scholarly journals Sound Localization During Homotopic and Heterotopic Bilateral Cooling Deactivation of Primary and Nonprimary Auditory Cortical Areas in the Cat

2007 ◽  
Vol 97 (1) ◽  
pp. 26-43 ◽  
Author(s):  
Shveta Malhotra ◽  
Stephen G. Lomber
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Broad Band ◽  
Acoustic Stimulus ◽  
Primary Auditory Cortex ◽  
Orienting Response ◽  
Normal Function ◽  
Anterior Ectosylvian Sulcus ◽  
Accurate Localization ◽  
Auditory Field

Although the contributions of primary auditory cortex (AI) to sound localization have been extensively studied in a large number of mammals, little is known of the contributions of nonprimary auditory cortex to sound localization. Therefore the purpose of this study was to examine the contributions of both primary and all the recognized regions of acoustically responsive nonprimary auditory cortex to sound localization during both bilateral and unilateral reversible deactivation. The cats learned to make an orienting response (head movement and approach) to a 100-ms broad-band noise stimulus emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90° to right 90°, at 15° intervals) along the horizontal plane after attending to a central visual stimulus. Twenty-one cats had one or two bilateral pairs of cryoloops chronically implanted over one of ten regions of auditory cortex. We examined AI [which included the dorsal zone (DZ)], the three other tonotopic fields [anterior auditory field (AAF), posterior auditory field (PAF), ventral posterior auditory field (VPAF)], as well as six nontonotopic regions that included second auditory cortex (AII), the anterior ectosylvian sulcus (AES), the insular (IN) region, the temporal (T) region [which included the ventral auditory field (VAF)], the dorsal posterior ectosylvian (dPE) gyrus [which included the intermediate posterior ectosylvian (iPE) gyrus], and the ventral posterior ectosylvian (vPE) gyrus. In accord with earlier studies, unilateral deactivation of AI/DZ caused sound localization deficits in the contralateral field. Bilateral deactivation of AI/DZ resulted in bilateral sound localization deficits throughout the 180° field examined. Of the three other tonotopically organized fields, only deactivation of PAF resulted in sound localization deficits. These deficits were virtually identical to the unilateral and bilateral deactivation results obtained during AI/DZ deactivation. Of the six nontonotopic regions examined, only deactivation of AES resulted in sound localization deficits in the contralateral hemifield during unilateral deactivation. Although bilateral deactivation of AI/DZ, PAF, or AES resulted in profound sound localization deficits throughout the entire field, the cats were generally able to orient toward the hemifield that contained the acoustic stimulus, but not accurately identify the location of the stimulus. Neither unilateral nor bilateral deactivation of areas AAF, VPAF, AII, IN, T, dPE, nor vPE had any effect on the sound localization task. Finally, bilateral heterotopic deactivations of AI/DZ, PAF, or AES yielded deficits that were as profound as bilateral homotopic cooling of any of these sites. The fact that deactivation of any one region (AI/DZ, PAF, or AES) was sufficient to produce a deficit indicated that normal function of all three regions was necessary for normal sound localization. Neither unilateral nor bilateral deactivation of AI/DZ, PAF, or AES affected the accurate localization of a visual target. The results suggest that hemispheric deactivations contribute independently to sound localization deficits.

Cortical Control of Sound Localization in the Cat: Unilateral Cooling Deactivation of 19 Cerebral Areas

2004 ◽  
Vol 92 (3) ◽  
pp. 1625-1643 ◽  
Author(s):  
Shveta Malhotra ◽  
Amee J. Hall ◽  
Stephen G. Lomber
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Broad Band ◽  
Acoustic Stimulus ◽  
Anterior Ectosylvian Sulcus ◽  
Area 5 ◽  
Area 6 ◽  
Auditory Field ◽  
Lateral Area ◽  
Medial Area

