Journal of Neurophysiology

Carlile, S.; King, A. J.

doi: N/Apmid: 8176440

Abstract 1. The role of the structures of the outer ear in producing monaural and binaural spectral cues to sound location was examined acoustically in the ferret. A probe microphone was introduced across the wall of the external auditory canal and its responses to digitally constructed wideband signals were recorded for a large number of free field locations. 2. In the intact animal the patterns of both monaural and binaural cues were asymmetrical for horizontal locations about the interaural axis. For anterior sound locations the monaural transformations demonstrated relative gains at middle and high frequencies and a location-dependent frequency notch. Changing elevation resulted in variations in the corner frequencies of these spectral features. Additionally, there was greater front-back asymmetry in the binaural spectral cues for locations in lateral space when compared with locations near the midline. 3. Surgical removal of the pinna and concha (pinnectomy) eliminated all the major front-back asymmetrical features in the horizon monaural and binaural spectral transformations as well as the elevation-dependent variations in the monaural spectra. Thus the residual transformations were ambiguous for sound locations in lateral space, resulting in "cones of confusion" centered on the interaural axis. 4. These cues were reflected in the topographic representation of auditory space in the deeper layers of the superior colliculus (SC). Previous studies have shown that spatial tuning at near-threshold sound levels is based on monaural pinna cues, whereas binaural inputs are utilized at higher levels that stimulate both ears. In the intact ferret we examined statistically the topography of the representation of sound azimuth for near-threshold and suprathreshold stimuli and the alignment of the auditory and visual representations in the SC. The distributions of auditory best positions within the SC for near- and suprathreshold stimulus levels were statistically indistinguishable, suggesting that both monaural and binaural cues are integrated in this neural representation of space. 5. Pinnectomy resulted in a large increase in the number of auditory units that responded best to two distinct locations in space. One lobe of the response was tuned appropriately in terms of the position of the unit within the SC, demonstrating that the residual acoustical cues are sufficient for the construction of a topographic representation of auditory space. However, the second region of space, thereby producing an ambiguous representation.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Swadlow, H. A.

doi: N/Apmid: 8176419

Abstract 1. Properties of antidromically identified efferent neurons within the cortical representation of the vibrissae, sinus hairs, and philtrum were examined in motor cortex of fully awake adult rabbits. Efferent neurons were tested for both receptive field and axonal properties and included callosal (CC) neurons (n = 31), ipsilateral corticocortical (C-IC) neurons (n = 34) that project to primary somatosensory cortex (S-1), and corticofugal neurons of layer 5 (CF-5) (n = 33) and layer 6 (CF-6) (n = 32) that project to and/or beyond the thalamus. Appropriate collision tests demonstrated that substantial numbers of corticocortical efferent neurons project an axon to both the corpus callosum and to ipsilateral S-1. 2. Suspected interneurons (SINs, n = 37) were also studied. These neurons were not activated antidromically from any stimulus site but did respond synaptically to electrical stimulation of the ventrolateral (VL) thalamus and/or S-1 with a burst of three or more spikes at frequencies from 600 to > 900 Hz. All of these neurons also responded synaptically to stimulation of the corpus callosum. The action potentials of these neurons were much shorter in duration (mean = 0.48 ms), than those of efferent neurons (mean = 0.90 ms). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 4.1 spikes/s, CC, C-IC, and CF-6 neurons all had mean values of < 1 spike/s. Axonal conduction velocities of CF-5 neurons were much higher (mean = 12.76 m/s) than either CC (1.47 m/s), C-IC (0.97 m/s), or CF-6 (mean = 1.96 m/s) neurons. A decrease in antidromic latency (the "supernormal" period) followed a single prior impulse in most CC, C-IC, and CF-6 neurons but was minimal or absent in CF-5 neurons. Although all but two CF-5 neurons responded to peripheral sensory stimulation, many CC (35%), C-IC (59%), or CF-6 (66%) neurons did not. CC, CF-5, and CF-6 neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. 4. Sensory receptive fields of neurons in motor cortex were considerably larger than those observed in S-1 but were similar in size to those seen in secondary somatosensory cortex (S-2).(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Celichowski, J.; Emonet-Denand, F.; Laporte, Y.; Petit, J.

