Sensitivity of Auditory Cortical Neurons to the Locations of Leading and Lagging Sounds

2005 ◽  
Vol 94 (2) ◽  
pp. 979-989 ◽  
Author(s):  
Brian J. Mickey ◽  
John C. Middlebrooks
Keyword(s):  
Unit Activity ◽  
Cortical Neurons ◽  
Precedence Effect ◽  
Related Information ◽  
Sound Levels ◽  
Transmission Of Information ◽  
Discrete Responses ◽  
Temporal Firing ◽  
Spike Patterns ◽  
Awake Cats

We recorded unit activity in the auditory cortex (fields A1, A2, and PAF) of anesthetized cats while presenting paired clicks with variable locations and interstimulus delays (ISDs). In human listeners, such sounds elicit the precedence effect, in which localization of the lagging sound is impaired at ISDs ≲10 ms. In the present study, neurons typically responded to the leading stimulus with a brief burst of spikes, followed by suppression lasting 100–200 ms. At an ISD of 20 ms, at which listeners report a distinct lagging sound, only 12% of units showed discrete lagging responses. Long-lasting suppression was found in all sampled cortical fields, for all leading and lagging locations, and at all sound levels. Recordings from awake cats confirmed this long-lasting suppression in the absence of anesthesia, although recovery from suppression was faster in the awake state. Despite the lack of discrete lagging responses at delays of 1–20 ms, the spike patterns of 40% of units varied systematically with ISD, suggesting that many neurons represent lagging sounds implicitly in their temporal firing patterns rather than explicitly in discrete responses. We estimated the amount of location-related information transmitted by spike patterns at delays of 1–16 ms under conditions in which we varied only the leading location or only the lagging location. Consistent with human psychophysical results, transmission of information about the leading location was high at all ISDs. Unlike listeners, however, transmission of information about the lagging location remained low, even at ISDs of 12–16 ms.

Responses of Auditory Cortical Neurons to Pairs of Sounds: Correlates of Fusion and Localization

2001 ◽  
Vol 86 (3) ◽  
pp. 1333-1350 ◽  
Author(s):  
Brian J. Mickey ◽  
John C. Middlebrooks
Keyword(s):  
Cortical Neurons ◽  
Stimulus Level ◽  
Precedence Effect ◽  
Localization Dominance ◽  
Fused Image ◽  
Single Burst ◽  
Left And Right ◽  
The Difference ◽  
Spike Patterns ◽  
Intense Source

When two brief sounds arrive at a listener's ears nearly simultaneously from different directions, localization of the sounds is described by “the precedence effect.” At inter-stimulus delays (ISDs) <5 ms, listeners typically report hearing not two sounds but a single fused sound. The reported location of the fused image depends on the ISD. At ISDs of 1–4 ms, listeners point near the leading source (localization dominance). As the ISD is decreased from 0.8 to 0 ms, the fused image shifts toward a location midway between the two sources (summing localization). When an inter-stimulus level difference (ISLD) is imposed, judgements shift toward the more intense source. Spatial hearing, including the precedence effect, is thought to depend on the auditory cortex. Therefore we tested the hypothesis that the activity of cortical neurons signals the perceived location of fused pairs of sounds. We recorded the unit responses of cortical neurons in areas A1 and A2 of anesthetized cats. Single broadband clicks were presented from various frontal locations. Paired clicks were presented with various ISDs and ISLDs from two loudspeakers located 50° to the left and right of midline. Units typically responded to single clicks or paired clicks with a single burst of spikes. Artificial neural networks were trained to recognize the spike patterns elicited by single clicks from various locations. The trained networks were then used to identify the locations signaled by unit responses to paired clicks. At ISDs of 1–4 ms, unit responses typically signaled locations near that of the leading source in agreement with localization dominance. Nonetheless the responses generally exhibited a substantial undershoot; this finding, too, accorded with psychophysical measurements. As the ISD was decreased from ∼0.4 to 0 ms, network estimates typically shifted from the leading location toward the midline in agreement with summing localization. Furthermore a superposed ISLD shifted network estimates toward the more intense source, reaching an asymptote at an ISLD of 15–20 dB. To allow quantitative comparison of our physiological findings to psychophysical results, we performed human psychophysical experiments and made acoustical measurements from the ears of cats and humans. After accounting for the difference in head size between cats and humans, the responses of cortical units usually agreed with the responses of human listeners, although a sizable minority of units defied psychophysical expectations.

