Azimuthal sensitivity of neurons in primary auditory cortex of cats. II. Organization along frequency-band strips

1990 ◽  
Vol 64 (3) ◽  
pp. 888-902 ◽  
Author(s):  
R. Rajan ◽  
L. M. Aitkin ◽  
D. R. Irvine
Keyword(s):  
Spatial Distribution ◽  
Auditory Cortex ◽  
Frequency Band ◽  
Primary Auditory Cortex ◽  
Companion Paper ◽  
Significant Feature ◽  
Central Field ◽  
Cortical Surface ◽  
Peak Response ◽  
The Individual

1. The organization of azimuthal sensitivity of units across the dorsoventral extent of primary auditory cortex (AI) was studied in electrode penetrations made along frequency-band strips of AI. Azimuthal sensitivity for each unit was represented by a mean azimuth function (MF) calculated from all azimuth functions obtained to characteristic frequency (CF) stimuli at intensities 20 dB or more greater than threshold. MFs were classified as contrafield, ipsi-field, central-field, omnidirectional, or multipeaked, according to the criteria established in the companion paper (Rajan et al. 1990). 2. The spatial distribution of three types of MFs was not random across frequency-band strips: for contra-field, ipsi-field, and central-field MFs there was a significant tendency for clustering of functions of the same type in sequentially encountered units. Occasionally, repeated clusters of a particular MF type could be found along a frequency-band strip. In contrast, the spatial distribution of omnidirectional MFs along frequency-band strips appeared to be random. 3. Apart from the clustering of MF types, there were also regions along a frequency-band strip in which there were rapid changes in the type of MF encountered in units isolated over short distances. Most often such changes took the form of irregular, rapid juxtapositions of MF types. Less frequently such changes appeared to show more systematic changes from one type of MF to another type. In contrast to these changes in azimuthal sensitivity seen in electrode penetrations oblique to the cortical surface, much less change in azimuthal sensitivity was seen in the form of azimuthal sensitivity displayed by successively isolated units in penetrations made normal to the cortical surface. 4. To determine whether some significant feature or features of azimuthal sensitivity shifted in a more continuous and/or systematic manner along frequency-band strips, azimuthal sensitivity was quantified in terms of the peak-response azimuth (PRA) of the MFs of successive units and of the azimuthal range over which the peaks occurred in the individual azimuth functions contributing to each MF (the peak-response range). In different experiments shifts in these measures of the peaks in successively isolated units along a frequency-band strip were found generally to fall into one of four categories: 1) shifts across the entire frontal hemifield; 2) clustering in the contralateral quadrant; 3) clustering in the ipsilateral quadrant; and 4) clustering about the midline. In two cases more than one of these four patterns were found along a frequency-band strip.(ABSTRACT TRUNCATED AT 400 WORDS)

Representation of cochlea within primary auditory cortex in the cat

1975 ◽  
Vol 38 (2) ◽  
pp. 231-249 ◽  
Author(s):  
M. M. Merzenich ◽  
P. L. Knight ◽  
G. L. Roth
Keyword(s):  
Auditory Cortex ◽  
Frequency Band ◽  
Constant Width ◽  
Primary Auditory Cortex ◽  
Cortical Surface ◽  
Cortical Layers ◽  
Secondary Field ◽  
Mapping Techniques ◽  
Cochlear Partition ◽  
Tonal Stimuli

The representation of sound frequency (and of the cochlear partition) within primary auditory cortex has been investigated with use of microelectrode-mapping techniques in a series of 25 anesthetized cats. Among the results were the following: 1) Within vertical penetrations into AI, best frequency and remarkably constant for successively studied neurons across the active middle and deep cortical layers. 2) There is an orderly representation of frequency (and of represented cochlear place) within AI. Frequency is rerepresented across the mediolateral dimension of the field. On an axis perpendicular to this plane of rerepresentation, best-frequency (represented cochlear place) changes as a simple function of cortical location. 3) Any given frequency band (or sector of the cochlear partition) is represented across a belt of cortex of nearly constant width that runs on a nearly straight axis across AI. 4) There is a disproportionately large cortical surface representation of the highest-frequency octaves (basal cochlea) within AI. 5) The primary and secondary field locations were somewhat variable, when referenced to cortical surface landmarks. 6) Data from long penetrations passing down the rostral bank of the posterior ectosylvian sulcus were consistent with the existence of a vertical unit of organization in AI, akin to cortical columns described in primary visual and somatosensory cortex. 7) Responses to tonal stimuli were encountered in fields dorsocaudal, caudal, ventral, and rostral to AI. There is an orderly representation of the cochlea within the field rostal to AI, with a reversal in best frequencies across its border with AI. 8) Physiological definitions of AI boundaries are consistent with their cytoarchitectonic definition. Some of the implications of these findings are discussed.