doi: N/Apmid: 8176434

Abstract 1. The intrafusal muscle fiber(s) activated in cat peroneus tertius spindles by single static gamma (gamma s) axons were identified by exclusively physiological criteria based on the different contractile properties of chain and bag2 fibers. 2. The identification rested both on the features of primary ending discharges observed during gamma s electrical stimulation at a rate of 30 pulses per second (stimulation at 30/s) and on cross-correlograms constructed during stimulation at 100/s. Three types of primary ending activation could be distinguished. 3. Type F (fast) activations are characterized, at 30/s, by either a 1-to-1 driving or a very irregular increase in firing arising from a level close to the frequency of stimulation and by the presence in cross-correlograms of significant peaks. They are ascribed to chain fibers whose contractions, at 30/s, present large oscillations and, at 100/s, are still incompletely fused. 4. Type S (slow) activations are characterized, at 30/s, by a sustained and generally regular increase in firing and by the absence of significant peaks in cross-correlograms constructed during stimulation at 100/s. They are ascribed to bag2 fibers whose contractions are nearly fused at 30/s and completely fused beyond 60-70/s. 5. Type M (mixed) activations are characterized, at 30/s, by an irregular increase of discharge above a level distinctly higher than the frequency of stimulation and by the presence of significant peaks in cross-correlograms. They are ascribed to the coactivation of chain and bag2 fibers for two reasons: first, they have some features of both type F and type S activations; and second, they are readily reproduced by stimulating together two axons supplying the same spindle, one exerting a type F activation, the other a type S activation. 6. In seven experiments the distribution of 42 single gamma s axons was determined by observing the type of activation they exerted on several spindles (from 3 to 6). Thirty-five axons (83%) were classified "nonspecific" because the type of activation (F, S, or M) varied from one spindle to the other. Seven axons (17%) were classified "specific" because the type of activation was the same in all spindles: either type F for five axons (12%) or type S for two axons (5%). A statistical analysis of the distribution of all activations showed that the proportions of specific axons were not significantly different from those predicted by chance. Copyright © 1994 the American Physiological Society

Flanders, M.; Pellegrini, J. J.; Soechting, J. F.

doi: N/Apmid: 8176443

Abstract 1. Temporal patterns of electromyographic (EMG) activity were related to the direction of fast reaching movements. Reaches were to 20 targets in the sagittal plane of the human arm. 2. The subtraction of EMG levels recorded during very slow movements to each target allowed this study to focus on the phasic aspects of complex EMGs. 3. General features of the phasic spatial/temporal patterns differed across muscles, even across muscles at the same joint. This indicates that future models of cortical to motoneuronal processing must include nonuniform space-time transformations. Copyright © 1994 the American Physiological Society

Aizawa, H.; Tanji, J.

doi: N/Apmid: 8176424

Abstract 1. We studied the responsiveness of neurons in the primary motor cortex (MI) of monkeys (Macacafuscata) to electrical stimulation of the supplementary motor area (SMA), primary sensory cortex (SI), and the ventral subnucleus of the thalamus (VPLo) with chronically implanted electrodes. 2. All neurons examined in this study were characterized by their relation to a motor task performed by the animals. They responded to stimulation of the cortical or thalamic area with excitation from one area alone (n = 128) or from multiple areas (n = 84) of all combinations. In a majority of neurons, response latencies to both cortical and thalamic stimulation were within 5 ms. 3. A vast majority of neurons (80%) that were active during a preparatory period for forthcoming reaching movements were activated by SMA stimulation. They were activated only infrequently by SI or thalamic stimulation. 4. Movement-related neurons (active immediately before and during reaching movements) were activated by thalamic, SI, or SMA stimulation or by any combination of those stimuli. More than half of the movement-related neurons activated exclusively by either thalamic or SMA stimulation exhibited activity onset times earlier than those observed in the earliest muscles. By contrast, most movement-related neurons that responded only to SI stimulation were late in their activity onset. 5. These findings suggest that the SMA input to MI is important in developing a preparatory type of activity in MI, whereas the thalamus (VPLo) provides substantial inputs in movement execution. The roles played by inputs from SI and SMA in relation to motor execution are debatable and are discussed here with reference to previous reports. Copyright © 1994 the American Physiological Society

Condon, C. J.; White, K. R.; Feng, A. S.

