Bimodal Stimulation Research Articles

Integration of visual and auditory information in bimodal neurones in the guinea-pig superior colliculus.

We have investigated the responses of neurones in the guinea-pig superior colliculus to combinations of visual and auditory stimuli. When these stimuli were presented separately, some of these neurones responded only to one modality, others to both and a few neurones reliably to neither. To bimodal stimulation, many of these neurones exhibited some form of cross-modality interaction, the degree and nature of which depended on the relative timing and location of the two stimuli. Facilitatory and inhibitory interactions were observed and, occasionally, both effects were found in the same neurone at different inter-stimulus intervals. Neurones whose responses to visual stimuli were enhanced by an auditory stimulus were found in the superficial layers. Although visual-enhanced and visual-depressed auditory neurones were found throughout the deep layers, the majority of them were recorded in the stratum griseum profundum. Neurones that responded to both visual and auditory stimuli presented separately and gave enhanced or depressed responses to bimodal stimulation were found throughout the deep layers, but were concentrated in the stratum griseum intermediale and extended into the stratum opticum.

Integration of visual and infrared information in bimodal neurons in the rattlesnake optic tectum.

Bimodal neurons in the rattlesnake tectum, which receive sensory input from the retina and from the infrared-sensing pit organ, exhibit novel, highly nonlinear cross-modality interactions. Some units respond only to simultaneous bimodal stimulation. Others respond to only one of the two modalities, but show greatly enhanced or depressed responses when stimulated simultaneously in the second modality. These cross-modality interactions may play an important role in recognizing and orienting toward biologically important objects.

Visual-vestibular convergence in the vestibular nuclei of the cat

Responses from neurons of the vestibular nuclei were recorded in N2O-anaesthetized cats. Most neurons in the rostral parts of the nuclei responded to bimodal visual-vestibular stimulation, following a trapezoidal velocity profile. Both combinations of the two stimuli were tested: rotation of the animal with stationary visual field and rotation with overtaking visual field, i.e. the visual pattern running in the same direction as the turntable with twice the velocity. Some correlation of physiological data with results in corresponding psychophysical experiments were found. As a possible biological function of visual-vestibular convergence a phylogenetic solution for discrimination of body and outer world movement is discussed.

The role of cutaneous mechanoreceptors in thermal sensation and pain

The functional behavior of slowly adapting cutaneous mechanoreceptors under combined thermal—mechanical stimulation was investigated by singleunit recordings from the lumbar dorsal roots of the cat. Increased sensitivity to bimodal stimulation was observed in 24 of the 28 units studied, employing stimulus—response functional behavior as the basis for judgment. Low-threshold receptors generally did not exhibit increased spontaneous firing as accompaniment to heightened sensitivity, while such enhanced basal activity was usually observed in moderate-threshold units in addition to increased reactivity. Information theory calculations performed on these stimulus—response data revealed that 15 of the 24 ‘heat-sensitive’ receptors were additionally characterized by an enhanced ability to transmit neural information under bimodal stimulation. These results were interpreted as supporting pattern theories of pain as opposed to the concept of receptor specificity. No contradiction was observed, however, between the present results and those of other investigators. The present conclusions derive from new criteria for thermal reactivity based upon innovative stimulus conditions.

Habituation of postsynaptic unit responses of the cat motor cortex to stimuli of different modalities

Habituation (extinction) of postsynaptic unit responses of the cat motor cortex to repetitive electrodermal, photic, acoustic, and combined bimodal stimulation was investigated by intracellular recording. Habituation was shown by a decrease in the number of spikes per grouped discharge and a decrease in the amplitude and duration of the EPSPs, and sometimes IPSPs, on repetition of the stimulus. The way in which the course of habituation depends on the modality and duration of stimulation (at a constant frequency of 1/sec) is examined. Habituation of postsynaptic responses to sensory stimuli is observed with neurons of different functional groups, namely identified neurons of pyramidal tract and unidentified neurons, some of which were evidently pyramidal neurons and interneurons. The hypothesis is put forward that the habituation of PSPs of the cortical neurons is based on processes taking place mainly at the subcortical level.

Effect of Mycobacterium phlei upon reticuloendothelial system of mice of different ages.

A single intravenous injection of Mycobacterium phlei Halpern into mice (1 to 12 months old) elicited a bimodal stimulation of global phagocytic activity. The liver and spleen became enlarged, but returned to normal size after about 2 months. A simple formula was developed for rating the efficiency of the phagocytic organs of mice by taking into account the hepatosplenomegaly accompanying RES stimulation.

BIMODAL STIMULATION OF THE RETICULOENDOTHELIAL SYSTEM BY MYCOBACTERIUM PHLEI

A variety of substances which stimulate the reticuloendothelial system (RES) in the mouse were rated in potency by employing active dry bakers' yeast as the reference stimulant. Mycobacterium phlei Halpern was found to be a particularly effective RES stimulant. A single intravenous injection of this microorganism elicited a bimodal stimulation of global phagocytic activity. The peak rates of phagocytosis occurred at 1 and 21 days post administration. M. phlei Halpern also caused pronounced hypertrophy of the liver and spleen. Six weeks elapsed before these organs returned to normal size.

BIMODAL STIMULATION OF THE RETICULOENDOTHELIAL SYSTEM BY MYCOBACTERIUM PHLEI

A variety of substances which stimulate the reticuloendothelial system (RES) in the mouse were rated in potency by employing active dry bakers' yeast as the reference stimulant. Mycobacterium phlei Halpern was found to be a particularly effective RES stimulant. A single intravenous injection of this microorganism elicited a bimodal stimulation of global phagocytic activity. The peak rates of phagocytosis occurred at 1 and 21 days post administration. M. phlei Halpern also caused pronounced hypertrophy of the liver and spleen. Six weeks elapsed before these organs returned to normal size.