Azimuthal sensitivity of neurons in primary auditory cortex of cats. I. Types of sensitivity and the effects of variations in stimulus parameters

1990 ◽  
Vol 64 (3) ◽  
pp. 872-887 ◽  
Author(s):  
R. Rajan ◽  
L. M. Aitkin ◽  
D. R. Irvine ◽  
J. McKay
Keyword(s):  
Auditory Cortex ◽  
Stimulus Intensity ◽  
Primary Auditory Cortex ◽  
Companion Paper ◽  
Broadband Noise ◽  
Central Field ◽  
Sound Sources ◽  
Common Effect ◽  
Response Range ◽  
Definition Of

1. Preliminary to studying the organization of azimuthal sensitivity of neurons along frequency-band strips in the primary auditory cortex (AI) of cat (see companion paper), this study examined the sensitivity of 251 units in cat AI to variations in the azimuthal location of sound sources in the frontal hemifield. Most units (231) were tested with tones at the characteristic frequency (CF; frequency to which the unit had the lowest threshold). Unit CFs ranged from 5 to 36 kHz. A large number of units (91) were tested with broadband noise stimuli, and a few units were also tested at other frequencies within the cell's tuning response area. 2. When tested at stimulus intensities 20-30 dB above CF or noise threshold, the different forms of azimuthal sensitivity exhibited by AI neurons could be divided into (1) contra-field azimuth functions; (2) ipsi-field functions; (3) central-field functions; (4) omnidirectional functions, and (5) multipeaked functions. Contra-field azimuth functions were the most prevalent, with 45.9% of units tested with CF tones and 42.9% of units tested with noise exhibiting this type of azimuthal sensitivity. Ipsi-field azimuthal sensitivity was found in 16.9% of units tested with CF tones and 19.8% of units tested with noise. Central-field azimuthal sensitivity was seen in 10.8% of units tested with CF tones and 17.6% of units tested with noise. Omnidirectional azimuthal sensitivity was seen in 19.9% of units tested with CF tones and 17.6% of units tested with noise, whereas multipeaked azimuthal sensitivity was found in 6.5% of units tested with CF tones and 5.5% of units tested with noise. 3. The effects of increasing stimulus intensity on azimuthal sensitivity were examined in 185 units tested with CF tones and 67 units tested with noise. For four major classes of azimuthal sensitivity (contra-field, ipsi-field, central-field and omnidirectional), the most common effect (approximately 60% of each class) was for the azimuth function to remain constant in form by the defining criteria for these classes. The next most common effect for all classes except omnidirectional azimuth functions was for an expansion of the azimuthal range eliciting responses. (The definition of omnidirectionality precluded any expansion of the response range in this class of azimuth function). A smaller number of units in some classes showed a compression of the azimuth function to a smaller response range, and others showed more complex expansive and compressive effects with increasing stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)

Topography of excitatory bandwidth in cat primary auditory cortex: single-neuron versus multiple-neuron recordings

1992 ◽  
Vol 68 (5) ◽  
pp. 1487-1502 ◽  
Author(s):  
C. E. Schreiner ◽  
M. L. Sutter
Keyword(s):  
Spatial Distribution ◽  
Auditory Cortex ◽  
Single Neuron ◽  
Primary Auditory Cortex ◽  
Single Neurons ◽  
Minimum Threshold ◽  
Multiple Unit ◽  
The Individual ◽  
Multiple Units ◽  
Ventral Border