We examined the ability of mature cats to accurately orient to, and approach, an acoustic stimulus during unilateral reversible cooling deactivation of primary auditory cortex (AI) or 1 of 18 other cerebral loci. After attending to a central visual stimulus, the cats learned to orient to a 100-ms broad-band, white-noise stimulus emitted from a central speaker or 1 of 12 peripheral sites (at 15° intervals) positioned along the horizontal plane. Twenty-eight cats had two to six cryoloops implanted over multiple cerebral loci. Within auditory cortex, unilateral deactivation of AI, the posterior auditory field (PAF) or the anterior ectosylvian sulcus (AES) resulted in orienting deficits throughout the contralateral field. However, unilateral deactivation of the anterior auditory field, the second auditory cortex, or the ventroposterior auditory field resulted in no deficits on the orienting task. In multisensory cortex, unilateral deactivation of neither ventral or dorsal posterior ectosylvian cortices nor anterior or posterior area 7 resulted in any deficits. No deficits were identified during unilateral cooling of the five visual regions flanking auditory or multisensory cortices: posterior or anterior ii suprasylvian sulcus, posterior suprasylvian sulcus or dorsal or ventral posterior suprasylvian gyrus. In motor cortex, we identified contralateral orienting deficits during unilateral cooling of lateral area 5 (5L) or medial area 6 (6m) but not medial area 5 or lateral area 6. In a control visual-orienting task, areas 5L and 6m also yielded deficits to visual stimuli presented in the contralateral field. Thus the sound-localization deficits identified during unilateral deactivation of area 5L or 6m were not unimodal and are most likely the result of motor rather than perceptual impairments. Overall, three regions in auditory cortex (AI, PAF, AES) are critical for accurate sound localization as assessed by orienting.

Sound Localization Deficits During Reversible Deactivation of Primary Auditory Cortex and/or the Dorsal Zone

2008 ◽  
Vol 99 (4) ◽  
pp. 1628-1642 ◽  
Author(s):  
Shveta Malhotra ◽  
G. Christopher Stecker ◽  
John C. Middlebrooks ◽  
Stephen G. Lomber
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Primary Auditory Cortex ◽  
Noise Burst ◽  
Orienting Response ◽  
Error Rates ◽  
Broadband Noise ◽  
Physiological Data ◽  
Anterior Ectosylvian Sulcus ◽  
Auditory Field

We examined the contributions of primary auditory cortex (A1) and the dorsal zone of auditory cortex (DZ) to sound localization behavior during separate and combined unilateral and bilateral deactivation. From a central visual fixation point, cats learned to make an orienting response (head movement and approach) to a 100-ms broadband noise burst emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90° to right 90°, at 15° intervals) along the horizontal plane. Following training, each cat was implanted with separate cryoloops over A1 and DZ bilaterally. Unilateral deactivation of A1 or DZ or simultaneous unilateral deactivation of A1 and DZ (A1/DZ) resulted in spatial localization deficits confined to the contralateral hemifield, whereas sound localization to positions in the ipsilateral hemifield remained unaffected. Simultaneous bilateral deactivation of both A1 and DZ resulted in sound localization performance dropping from near-perfect to chance (7.7% correct) across the entire field. Errors made during bilateral deactivation of A1/DZ tended to be confined to the same hemifield as the target. However, unlike the profound sound localization deficit that occurs when A1 and DZ are deactivated together, deactivation of either A1 or DZ alone produced partial and field-specific deficits. For A1, bilateral deactivation resulted in higher error rates (performance dropping to ∼45%) but relatively small errors (mostly within 30° of the target). In contrast, bilateral deactivation of DZ produced somewhat fewer errors (performance dropping to only ∼60% correct), but the errors tended to be larger, often into the incorrect hemifield. Therefore individual deactivation of either A1 or DZ produced specific and unique sound localization deficits. The results of the present study reveal that DZ plays a role in sound localization. Along with previous anatomical and physiological data, these behavioral data support the view that A1 and DZ are distinct cortical areas. Finally, the findings that deactivation of either A1 or DZ alone produces partial sound localization deficits, whereas deactivation of either posterior auditory field (PAF) or anterior ectosylvian sulcus (AES) produces profound sound localization deficits, suggests that PAF and AES make more significant contributions to sound localization than either A1 or DZ.