doi: N/Apmid: 8176439

Abstract 1. Neurophysiological recordings were undertaken to determine how neurons in the central nucleus of the inferior colliculus (ICc) of the little brown bat, Myotis lucifugus, extract amplitude modulations that span across a series of tone pulses (i.e., signals that simulate echoes from fluttering targets). Two types of stimuli were presented to the bats. The first served as a control and consisted of an unmodulated train of tone pulses having different repetition rates (TPu, 5-400 pulses per second). The second was a train of tone pulses that were sinusoidally amplitude modulated (TPm, 5-110 Hz) across sequential pulses. The modulated trains of pulses were presented at five different repetition rates (25, 50, 100, 200, and 400 pulses per second) encompassing the range of biosonar emission rates in these bats at different stages of target-directed flight. 2. One hundred fifty-two single neurons were isolated in the ICc of M. lucifugus; their basic response properties and temporal firing patterns were characterized. The best frequencies (BFs) ranged from 10 to 80 kHz and the minimum thresholds at BF were distributed widely (10-95 dB SPL). The frequency tuning selectivity ranged widely, from very broadly tuned (Q10dB = 1.3) to narrowly tuned (Q10dB = 89). Units with very narrow frequency tuning (Q values > 20) were restricted to BFs of 30-50 kHz. The temporal firing pattern of ICc units could be categorized into primary-like (PL), chopper (C), onset-immediate (OI), and onset-late (OL). 3. In response to TPu ICc units exhibited varying degrees of response selectivities as evidenced by their count-based response functions (using the spike count as a measure) versus repetition rate. The count-based response functions of ICc units exhibited five filtering characteristics including band-pass, low-pass, high-pass, band-suppression, and all-pass characteristics. The temporal firing pattern of a unit showed certain correlations with its count-based response function. For example, the majority of OI and OL units, and about half of the C units, showed tuned band-pass response functions. The remaining C and onset types showed mostly low-pass response functions. In contrast, PL neurons showed mostly high-pass response functions, but one third displayed band-pass response functions. 4. The ability of ICc neurons to time-lock their discharges to the individual pulses in a train was characterized by using the synchronization coefficient (SC) as a measure. The SC was plotted against the repetition rate to construct units' synchronization-based response function.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Yagi, T.; Macleish, P. R.

doi: N/Apmid: 7513752

Abstract 1. The membrane properties of cone inner segments dissociated enzymatically from monkey retina were studied under voltage-clamp conditions using patch pipettes in the whole-cell clamp configuration. 2. A noninactivating, voltage-gated calcium current was evoked at potentials positive to -60 mV and peaked between -30 and -20 mV when barium was substituted for calcium. Cadmium (50 microM) but not nickel (50 microM) blocked the current. 3. A large calcium-activated anion current (IAn) was observed when the membrane potential was set to a level between -60 and 30 mV. The reversal potential of IAn was 0 mV with chloride as the sole anion and about -30 and -40 mV when methanesulfonate and D-aspartate, respectively, replaced intracellular chloride to set the equilibrium potential for chloride at -50 mV. IAn inactivated and oscillated when the membrane potential was maintained at depolarized levels, contrary to calcium-activated anionic currents seen in photoreceptors of other species. 4. A sustained-type potassium current was activated by depolarizations positive to -50 mV. The time course of activation and deactivation were voltage dependent. This potassium current was partially blocked by 20 mM tetraethylammonium ions. 5. A transient potassium current was activated by depolarizations positive to -20 mV. This current was blocked by 4-aminopyridine (2 mM) and inactivated with a time constant of approximately 500 ms. The amplitude in response to voltage steps to 45 mV was decreased by prepulses to voltages more positive than -30 mV. 6. Hyperpolarization negative to -65 mV activated an inward current that was completely blocked by external cesium (10 mM). The reversal potential suggested a conductance mechanism permeable to both sodium and potassium ions. 7. A calcium-activated potassium current, which was found in salamander photoreceptors, was not detected. 8. The presence of these conductances is expected to influence the membrane potential and the time course of the light response in monkey cones. Copyright © 1994 the American Physiological Society

Schnabolk, C.; Raphan, T.