1. The spatial distribution of the sharpness of tuning of single neurons along the dorsoventral extent of primary auditory cortex (AI) was studied. A sharpness of tuning gradient was initially obtained with multiple-unit recordings, and in combination with the cochleotopic organization, served as a frame of reference for the locations of single neurons. The frequency selectivity or "integrated excitatory bandwidth" of multiple units varied systematically along the dorsoventral extent of AI. The most sharply tuned unit clusters were found at the approximate center of the dorsoventral extent. A gradual broadening of the integrated excitatory bandwidth in both dorsal and ventral directions was consistently seen. 2. The multiple-unit measures of the bandwidth 10 (BW10) and 40 dB (BW40) above minimum threshold, pooled across several animals and expressed in octaves, were similar to those described within individual cases in cats. As in the individual animals, the bandwidth maps were V shaped with minima located at the approximate center of the dorsal-ventral extent of AI. The location of the minimum in the multiple-unit bandwidth map (i.e., the most sharply tuned area) was used as a reference point to pool single-neuron data across animals. 3. For single neurons, the dorsal half of the BW40 distribution showed a gradient paralleling that found for multiple units. For both single and multiple units, the average excitatory bandwidth increased at a rate of approximately 0.27 octaves/mm from the center of AI toward the dorsal fringe. Differing from the dorsal half of AI, the ventral half of AI showed no clear BW40 gradient for single units along its dorsoventral extent. At 40 dB above minimum threshold, most ventral neurons encountered were sharply tuned. By contrast, the multiple-unit BW40 showed a gradient similar to the dorsal half with 0.23 octaves/mm increasing from the center toward the ventral border of AI. 4. For single neurons, BW10 showed no clear systematic spatial distribution in AI. Neither the dorsal nor the ventral gradient was significantly different from zero slope, although the dorsal half showed a trend toward increasing BW10s. Contrasting single neurons, both dorsal and ventral halves of AI showed BW10 slopes for multiple units confirming a V-shaped map of the integrated excitatory bandwidth within the dorsoventral extent of AI. 5. On the basis of the distribution of the integrated (multiple-unit) excitatory bandwidth, AI was parceled into three regions: the dorsal gradient, the ventral gradient, and the central, narrowly tuned area.(ABSTRACT TRUNCATED AT 400 WORDS)

Tonotopic and functional organization in the auditory cortex of the big brown bat, Eptesicus fuscus

1993 ◽  
Vol 70 (5) ◽  
pp. 1988-2009 ◽  
Author(s):  
S. P. Dear ◽  
J. Fritz ◽  
T. Haresign ◽  
M. Ferragamo ◽  
J. A. Simmons
Keyword(s):  
Auditory Cortex ◽  
Surface Area ◽  
Cortical Neurons ◽  
Functional Organization ◽  
Primary Auditory Cortex ◽  
Target Range ◽  
Cortical Surface ◽  
Behavioral Experiments ◽  
Cortical Surface Area ◽  
Harmonic Ratio

1. In Eptesicus the auditory cortex, as defined by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps, encompasses an average cortical surface area of 5.7 mm2. This area is large with respect to the total cortical surface area and reflects the importance of auditory processing to this species of bat. 2. The predominant pattern of organization in response to tone bursts observed in each cortex is tonotopic, with three discernible divisions revealed by our data. However, although cortical best-frequency (BF) maps from most of the individual bats are similar, no two maps are identical. The largest division contains an average of 84% of the auditory cortical surface area, with BF tonotopically mapped from high to low along the anteroposterior axis and is part of the primary auditory cortex. The medium division encompasses an average of 13% of the auditory cortical surface area, with highly variable BF organization across bats. The third region is the smallest, with an average of only 3% of auditory cortical surface area and is located at the anterolateral edge of the cortex. This region is marked by a reversal of the tonotopic axis and a restriction in the range of BFs as compared with the larger, tonotopically organized division. 3. A population of cortical neurons was found (n = 39) in which each neuron exhibited two BF threshold minima (BF1 and BF2) in response to tone bursts. These neurons thus have multipeaked frequency threshold tuning curves. In Eptesicus the majority of multipeaked frequency-tuned neurons (n = 27) have threshold minima at frequencies that correspond to a harmonic ratio of three-to-one. In contrast, the majority of multipeaked neurons in cats have threshold minima at frequencies in a ratio of three-to-two. A three-to-one harmonic ratio corresponds to the "spectral notches" produced by interference between overlapping echoes from multiple reflective surfaces in complex sonar targets. Behavioral experiments have demonstrated the ability of Eptesicus to use spectral interference notches for perceiving target shape, and this subpopulation of multipeaked frequency-tuned neurons may be involved in coding of spectral notches. 4. The auditory cortex contains delay-tuned neurons that encode target range (n = 99). Most delay-tuned neurons respond poorly to tones or individual FM sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned.(ABSTRACT TRUNCATED AT 400 WORDS)