What and How the Deaf Brain Sees

2019 ◽  
Vol 31 (8) ◽  
pp. 1091-1109 ◽  
Author(s):  
Caroline D. C. Alencar ◽  
Blake E. Butler ◽  
Stephen G. Lomber
Keyword(s):  
Auditory Cortex ◽  
Visual Processing ◽  
Sensory Modality ◽  
Primary Auditory Cortex ◽  
Visual Localization ◽  
Vernier Acuity ◽  
Anterior Ectosylvian Sulcus ◽  
Visual Functions ◽  
Auditory Field ◽  
The Brain

Over the past decade, there has been an unprecedented level of interest and progress into understanding visual processing in the brain of the deaf. Specifically, when the brain is deprived of input from one sensory modality (such as hearing), it often compensates with supranormal performance in one or more of the intact sensory systems (such as vision). Recent psychophysical, functional imaging, and reversible deactivation studies have converged to define the specific visual abilities that are enhanced in the deaf, as well as the cortical loci that undergo crossmodal plasticity in the deaf and are responsible for mediating these superior visual functions. Examination of these investigations reveals that central visual functions, such as object and facial discrimination, and peripheral visual functions, such as motion detection, visual localization, visuomotor synchronization, and Vernier acuity (measured in the periphery), are specifically enhanced in the deaf, compared with hearing participants. Furthermore, the cortical loci identified to mediate these functions reside in deaf auditory cortex: BA 41, BA 42, and BA 22, in addition to the rostral area, planum temporale, Te3, and temporal voice area in humans; primary auditory cortex, anterior auditory field, dorsal zone of auditory cortex, auditory field of the anterior ectosylvian sulcus, and posterior auditory field in cats; and primary auditory cortex and anterior auditory field in both ferrets and mice. Overall, the findings from these studies show that crossmodal reorganization in auditory cortex of the deaf is responsible for the superior visual abilities of the deaf.

Inactivation of the DSCF area of the auditory cortex with muscimol disrupts frequency discrimination in the mustached bat

1992 ◽  
Vol 68 (5) ◽  
pp. 1613-1623 ◽  
Author(s):  
H. Riquimaroux ◽  
S. J. Gaioni ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Doppler Shift ◽  
Broad Band ◽  
Primary Auditory Cortex ◽  
Tone Burst ◽  
Signal Pulse ◽  
Gamma Aminobutyric Acid ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Leg Flexion

1. The Jamaican mustached bat uses a biosonar signal (pulse) with eight major components: four harmonics each consisting of a long constant frequency (CF1-4) component followed by a short frequency-modulated (FM1-4) component. While flying, the bat adjusts the frequency of its pulse so as to maintain the CF2 of the Doppler-shifted echo at a frequency to which its cochlea is very sharply tuned. This Doppler shift (DS) compensation likely is mediated or influenced by the Doppler-shifted CF (DSCF) processing area of the primary auditory cortex, which only represents frequencies in the range of echo CF2s (60.6 to 62.3 kHz when the "resting" frequency of the CF2 is 61.0 kHz). 2. We trained four bats to discriminate between different trains of paired tone bursts that mimicked a bat's pulse CF2 and the accompanying echo CF2. The frequency of these CF2s ranged between 61.0 and 64.0 kHz. A discriminated shock avoidance procedure response was employed using a leg flexion. For one stimulus, the S+, the pulse and echo CF2s were the same frequency (delta f = 0, i.e., no Doppler shift). A leg flexion during the S+ turned off both the S+ and the scheduled shock. For a second stimulus, the S-, the echo CF2 was 0.05, 0.1, 0.3, 0.5, or 2.0 kHz higher than the pulse CF2. A delta f of 0.05 kHz was a frequency difference of 0.08%. No shock followed the S-, and leg flexions had no consequences. Correct responses consisted of a leg flexion during the S+ and no flexion during the S-; these responses were added together to compute the percentage of correct responses. When a bat correctly responded at better than 75% for all the delta f s, muscimol, a potent agonist of gamma-aminobutyric acid, was bilaterally applied to inactivate the DSCF area. Performance on each delta f discrimination was then measured. 3. Initial attempts to condition the bats to flex their legs to the CF tones mimicking part of the natural pulses and echoes failed. When broad-band noise bursts were substituted, however, the conditioned response was rapidly established. The noise band-width was gradually reduced and then replaced with the CF tones. Discrimination training with the tone burst trains then commenced. Throughout this procedure, the bats maintained their responding to the stimuli. The bats typically required approximately 20-30 sessions to perform consistently (> or = 75% correct responses) a discrimination involving a 2 kHz delta f.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Reciprocal connectivity between secondary auditory cortical field and amygdala in mice

