak amplitude of the stretch reflex were reduced in the masseter and temporalis muscles on the painful side and in the masseter on the nonpainful side after LA injections (P < .048). There were no effects of LA injections into the TMJ in the healthy group on any EMG or stretch parameters. CONCLUSION: These results do not support the notion of asymmetries in the jaw-stretch reflex in patients with TMJ pain, but they do suggest that the reflex sensitivity can be influenced by nociceptive activity from the TMJ area.

Adult↗
PubMed2006

Frequency rhythmic electrical modulation system (FREMS) on H-reflex amplitudes in healthy subjects.

AIM: Changes in the amplitude of Hoffmann reflex (H-reflex) may reflect variations in the characteristics of the largely monosynaptic circuitry that is explored and are a possible target for diagnostic and physical therapeutic intervention. However, previous attempts to induce predictable changes in the H-reflex amplitude by transcutaneous electrical nervous stimulation (TENS) have generally failed. Previous workers applied fixed frequency in the low- (2-5 Hz) or in the high- (100 Hz) field, but they did not attempt to vary frequency and/or impulse duration in time. METHODS: We evaluated the effect of a new type of painless electric stimulation, i.e. frequency rhythmic electrical modulation system (FREMS). FREMS is characterized by the use of transcutaneous electric pulses with sequentially modulated frequency (f: 1-39 Hz) and width (w: 10-40 micro s) at constant, perceptive threshold voltage (approximately 150 V). FREMS was applied at the abductor hallucis muscle (AHM), as conditioning stimulus of the H-reflex which was recorded ipsilaterally at the soleus muscle, according to the classic method, in 10 normal volunteers (age range 21-40 years). RESULTS: H-reflex amplitude was substantially decreased (-50%) during FREMS and H-reflex amplitude variations were influenced by w/f variation in time during FREMS subphase C in a predictable way (r(2)=0.43; P<0.001). Our results suggest an effective ability of FREMS to modulate H reflex amplitude. CONCLUSIONS: The ability to achieve large and predictable changes of the H-reflex amplitude simply by modulating both frequency and duration of a conditioning painless electrical stimulation offers new possibilities for the treatment of diseases characterized by motoneuron excitability abnormalities.

Action Potentials↗
PubMed1991

Sympathetic reflex control of blood flow in human peripheral tissues.

Sympathetic vasoconstrictor reflexes are essential for the maintenance of arterial blood pressure in upright position. It has been generally believed that supraspinal sympathetic vasoconstrictor reflexes elicited by changes in baroreceptor activity play an important role. Recent studies on human skeletal muscle, cutaneous and subcutaneous tissues of the limbs indicate that the situation is more complex. Measurements have been carried out during acute as well as chronic sympathetic denervation. Spinal sympathetic reflex mechanisms have been evaluated in tetraplegic patients, where supraspinal sympathetic vasoconstrictor reflexes are blocked. Blood flow has been measure by the local 133Xe-technique. The results indicate the presence of spinal as well as supraspinal sympathetic vasoconstrictor reflexes to human peripheral tissues. Especially is emphasized the presence of a local sympathetic veno-arteriolar axon reflex which is elicited by increase in venous transmural pressure of more than about 25 mm Hg. Finally, centrally elicited vasoconstrictor activity is modified by simultaneously activating the local veno-arteriolar axon reflex or vice versa by means of an intraneuronal impulse inhibition due to collision of normodromically and antidromically conducted impulses in efferent sympathetic vasoconstrictor fibers. The evidence obtained suggests that sympathetic vasoconstrictor reflexes to postural changes are complex and highly differentiated.

Blood Pressure↗
PubMed1991

Fusimotor reflexes influencing secondary muscle spindle afferents from flexor and extensor muscles in the hind limb of the cat.