doi: N/Apmid: 8176431

Abstract 1. A considerable amount of attention has been devoted to understanding the velocity-position transformation that takes place in the control of eye movements in three dimensions. Much of the work has focused on the idea that rotations in three dimensions do not commute and that a "multiplicative quaternion model" of velocity-position integration is necessary to explain eye movements in three dimensions. Our study has indicated that this approach is not consistent with the physiology of the types of signals necessary to rotate the eyes. 2. We developed a three-dimensional dynamical system model for movement of the eye within its surrounding orbital tissue. The main point of the model is that the eye muscles generate torque to rotate the eye. When the eye reaches an orientation such that the restoring torque of the orbital tissue counterbalances the torque applied by the muscles, a unique equilibrium point is reached. The trajectory of the eye to reach equilibrium may follow any path, depending on the starting eye orientation and eye velocity. However, according to Euler's theorem, the equilibrium reached is equivalent to a rotation about a fixed axis through some angle from a primary orientation. This represents the shortest path that the eye could take from the primary orientation in reaching equilibrium. Consequently, it is also the shortest path for returning the eye to the primary orientation. Thus the restoring torque developed by the tissue surrounding the eye was approximated as proportional to the product of this angle and a unit vector along this axis. The relationship between orientation and restoring torque gives a unique torque-orientation relationship. 3. Once the appropriate torque-orientation relationship for eye rotation is established the velocity-position integrator can be modeled as a dynamical system that is a direct extension of the one-dimensional velocity-position integrator. The linear combination of the integrator state and a direct pathway signal is converted to a torque signal that activates the muscles to rotate the eyes. Therefore the output of the integrator is related to a torque signal that positions the eyes. It is not an eye orientation signal. The applied torque signal drives the eye to an equilibrium orientation such that the restoring torque equals the applied torque but in the opposite direction. The eye orientation reached at equilibrium is determined by the unique torque-orientation relation. Because torque signals are vectors, they commute.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Okada, Y.; Teeter, J. H.; Restrepo, D.

doi: N/Apmid: 8176428

Abstract 1. The effect of intracellular application of inositol 1,4,5-trisphosphate (IP3) from the patch pipette was analyzed in isolated rat olfactory neurons under whole-cell patch clamp. 2. Intracellular dialysis of 10 microM 1,4,5-IP3 in K(+)-internal solution induced a sustained depolarization of 35.8 +/- 10.5 (SD) mV (n = 16). The IP3-induced response was observed in 75% of the cells dialyzed with IP3 but not when 10 microM ruthenium red was also included in the pipette solution (4 cells). Lower concentrations (50-100 nM) of 2,4,5-IP3 induced similar responses to those produced by 1,4,5-IP3 in five of eight olfactory neurons. 3. Steady-state I-V relationships of IP3-gated currents with K(+)-internal solution were classified into two types: outwardly rectifying and N-shaped. In Cs(+)-internal solution outwardly rectifying and linear patterns were observed. 4. The IP3-induced currents were inhibited by external Cd2+ (1 mM). The reversal potentials of the Cd(2+)-inhibitable currents were -16.1 mV (n = 2) and -29.0 +/- 7.1 mV (n = 3) for the outwardly rectifying and N-shaped types, respectively, in K(+)-internal solution. The reversal potential was -5.9 +/- 6.8 mV (n = 5) in the Cs(+)-internal solution. 6. In contrast, the Ca(2+)-ionophore, ionomycin (5 microM) hyperpolarized the olfactory neurons and greatly potentiated the outward currents at positive holding membrane potential. 7. The data suggest that IP3 can depolarize rat olfactory neurons without mediation by intracellular Ca2+. Copyright © 1994 the American Physiological Society

Pickar, J. G.; Hill, J. M.; Kaufman, M. P.

doi: N/Apmid: 8176437

Abstract 1. In decerebrate cats, we investigated the responses of group III muscle afferents to dynamic exercise. The cats performed low intensity dynamic exercise on a treadmill. Group III afferent activity from the dynamically exercising triceps surae muscles was recorded from L7-S1 dorsal root filaments. 2. Single-unit recordings were obtained from 15 group III afferent fibers whose receptive fields were in the triceps surae muscles and from one group III afferent whose receptive field was in the flexor digitorum longus muscle. Conduction velocities for the 16 group III afferents ranged from 3.0 to 27.9 m/s (15.6 +/- 1.9 m/s, mean +/- SE). 3. Ten of 16 group III muscle afferents were stimulated by dynamic exercise. Of the 10, 7 were strongly responsive and 3 were mildly responsive to dynamic exercise. Each of the 10 afferents displayed at least some activity that was synchronized to the contraction phase of the step cycle. The mean developed tensions for strongly responsive afferents, mildly responsive afferents, and afferents that did not respond were 0.8 +/- 0.3, 1.3 +/- 0.5, and 0.7 +/- 0.3 Kg, respectively (P > 0.05). Thus differences in the responsiveness of the afferents to exercise were not attributable to differences in developed tensions. 4. The group III afferents that were strongly responsive to dynamic exercise were also mechanically sensitive. Each strongly responsive afferent (n = 7) was stimulated by nonnoxious pressure applied to its receptive field. Most strongly responsive afferents (n = 5) were stimulated by stretch of the triceps surae muscles.(ABSTRACT TRUNCATED AT 250 WORDS) Copyright © 1994 the American Physiological Society