Single-Neuron Responses to Rapidly Presented Temporal Sequences in the Primary Auditory Cortex of the Awake Macaque Monkey

2007 ◽  
Vol 97 (2) ◽  
pp. 1726-1737 ◽  
Author(s):  
M. L. Phan ◽  
G. H. Recanzone
Keyword(s):  
Auditory Cortex ◽  
Cortical Neurons ◽  
Primary Auditory Cortex ◽  
Macaque Monkey ◽  
Auditory Task ◽  
Single Neurons ◽  
Animal Vocalizations ◽  
Early Processing ◽  
The Individual ◽  
Temporal Rate

One fundamental process of the auditory system is to process rapidly occurring acoustic stimuli, which are fundamental components of complex stimuli such as animal vocalizations and human speech. Although the auditory cortex is known to subserve the perception of acoustic temporal events, relatively little is currently understood about how single neurons respond to such stimuli. We recorded the responses of single neurons in the primary auditory cortex of alert monkeys performing an auditory task. The stimuli consisted of four tone pips with equal duration and interpip interval, with the first and last pip of the sequence being near the characteristic frequency of the neuron under study. We manipulated the rate of presentation, the frequency of the middle two tone pips, and the order by which they were presented. Our results indicate that single cortical neurons are ineffective at responding to the individual tone pips of the sequence for pip durations of <12 ms, but did begin to respond synchronously to each pip of the sequence at 18-ms durations. In addition, roughly 40% of the neurons tested were able to discriminate the order that the two middle tone pips were presented in at durations of ≥24 ms. These data place the primate primary auditory cortex at an early processing stage of temporal rate discrimination.

Functional organization of sound direction and sound pressure level in primary auditory cortex of the cat

1994 ◽  
Vol 72 (5) ◽  
pp. 2383-2405 ◽  
Author(s):  
J. C. Clarey ◽  
P. Barone ◽  
T. J. Imig
Keyword(s):  
Auditory Cortex ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Functional Organization ◽  
Primary Auditory Cortex ◽  
Pressure Level ◽  
Cortical Surface ◽  
Data Set ◽  
Function Type ◽  
Level Function

1. The functional organization of neuronal tuning to the azimuthal location and sound pressure level (SPL) of noise bursts was studied in high-frequency primary auditory cortex (AI) of barbiturate-anesthetized cats. Three data collection strategies were used to map neural responses: 1) electrode penetrations oriented normal to the cortical surface provided information on the radial organization of neurons' responses; 2) neurons' responses were examined at a few points in the middle cortical layers in multiple normal penetrations across AI to produce fine-grain maps of azimuth and level selectivity; and 3) electrode penetrations oriented tangential to the cortical surface provided information on neurons' responses along the isofrequency dimension. 2. An azimuth-level data set was obtained for each single- or multiple- (multi-) unit recording; this consisted of responses to noise bursts at five SPLs (0–80 dB in 20-dB steps) from seven azimuthal locations in the frontal hemifield (-90 to +90 degrees in 30 degrees steps; 0 degree elevation). An azimuth function was derived from these data by averaging response magnitude over all SPLs at each azimuth tested. A preferred azimuth range (PAR; range of azimuths over which the response was > or = 75% of maximum) was calculated from the azimuth function and provided a level-independent measure of azimuth selectivity. Each PAR was assigned to one of four azimuth preference categories (contralateral-, midline-, ipsilateral-preferring, or broad/multipeaked) according to its location and extent. A level function obtained from the data set (responsiveness averaged over all azimuths) was classified as monotonic if it showed a decrease of < or = 25% (relative to maximum) at the highest SPL tested (usually 80 dB), and nonmonotonic if it showed a decrease of > 25%. The percentage reduction in responsiveness, relative to maximum, at the highest level tested (termed nonmonotonic strength) and the preferred level range (PLR; range of SPLs over which responsiveness was > or = 75% of maximum) of each response was also determined. 3. Normal penetrations typically showed a predominance of one azimuth preference category and/or level function type. The majority of penetrations (26/36: 72.2%) showed statistically significant azimuth preference homogeneity, and approximately one-half (17/36: 47.2%) showed significant level function type homogeneity. Over one-third (13/36) showed significant homogeneity for both azimuth preference and level function type. 4. Mapping experiments (n = 4) sampled the azimuth and level response functions at two or more depths in closely spaced normal penetrations that covered several square millimeters of AI.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional topography of cat primary auditory cortex: distribution of integrated excitation