The purpose of this study was to investigate secondary muscle spindle afferents from the triceps-plantaris (GS) and posterior biceps and semitendinosus (PBSt) muscles with respect to their fusimotor reflex control from different types of peripheral nerves and receptors. The activity of single secondary muscle spindle afferents was recorded from dissected and cut dorsal root filaments in alpha-chloralose anaesthetized cats. Both single spindle afferents and sets of simultaneously recorded units (2-3) were investigated. The modulation and mean rate of firing of the afferent response to sinusoidal stretching of the GS and PBSts muscle were determined. Control measurements were performed in the absence of any reflex stimulation, while test measurements were made during reflex stimulation. The reflex stimuli consisted of manually performed movements of the contralateral hind limb, muscle stretches, ligament tractions and electrical stimulations of cutaneous afferents. Altogether 21 secondary spindle afferents were investigated and 20 different reflex stimuli were employed. The general responsiveness (i.e. number of significant reflex effects/number of control-test series) was 52.4%, but a considerable variation between different stimuli was found, with the highest (89.9%) for contralateral whole limb extension and the lowest (25.0%) for stretch of the contralateral GS muscle. The size of the response to a given stimulus varied considerably between different afferents, and, in the same afferent, different reflex stimuli produced effects of varying size. Most responses were characterized by an increase in mean rate of discharge combined with a decrease in modulation, indicative of static fusimotor drive (Cussons et al., 1977). Since the secondary muscle spindle afferents are part of a positive feedback loop, projecting back to both static and dynamic fusimotor neurones (Appelberg Et al., 1892 a, 1983 b; Appelberg et al., 1986), it is suggested that the activity in the loop may work like an amplified which, during some circumstances, enhance the effect of other reflex inputs to the system (Johansson et al., 1991 b).

Afferent Pathways↗
PubMed1977

[Measurement of muscle reflex time in radicular disorders of the lumbosacral region].

The results of studies performed by the authors show that time measurements of proprioceptive muscular reflexes (triceps surae and tibialis posterior reflexes) may be considered a valuable addition to methods of topical diagnosis of radicular disturbances in the lumbosacral region. The reflexes were tested in twenty normal subjects. There were found an intraindividual constancy of the respective reflex time with a maximum deviation of 2 ms as well as a lateral variability up to 1.3 ms. Radicular compressions resulted in an increase in reflex time by 2 to 66 ms or failure of the reflex potential to be recorded. The pathological cases were compared with clinical and neurological studies, positive myelographies using radiopaque substances, and results of surgical operations. Compared with the results of surgical operations, changes in reflex time indicated damage to the reflex arc in ninety percent of the cases.

Humans↗
PubMed1990

Respiratory modulation of the cutaneous somatosympathetic reflex in normotensive (WKY) and in spontaneously hypertensive rats (SHR): species and strain-dependent patterns.

In 6 normotensive Wistar-Kyoto (WKY) and 6 spontaneously hypertensive rats (SHRs) anesthetized with urethane and chloralose, paralyzed, artificially ventilated, vagotomized with carotid sinus nerves bilaterally cut, somatosympathetic reflex discharges were recorded in cervical and renal nerves by stimulating group II and III cutaneous afferents in the sural nerve. Only a long-circuited, late supraspinal component reflex discharge could be elicited. After averaging the responses evoked by random stimulation, the latency of the reflex discharge was significantly longer in the renal than in the cervical sympathetic nerve, equally in the WKY rat and in SHR. In WKY rats the peak of sympathetic discharge corresponded to early expiration, whereas in SHRs--to late inspiratory phase. The duration of the reflex discharge elicited in inspiration was greater in SHR than in WKY rats. In WKY rats stimuli applied during phrenic discharge produced a reflex response of longer latency and of reduced amplitude than those applied in expiration. In SHRs the latency of the reflex response in the sympathetic cervical nerve was shorter during inspiration than in expiratory phase. The timing of the sympathetic reflex responsiveness within respiratory cycle in SHR and in WKY rats corresponded to strain-dependent opposite respiratory synchronization pattern of the spontaneous sympathetic activity characterizing each strain. No respiratory modulation of the somatosympathetic reflex was observed in the renal nerve of SHR. It is concluded that both spontaneous and evoked sympathetic activity is synchronized differently in SHR and in WKY rats and this difference is both species- and strain-dependent.