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Hiroaki Tsukano ◽  
Xubin Hou ◽  
Masao Horie ◽  
Hiroki Kitaura ◽  
Nana Nishio ◽  
...  
Keyword(s):  
Auditory Cortex ◽  
Primary Auditory Cortex ◽  
The Other ◽  
Axon Terminals ◽  
Reciprocal Connections ◽  
Cholera Toxin Subunit B ◽  
Auditory Field ◽  
Subunit B ◽  
Cortical Field ◽  
Feedback Pathway

AbstractRecent studies have examined the feedback pathway from the amygdala to the auditory cortex in conjunction with the feedforward pathway from the auditory cortex to the amygdala. However, these connections have not been fully characterized. Here, to visualize the comprehensive connectivity between the auditory cortex and amygdala, we injected cholera toxin subunit b (CTB), a bidirectional tracer, into multiple subfields in the mouse auditory cortex after identifying the location of these subfields using flavoprotein fluorescence imaging. After injecting CTB into the secondary auditory field (A2), we found densely innervated CTB-positive axon terminals that were mainly located in the lateral amygdala (La), and slight innervations in other divisions such as the basal amygdala. Moreover, we found a large number of retrogradely-stained CTB-positive neurons in La after injecting CTB into A2. When injecting CTB into the primary auditory cortex (A1), a small number of CTB-positive neurons and axons were visualized in the amygdala. Finally, we found a near complete absence of connections between the other auditory cortical fields and the amygdala. These data suggest that reciprocal connections between A2 and La are main conduits for communication between the auditory cortex and amygdala in mice.

Unit study of monkey frontal cortex: active localization of auditory and of visual stimuli

1986 ◽  
Vol 56 (4) ◽  
pp. 934-952 ◽  
Author(s):  
E. Vaadia ◽  
D. A. Benson ◽  
R. D. Hienz ◽  
M. H. Goldstein
Keyword(s):  
Auditory Cortex ◽  
Frontal Cortex ◽  
Broad Band ◽  
Primary Auditory Cortex ◽  
Auditory Localization ◽  
Visual Localization ◽  
Spatial Tuning ◽  
Active Localization ◽  
Localization Conditions ◽  
Localization Behavior

The influence of sound localization behavior on unit activity in the frontal cortex of awake rhesus monkeys was examined by comparing responses under three behavioral conditions: auditory localization, during which a response was required to the location of a sound (broad-band noise) source; auditory detect, during which a response was required to indicate the occurrence of the sound regardless of location; visual localization, during which no sounds were presented and a response was required to the location of a visual stimulus; and nonperform, presentation of auditory stimuli as in the first two conditions, but with the animal sitting passively. Extracellular microelectrode recordings were made in the periarcuate region and dorsal and ventral prefrontal areas near the principal sulcus. Four monkeys were used with a total of 498 cells studied. Of the total population, only five cells were found to have characteristics similar to those of auditory units in the primary auditory cortex and the surrounding belt area. More typically, units were found that had strong short-latency responses specific to the auditory and/or visual localization tasks. These units had no or weak responses when the same sound stimuli were presented in the auditory detect task or when a monkey received the sound stimuli in a nonperforming condition. Two regions were identified, one medial and/or posterior to the arcuate sulcus, in Brodmann's area 6; the second included parts of areas 8 and 9 within the genu of the arcuate sulcus. Units from these regions are referred to, respectively, as the postarcuate and the prearcuate populations. Both populations responded predominantly during active localization behavior. Sixty-two percent of the postarcuate population responded during auditory localization, 32% responded during auditory detect, and only 18% responded to acoustic stimuli presented in the nonperforming condition. In the prearcuate population percentages in these three conditions were 35, 25, and 12%, respectively. For visual localization, 54% in the postarcuate population responded, whereas 42% in the prearcuate responded. Spatial tuning of units during auditory localization was similar to that seen in units of the primary auditory cortex, with the greatest percentages of units responding to stimuli contralateral to the recording site. Similar tuning was observed for the visual localization task as well. Similarities in spatial tuning between the auditory and visual localization conditions were examined to assess the "bimodal" nature of the units.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Dissociable influences of primary auditory cortex and the posterior auditory field on neuronal responses in the dorsal zone of auditory cortex