Cortical Representation of Auditory Space: Information-Bearing Features of Spike Patterns

2002 ◽  
Vol 87 (4) ◽  
pp. 1749-1762 ◽  
Author(s):  
Shigeto Furukawa ◽  
John C. Middlebrooks
Keyword(s):  
Sound Source ◽  
Neuronal Response ◽  
Source Location ◽  
Spike Timing ◽  
Spike Count ◽  
Cortical Representation ◽  
Auditory Space ◽  
Transmitted Information ◽  
Related Information ◽  
Spike Patterns

Previous studies have demonstrated that the spike patterns of cortical neurons vary systematically as a function of sound-source location such that the response of a single neuron can signal the location of a sound source throughout 360° of azimuth. The present study examined specific features of spike patterns that might transmit information related to sound-source location. Analysis was based on responses of well-isolated single units recorded from cortical area A2 in α-chloralose-anesthetized cats. Stimuli were 80-ms noise bursts presented from loudspeakers in the horizontal plane; source azimuths ranged through 360° in 20° steps. Spike patterns were averaged across samples of eight trials. A competitive artificial neural network (ANN) identified sound-source locations by recognizing spike patterns; the ANN was trained using the learning vector quantization learning rule. The information about stimulus location that was transmitted by spike patterns was computed from joint stimulus-response probability matrices. Spike patterns were manipulated in various ways to isolate particular features. Full-spike patterns, which contained all spike-count information and spike timing with 100-μs precision, transmitted the most stimulus-related information. Transmitted information was sensitive to disruption of spike timing on a scale of more than ∼4 ms and was reduced by an average of ∼35% when spike-timing information was obliterated entirely. In a condition in which all but the first spike in each pattern were eliminated, transmitted information decreased by an average of only ∼11%. In many cases, that condition showed essentially no loss of transmitted information. Three unidimensional features were extracted from spike patterns. Of those features, spike latency transmitted ∼60% more information than that transmitted either by spike count or by a measure of latency dispersion. Information transmission by spike patterns recorded on single trials was substantially reduced compared with the information transmitted by averages of eight trials. In a comparison of averaged and nonaveraged responses, however, the information transmitted by latencies was reduced by only ∼29%, whereas information transmitted by spike counts was reduced by 79%. Spike counts clearly are sensitive to sound-source location and could transmit information about sound-source locations. Nevertheless, the present results demonstrate that the timing of the first poststimulus spike carries a substantial amount, probably the majority, of the location-related information present in spike patterns. The results indicate that any complete model of the cortical representation of auditory space must incorporate the temporal characteristics of neuronal response patterns.

Evidence for a supplementary eye field

1987 ◽  
Vol 57 (1) ◽  
pp. 179-200 ◽  
Author(s):  
J. Schlag ◽  
M. Schlag-Rey
Keyword(s):  
Unit Activity ◽  
Cortical Neurons ◽  
Cortical Area ◽  
Head Movements ◽  
Frontal Eye Field ◽  
Unit Recording ◽  
Electrical Microstimulation ◽  
Preferred Direction ◽  
Supplementary Eye Field ◽  
Eye Field

Electrical microstimulation and unit recording were performed in dorsomedial frontal cortex of four alert monkeys to identify an oculomotor area whose existence had been postulated rostral to the supplementary motor area. Contraversive saccades were evoked from 129 sites by stimulation. Threshold currents were lower than 20 microA in half the tests. Response latencies were usually longer than 50 ms (minimum: 30 ms). Eye movements were occasionally accompanied by blinks, ear, or neck movements. The cortical area yielding these movements was at the superior edge of the frontal lobe just rostral to the region from which limb movements could be elicited. Depending on the site of stimulation, saccades varied between two extremes: from having rather uniform direction and size, to converging toward a goal defined in space. The transition between these extremes was gradual with no evidence that these two types were fundamentally different. From surface to depth of cortex, direction and amplitude of evoked saccades were similar or changed progressively. No clear systematization was found depending on location along rostrocaudal or mediolateral axes of the cortex. The dorsomedial oculomotor area mapped was approximately 7 mm long and 6 mm wide. Combined eye and head movements were elicited from one of ten sites stimulated when the head was unrestrained. In the other nine cases, saccades were not accompanied by head rotation, even when higher currents or longer stimulus trains were applied. Presaccadic unit activity was recorded from 62 cells. Each of these cells had a preferred direction that corresponded to the direction of the movement evoked by local microstimulation. Presaccadic activity occurred with self-initiated as well as visually triggered saccades. It often led self-initiated saccades by more than 300 ms. Recordings made with the head free showed that the firing could not be interpreted as due to attempted head movements. Many dorsomedial cortical neurons responded to photic stimuli, either phasically or tonically. Sustained responses (activation or inhibition) were observed during target fixation. Twenty-one presaccadic units showed tonic changes of activity with fixation. Justification is given for considering the cortical area studied as a supplementary eye field. It shares many common properties with the arcuate frontal eye field. Differences noted in this study include: longer latency of response to electrical stimulation, possibility to evoke saccades converging apparently toward a goal, and long-lead unit activity with spontaneous saccades.