1990 ◽  
Vol 64 (5) ◽  
pp. 1442-1459 ◽  
Author(s):  
C. E. Schreiner ◽  
J. R. Mendelson
Keyword(s):  
Spatial Distribution ◽  
Auditory Cortex ◽  
Functional Organization ◽  
Primary Auditory Cortex ◽  
Response Magnitude ◽  
Response Threshold ◽  
Step Response ◽  
Frequency Independent ◽  
Multiple Unit ◽  
Excitatory Responses

1. Neuronal responses to tones and transient stimuli were mapped with microelectrodes in the primary auditory cortex (AI) of barbiturate anesthetized cats. Most of the dorsoventral extent of AI was mapped with multiple-unit recordings in the high-frequency domain (between 5.8 and 26.3 kHz) of all six studied cases. The spatial distributions of 1) sharpness of tuning measured with pure tones and 2) response magnitudes to a broadband transient were determined in each of three intensively studied cases. 2. The sharpness of tuning of integrated cluster responses was defined 10 dB above threshold (Q10 dB, integrated excitatory bandwidth). The spatial reconstructions revealed a frequency-independent maximum located near the center of the dorsoventral extent of AI. The sharpness of tuning gradually decreased toward the dorsal and ventral border of AI in all three cases. 3. The sharpness of tuning 40 dB above response threshold was also analyzed (Q40 dB). The Q40 dB values were less than one-half of the corresponding Q10 dB value. The spatial distribution showed a maximum in the center of AI, similar to the Q10 dB distribution. In two out of three cases, restricted additional maxima were recorded dorsal to the main maximum. Overall, Q10 dB and Q40 dB were only moderately correlated, indicating that the integrated excitatory bandwidth at higher stimulus levels can be influenced by additional mechanisms that are not active at lower levels. 4. The magnitude of excitatory responses to a broadband transient (frequency-step response) was determined. The normalized response magnitude varied between less than 1% and up to 100% relative to a characteristic frequency (CF) tone response. The step-response magnitude showed a systematic spatial distribution. An area dorsal to the Q10 dB maximum consistently showed the largest response magnitude surrounded by areas of lower responsivity. A second spatially more restricted maximum was recorded in the ventral-third of each map. Areas with high-transient responsiveness coincided with areas of broad integrated excitatory bandwidth at comparable stimulus levels. 5. The distribution of excitation produced by narrowband and broadband signals suggest that there exists a clear functional organization in the isofrequency domain of AI that is orthogonal to the main cochleotopic organization of the AI. Systematic spatial variations of the integrated excitatory bandwidth reflect underlying cortical processing capacities that may contribute to a parallel analysis of spectral complexity, e.g., spectral shape and contrast, at any given frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Listening Through Different Ears Alters Spatial Response Fields in Ferret Primary Auditory Cortex

2001 ◽  
Vol 86 (2) ◽  
pp. 1043-1046 ◽  
Author(s):  
Thomas D. Mrsic-Flogel ◽  
Andrew J. King ◽  
Rick L. Jenison ◽  
Jan W. H. Schnupp
Keyword(s):  
Individual Differences ◽  
Auditory Cortex ◽  
Space Perception ◽  
Primary Auditory Cortex ◽  
Spatial Cues ◽  
Sound Sources ◽  
Auditory Space ◽  
Acoustical Properties ◽  
Spatial Response ◽  
The Individual

The localization of sounds in space is based on spatial cues that arise from the acoustical properties of the head and external ears. Individual differences in localization cue values result from variability in the shape and dimensions of these structures. We have mapped spatial response fields of high-frequency neurons in ferret primary auditory cortex using virtual sound sources based either on the animal's own ears or on the ears of other subjects. For 73% of units, the response fields measured using the animals' own ears differed significantly in shape and/or position from those obtained using spatial cues from another ferret. The observed changes correlated with individual differences in the acoustics. These data are consistent with previous reports showing that humans localize less accurately when listening to virtual sounds from other individuals. Together these findings support the notion that neural mechanisms underlying auditory space perception are calibrated by experience to the properties of the individual.

Sign in / Sign up

Export Citation Format

Share Document