PubMed · 6676149
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G A Tavartkiladze. Auditory brainstem evoked potentials.. https://pubmed.ncbi.nlm.nih.gov/6676149/
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A nuclear magnetic resonance imaging (MRI) method is presented for quantitatively mapping the physical response of a material to harmonic mechanical excitation. The resulting images allow calculation of regional mechanical properties. Measurements of shear modulus obtained with the MRI technique in gel materials correlate with independent measurements of static shear modulus. The results indicate that displacement patterns corresponding to cyclic displacements smaller than 200 nanometers can be measured. The findings suggest the feasibility of a medical imaging technique for delineating elasticity and other mechanical properties of tissue.
Nitric oxide (NO) is a short-lived radical species endowed with intercellular signalling functions in the mammalian brain. In the present study we have investigated the effects of focal injection into one inferior colliculus of N omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, on the acoustic middle latency responses (MLRs) evoked by click stimuli and recorded from the auditory cortex in anaesthetized rats. Microinfusion of L-NAME (1.0 mM) did not alter the latency of MLRs nor did it affect the evoked brain stem responses (ABRs). By contrast, L-NAME reduced P1a-N1 amplitude of MLRs by 51.7 +/- 6.6% (mean +/- SEM; n = 5) and almost complete recovery to background amplitude was obtained 15-25 min after treatment. The less active isomer, D-NAME (1.0 mM; n = 5), failed to produce consistent effects on the evoked MLRs. A higher concentration of L-NAME (5.0 mM; n = 5) yielded a 69.0 +/- 13.3% inhibition whereas maximum inhibition produced by 0.5 mM (n = 3) L-NAME was approximately equal to 10% of control value. The inhibitory effect typically evoked by 1.0 mM L-NAME was prevented by treating rats with L-arginine (5.0 mM; n = 5), the endogenous precursor of NO synthesis. Reduction of MLR amplitude was also obtained in rats receiving intracollicular injection of dizocilpine (MK801; 1.0 microM) and LY274614 (1.0 mM), two selective N-methyl-D-aspartate (NMDA) receptor antagonists. In conclusion, the present data support a role for intracollicular NO in the processing and transmission of the acoustic input to the auditory cortex in the rat.
We studied the effects of collision between a voluntary command and the startle response by interrupting a simple visual reaction time task with an acoustic startle. We observed two main effects. First, the reaction time was markedly shortened when the startle was delivered at intervals of 0-75 ms after the 'go' signal. Second, the startle response elicited when the subject's attention was focused onto reacting to the visual 'go' signal involved more muscles and induced larger EMG responses than when the startling stimulus was delivered unexpectedly. Startle response and voluntary commands may share a number of structures along the motor path. Reaction time can be shortened up to the latency of a startle response if the voluntary command is issued a short time after the startling stimulus. Facilitation of the startle responses during motor preparation may be due to the excitability enhancement that occurs in various neural structures along the motor path before the onset of EMG activity.