Animals↗
PubMed1990

[Examination of the rectosphincteric reflex by means of endoscopic electrical stimulation. A new device].

An endoscopic electrical stimulation method (the new method) for the examination of the rectosphincteric reflex was devised to overcome difficulties attributable to the manometric method using balloon stimulation. Safety of the electrical stimulation under the conditions used routinely, was confirmed symptomatically and histologically. It was found that the optimal parameters of electrical stimulation to obtain the recto-sphincteric reflex were: 1 ms, 20 Hz, 5 to 7mA, and for 3 sec. The degree of the reflex relaxation became less and the time lag of the response to the stimulation became longer, as the distance of the stimulation site from the anal verge was increased. These relationships were significant. In the cases which received anterior resection of the rectum, the rectosphincteric reflex was examined using the new method. In 12 of 39 cases the recto-sphincteric reflex was induced by stimulation at the oral side of the anastomosis. In all of them the reflex was observed at 9 or more months postoperatively. Incidence of postoperative reflex appearance tended to be higher after end-to-end anastomosis than after side-to-end anastomosis. In two cases which received Duhamel-Okamoto's operation and in one which received Soave-Denda's operation, it was possible to analyze the relationship between the stimulating site and presence or absence of the reflex-like phenomenon.

Adult↗
PubMed1989

Effect of acute or chronic administration of imipramine on spinal and supraspinal micturition reflexes in rats.

Acute imipramine administration (15 mg/kg i.p. 60 min before) increased the threshold for activating the spinal but not the supraspinal vesico-vesical micturition reflex in urethane-anesthetized rats. On the other hand, "chronic" imipramine administration (15 mg/kg i.p./day for 5 consecutive days) increased selectively the threshold of the supraspinal micturition reflex. Intravenous administration of cumulative doses of imipramine (up to 14 mg/kg) exerted a progressive inhibitory effect on the supraspinal reflex and voiding efficiency, possibly related to direct inhibition of muscular contractility at the bladder level. However, with the dose regimen used to compare the action of imipramine on spinal and supraspinal reflexes (15 mg/kg i.p., 60 min before), imipramine did not affect the volume-pressure curve or myogenic activity in decentralized bladders (bilateral removal of pelvic ganglia). The effect of acute imipramine on threshold of the spinal vesico-vesical reflex was absent in rats receiving oral p-chlorophenylalanine to deplete 5-hydroxytryptamine stores in the central nervous system. On the other hand, p-chlorophenylalanine pretreatment did not prevent the action of chronic imipramine administration on the supraspinal reflex. Acute administration of desipramine, the major metabolite of imipramine, increased threshold of the spinal but not supraspinal micturition reflex. These findings indicate that the ability of imipramine to modulate vesico-urethral motility at the central nervous system level may involve different mechanisms. Inhibition of 5-hydroxytryptamine reuptake in nerve terminals may be important for the acute modulatory effect of imipramine on the spinal reflex.

Animals↗
PubMed1989

[The effect of stimulation of the substantia nigra on low- and high-threshold startle reflexes in the cat].

Effects of the substantia nigra (pars compacta) stimulation on two functional types of startle reflexes were studied in chloralose-anesthetized cats. The reflexes were the low-threshold ones evoked by tactile stimuli (T-reflex) and high-threshold ones evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS reflex). It was found that substantia nigra stimulation exerted mainly inhibitory influences on both types of reflexes. However the depression of the SBS-reflex was always more profound and long lasting (up to 8 min) than that of T-reflex. The latter reflex was sometimes facilitated.

Animals↗
PubMed1989

[Comparative study on the reflex responses of carotid and aortic baroreceptors in the rabbit].