scholarly journals Rat primary auditory cortex is tuned exclusively to the contralateral hemifield

2013 ◽  
Vol 110 (9) ◽  
pp. 2140-2151 ◽  
Author(s):  
Justin D. Yao ◽  
Peter Bremen ◽  
John C. Middlebrooks
Keyword(s):  
Auditory Cortex ◽  
Sound Source ◽  
Cortical Neurons ◽  
Free Field ◽  
Primary Auditory Cortex ◽  
Homogeneous Population ◽  
Spatial Sensitivity ◽  
Spatial Tuning ◽  
Sound Levels

The rat is a widely used species for study of the auditory system. Psychophysical results from rats have shown an inability to discriminate sound source locations within a lateral hemifield, despite showing fairly sharp near-midline acuity. We tested the hypothesis that those characteristics of the rat's sound localization psychophysics are evident in the characteristics of spatial sensitivity of its cortical neurons. In addition, we sought quantitative descriptions of in vivo spatial sensitivity of cortical neurons that would support development of an in vitro experimental model to study cortical mechanisms of spatial hearing. We assessed the spatial sensitivity of single- and multiple-neuron responses in the primary auditory cortex (A1) of urethane-anesthetized rats. Free-field noise bursts were varied throughout 360° of azimuth in the horizontal plane at sound levels from 10 to 40 dB above neural thresholds. All neurons encountered in A1 displayed contralateral-hemifield spatial tuning in that they responded strongly to contralateral sound source locations, their responses cut off sharply for locations near the frontal midline, and they showed weak or no responses to ipsilateral sources. Spatial tuning was quite stable across a 30-dB range of sound levels. Consistent with rat psychophysical results, a linear discriminator analysis of spike counts exhibited high spatial acuity for near-midline sounds and poor discrimination for off-midline locations. Hemifield spatial tuning is the most common pattern across all mammals tested previously. The homogeneous population of neurons in rat area A1 will make an excellent system for study of the mechanisms underlying that pattern.

scholarly journals Neuronal adaptation reveals a suboptimal decoding of orientation tuned populations in the mouse visual cortex

2018 ◽  
Author(s):  
Miaomiao Jin ◽  
Jeffrey M. Beck ◽  
Lindsey L. Glickfeld
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Cortical Neurons ◽  
Signal To Noise Ratio ◽  
Sensory Information ◽  
Orientation Discrimination ◽  
Signal To Noise ◽  
Neuronal Adaptation ◽  
Related Information ◽  
Mouse Visual Cortex

AbstractSensory information is encoded by populations of cortical neurons. Yet, it is unknown how this information is used for even simple perceptual choices such as discriminating orientation. To determine the computation underlying this perceptual choice, we took advantage of the robust adaptation in the mouse visual system. We find that adaptation increases animals’ thresholds for orientation discrimination. This was unexpected since optimal computations that take advantage of all available sensory information predict that the shift in tuning and increase in signal-to-noise ratio in the adapted condition should improve discrimination. Instead, we find that the effects of adaptation on behavior can be explained by the appropriate reliance of the perceptual choice circuits on target preferring neurons, but the failure to discount neurons that prefer the distractor. This suggests that to solve this task the circuit has adopted a suboptimal strategy that discards important task-related information to implement a feed-forward visual computation.

scholarly journals State-dependent cortical unit activity reflects dynamic brain state transitions in anesthesia

2020 ◽  
Author(s):  
Heonsoo Lee ◽  
Shiyong Wang ◽  
Anthony G. Hudetz
Keyword(s):  
Unit Activity ◽  
Spike Timing ◽  
Transfer Entropy ◽  
Brain State ◽  
Electromyographic Activity ◽  
Cortical Unit ◽  
Timing Variability ◽  
Brain States ◽  
Spike Patterns ◽  
Dose Dependent