In 81 anesthetized rabbits, the baroreflex control of heart rate (HR), hind-limb vascular resistance (HVR) and renal sympathetic nerve activity (RSNA) was observed during arterial baroreceptor loading and unloading by intravenously injecting phenylephrine (PE) and nitroprusside (NP). The results were as follows: (1) An increase of arterial pressure with PE caused reduction in HR, HVR and RSNA, while a decrease of arterial pressure with NP evoked opposite responses. These reflex responses were reproducible. (2) By either carotid baroreceptor denervation (CBRX) or aortic baroreceptor denervation (ABRX), the reflex changes of HR induced by injecting PE and NP were impaired (P less than 0.01), while the reflex responses in HVP remained unchanged. Despite of the enhanced basal RSNA following ABRX or CBRX, the magnitude of reflex inhibition in RSNA during injecting NP was similar to that before denervation, whereas that of the reflex excitation in RSNA during injecting NP was reduced (P less than 0.05). (3) After complete sino-aortic denervation (SAD), the change of arterial pressure following PE or NP injection was enhanced, but the reflex changes in HR, HVR and RSNA were significantly diminished (P less than 0.001). (4) Vagotomy abolished the residual reflex changes observed after SAD. The results indicate that the aortic and carotid baroreceptors may regulate HR in a simple additive manner, while the aortic baroreceptor seems to be more important. Furthermore, both the aortic and carotid baroreceptors may play important roles for the reflex control of HVR and RSNA, and operate mutually by the way of inhibitory summation.

Animals↗
PubMed1989

[Does a "transcortical" loop of the long-latency muscle reflex exist?].

EMG responses were produced by electric stimulation of the dermal branches of the nn. digilates of the index finger of the right hand and recorded from the m. interosseus dorsalis I. during its slight isometric contraction. The mean initial latency of a long-latency muscular reflex was 50.68 ms in men and 49.13 in women. The author mentions some arguments indicating the probable existence of a transcortical loop: The latency of long-latency reflexes increases gradually from proximal to distal muscles. The short-latency component of the somatosensory evoked potential N20 appears mid-time between the time of the stimulus and the onset of the long-latency reflex and thus the time interval in the long-latency reflex is sufficient for a transcortical loop. The author found a facilitation of the muscular reflex response as well as of the preparatory cortical potential during the preparatory period of voluntary flexion of the fingers during concurrent electric stimulation of the peripheral nerve. The late reflex component increases considerably and is better synchronized during the movement of the thumb instead of isometric contraction, because during kinetic innervation afferent impulses reach the precentral cortex at a higher facilitated level. These results document well the modifiable, plastic behaviour of transcortical reflexes. The method of long-latency reflexes can be used in electrophysiological diagnosis of disorders of the CNS and it is promising also in therapeutic stimulation rehabilitation and in locomotor reeducation.

Adult↗
PubMed1989

[Influence of stimulation of the central gray matter on low- and high-threshold startle reflexes].

Influences of the periaqueductal gray matter (PAG) stimulation on high-threshold jaw opening reflex (JOR) evoked by tooth pulp stimulation and on two functional types of startle reflexes were studied in chloralose anesthetized cats; the startle reflexes were high-threshold ones evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS, reflex) and low-threshold ones evoked by tactile stimuli (tactile spino-reticulo-spinal, TSRS, reflex). Stimulation of the majority of PAG sites induced considerable inhibition of JOR as well as profound depression of SBS-reflexes and moderate depression of TSRS-reflexes. Some PAG sites were found to exert a facilitatory action on the latter reflex. Effects of PAG stimulation were short-term (hundred ms) and/or long-lasting (minutes). Possible mechanisms of these effects are discussed.

Animals↗
PubMed1985

Suppression of reflex tachycardia by central administration of the alpha-1 adrenoceptor antagonists urapidil and prazosin in anesthetized dogs.

The present study was designed to determine if central administration of the alpha-1 adrenoceptor antagonists urapidil and prazosin would suppress baroreceptor-induced reflex tachycardia elicited by bradykinin and bilateral carotid occlusion in pentobarbital-anesthetized dogs. Urapidil and prazosin were infused intracisternally in doses ranging from 25 to 200 and 1 to 4 micrograms/kg, respectively. Urapidil suppressed reflex tachycardia elicited by bradykinin with little or no reduction in the pressor response to i.v. phenylephrine in vagotomized dogs or those with vagi intact. When reflex tachycardia was elicited by bilateral carotid occlusion urapidil suppressed the tachycardic response only when the vagi were intact. Prazosin also suppressed bradykinin-induced reflex tachycardia, but to a lesser degree than urapidil. Doses of prazosin that reduced reflex tachycardia also decreased the pressor response to i.v. phenylephrine. In order to authenticate that suppression of reflex tachycardia by urapidil was due to a central effect, urapidil was injected i.v. in doses shown previously to be effective intracisternally. When given i.v., urapidil failed to inhibit bradykinin-induced tachycardia, thus verifying a central site of action. No doses of urapidil or prazosin infused centrally affected basal blood pressure or heart rate. These data indicate that urapidil and prazosin, when administered intracisternally, suppress reflex tachycardia and that urapidil may be more effective than prazosin at this central site. Suppression of bradykinin-induced reflex tachycardia by urapidil and prazosin may be due to blockade of central alpha adrenoceptors, which are involved in the increased sympathetic outflow evoked by baroreceptor inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1986

[Negative inotropic reflex effects in the dog ventricle before and after beta-receptor blockade].

Myocardial contractility of the rabbit ventricle, expressed as contractility index KI = d log (p - p0)/dtmax, was altered by both aortic nerve reflex stimulation and by beta-receptor blockade with propranolol (Obsidan) and talinolol (Cordanum, (+)-Cordanum and (-)-Cordanum). In every case, beta-receptor blockade decreased negative reflex inotropy, whereas reflex hypotension was only reduced by Obsidan. The mean reflex inotropy was 11.8% after Obsidan application and 17.3% after Cordanum injection, the reflex hypotension 28.0% and 34.8%. From the results it is concluded that Cordanum acts in the rabbit ventricle cardioselectively. If neural and pharmacological effects are related to initial effects, we may conclude that the contractile state maintained by the resting sympathetic tone is diminished. The overall reduction of KI by Cordanum blockade and reflex inhibition amounts to 45.5%, that of blood pressure to 42%. Its optical isomers act also cardioselectively, the inotropic effects, however, are smaller than those of the racemate. Obviously, reflex stimulation and beta 1-blocking agents have a similar mode of inotropic action. From this we suggest that reflex inotropy is mediated by sympathetic nerve fibres and beta 1-adrenergic receptors.

Adrenergic beta-Antagonists↗
PubMed1988

The orienting ocular-following reflex in pretrigeminal cats with lesions of visual and oculomotor systems.

The brain stem was transected in cats at the pretrigeminal level. Additional lesions were placed in 17 cats, whereas 10 served as controls without further manipulation. All received a small dose of amphetamine. The vertical following reflex was evoked by a slit of light or a black bar (1degrees X 4degrees). The stimuli moved along the vertical 'meridian or parall to it up to 40 degrees in the left or right hemifield. A unilateral removal of the superior colliculus produced a loss of reflexes evoked from the contralateral hemifield. In contrast, after unilateral ablation of the visual cortex only in one of 4 cats was the reflex from the contralateral hemifield smaller than ipsilaterally; and after unilateral ablation of the frontal oculomotor cortex, no hemifield asymmetry of these reflexes was found in any cat. The reflexes also survived bilateral ablation of the visual cortex or the frontal oculomotor cortex. After transection of the corpus callosum the reflexes were virtually normal. The data confirm that in the cat the orienting fixation reflex is mediated by the superior colliculus. On the other hand, this reflex appears to be largely independent of the cerebral cortex.

Animals↗