ABSTRACTHow anesthesia affects cortical neuronal spiking and information transfer could help understand the neuronal basis of conscious state. Recent investigations suggest that global state of the anesthetized brain is not stationary but changes spontaneously at a fixed level of anesthetic concentration. How cortical unit activity changes with dynamically transitioning brain states under anesthesia is unclear. We hypothesized that distinct cortical states are characterized by distinct neuronal spike patterns. Extracellular unit activity was measured with sixty-four-channel silicon microelectrode arrays in cortical layers 5/6 of primary visual cortex of chronically instrumented, freely moving male rats (N = 7) during stepwise reduction of the anesthetic desflurane (6, 4, 2, and 0%). Unsupervised machine learning applied to multi-unit spike patterns revealed five distinct brain states of which four occurred at various anesthetic concentrations and shifted spontaneously. In deeper anesthesia states, the number of active units and overall spike rate decreased while the remaining active units showed increased bursting (excitatory neurons), spike timing variability, unit-to-population correlation and unit-to-unit transfer entropy, especially among putative excitatory units, despite the overall decrease in transfer entropy. A novel desynchronized brain state with increased spike timing variability, entropy and electromyographic activity that occurred mostly in deep anesthesia was discovered. These results provide evidence for distinct unit activity patterns associated with spontaneous changes in local cortical brain states at stationary anesthetic conditions. The appearance of a paradoxical, desynchronized brain state in deep anesthesia contends the prevailing view of monotonic dose-dependent anesthetic effects on the brain.SIGNIFICANCE STATEMENTRecent studies suggest that spontaneous changes in brain state occur under anesthesia. However, the spiking behavior of cortical neurons associated with such state changes has not been investigated. We found that local brain states defined by multi-unit activity had non-unitary relationship with the current anesthetic level. A paradoxical brain state displaying asynchronous firing pattern and high electromyographic activity was found unexpectedly at high-dose anesthesia. In contrast, the synchronous fragmentation of neuronal spiking appeared to be a robust signature of the state of anesthesia. The findings challenge the assumption of monotonic, anesthetic dose-dependent behavior of cortical neuron populations. They enhance the interpretation of neuroscientific data obtained under anesthesia and understanding of the neuronal basis of anesthetic-induced state of unconsciousness.

Serotonin (5-HT2) receptor mediated enhancement of cortical unit activity

1992 ◽  
Vol 70 (12) ◽  
pp. 1604-1609 ◽  
Author(s):  
R. S. Neuman ◽  
G. Zebrowska
Keyword(s):  
Unit Activity ◽  
Cortical Neurons ◽  
Cortical Excitability ◽  
Noxious Stimulation ◽  
Pial Surface ◽  
Neocortical Neurons ◽  
Cortical Unit ◽  
Iontophoretic Application ◽  
Anaesthetized Rats

Simultaneous single-unit and intracortical activity were recorded from neocortical neurons in urethane-anaesthetized rats to investigate the role of serotonin (5-HT) in modifying cortical excitability. Units, at a depth of 775–1100 μm from the pial surface, discharged in a burst–pause pattern that was correlated with slow wave activity. Application of noxious somatic stimulation resulted in cortical desynchronization and altered the pattern of unit activity such that firing was continuous, i.e., the pauses were eliminated. Intravenous administration of the mixed 5-HT1C/5-HT2 antagonists (cinanserin, cyproheptadine, ketanserin, and ritanserin) prevented both desynchronization and the change in unit activity induced by noxious stimulation within 2.5–15 min of the injection. The basic pattern of burst–pause activity remained intact, but the number of spikes per burst was typically reduced, whereas interburst intervals were increased. Iontophoretic application of these antagonists onto cortical neurons resulted in actions similar to those observed following systemic administration. Intravenous and iontophoretic application of m-trifluomethylphenylpiperazine (5-HT1C agonist, 5-HT2 antagonist) resulted in actions indistinguishable from those observed with the above antagonists, from which we conclude 5-HT2 and not 5-HT1C receptors mediate the alteration in unit activity observed with noxious stimulation. The results are discussed with respect to an interaction between N-methyl-D-aspartate and 5-HT2 receptors leading to the enhanced unit activity observed with noxious stimulation.Key words: neocortex, serotonin antagonists, unit activity, noxious stimulation, desynchronization.

Activity and excitability to electrical current of cortical auditory receptive neurons of awake cats as affected by stimulus association

1976 ◽  
Vol 39 (5) ◽  
pp. 1045-1061 ◽  
Author(s):  
C. D. Woody ◽  
J. D. Knispel ◽  
T. J. Crow ◽  
P. A. Black-Cleworth
Keyword(s):  
Auditory Stimulus ◽  
Conditioned Reflex ◽  
Unit Activity ◽  
Temporal Order ◽  
Electrical Current ◽  
Spike Discharge ◽  
Suprasylvian Cortex ◽  
Evoked Activity ◽  
Awake Cats

1. Unit activity and excitability were studied at the midlateral and suprasylvian cortex of naive, blink-conditioned and "randomization" cats. The latter received the same CS and US as did the conditioned animals, but in random temporal order and with random intertrial intervals with mean comparable to that used for conditioning. The randomization group failed to develop a blink CR. 2. With conditioning, spontaneous and evoked unit discharges were increased above levels found in naive animals. Correspondingly, levels of extracellularly injected current required to elicit a spike discharge were lower in conditioned than in naive animals. In addition, in the conditioned animals, the degree of enhancement of evoked activity and excitability was found to be greatest in the units that responded to the CS, as opposed to units that responded to another auditory stimulus of equal intensity but of no special behavioral significance vis-a-vis the conditioned reflex. 3...

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