2015 ◽  
Vol 113 (2) ◽  
pp. 475-486
Author(s):  
Melanie A. Kok ◽  
Daniel Stolzberg ◽  
Trecia A. Brown ◽  
Stephen G. Lomber
Keyword(s):  
Auditory Cortex ◽  
Receptive Fields ◽  
Primary Auditory Cortex ◽  
Population Level ◽  
Noise Burst ◽  
Hierarchical Organization ◽  
Neuronal Responses ◽  
Tone Frequency ◽  
Hierarchical Processing ◽  
Auditory Field

Current models of hierarchical processing in auditory cortex have been based principally on anatomical connectivity while functional interactions between individual regions have remained largely unexplored. Previous cortical deactivation studies in the cat have addressed functional reciprocal connectivity between primary auditory cortex (A1) and other hierarchically lower level fields. The present study sought to assess the functional contribution of inputs along multiple stages of the current hierarchical model to a higher order area, the dorsal zone (DZ) of auditory cortex, in the anaesthetized cat. Cryoloops were placed over A1 and posterior auditory field (PAF). Multiunit neuronal responses to noise burst and tonal stimuli were recorded in DZ during cortical deactivation of each field individually and in concert. Deactivation of A1 suppressed peak neuronal responses in DZ regardless of stimulus and resulted in increased minimum thresholds and reduced absolute bandwidths for tone frequency receptive fields in DZ. PAF deactivation had less robust effects on DZ firing rates and receptive fields compared with A1 deactivation, and combined A1/PAF cooling was largely driven by the effects of A1 deactivation at the population level. These results provide physiological support for the current anatomically based model of both serial and parallel processing schemes in auditory cortical hierarchical organization.

Correlation Between the Activity of Single Auditory Cortical Neurons and Sound-Localization Behavior in the Macaque Monkey

2000 ◽  
Vol 83 (5) ◽  
pp. 2723-2739 ◽  
Author(s):  
Gregg H. Recanzone ◽  
Darren C. Guard ◽  
Mimi L. Phan ◽  
Tien-I K. Su
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Cortical Neurons ◽  
Primary Auditory Cortex ◽  
Macaque Monkey ◽  
Auditory Space ◽  
Spatial Sensitivity ◽  
Acoustic Space ◽  
Localization Ability ◽  
Primate Cerebral Cortex

Lesion studies have indicated that the auditory cortex is crucial for the perception of acoustic space, yet it remains unclear how these neurons participate in this perception. To investigate this, we studied the responses of single neurons in the primary auditory cortex (AI) and the caudomedial field (CM) of two monkeys while they performed a sound-localization task. Regression analysis indicated that the responses of ∼80% of neurons in both cortical areas were significantly correlated with the azimuth or elevation of the stimulus, or both, which we term “spatially sensitive.” The proportion of spatially sensitive neurons was greater for stimulus azimuth compared with stimulus elevation, and elevation sensitivity was primarily restricted to neurons that were tested using stimuli that the monkeys also could localize in elevation. Most neurons responded best to contralateral speaker locations, but we also encountered neurons that responded best to ipsilateral locations and neurons that had their greatest responses restricted to a circumscribed region within the central 60° of frontal space. Comparing the spatially sensitive neurons with those that were not spatially sensitive indicated that these two populations could not be distinguished based on either the firing rate, the rate/level functions, or on their topographic location within AI. Direct comparisons between the responses of individual neurons and the behaviorally measured sound-localization ability indicated that proportionally more neurons in CM had spatial sensitivity that was consistent with the behavioral performance compared with AI neurons. Pooling the responses across neurons strengthened the relationship between the neuronal and psychophysical data and indicated that the responses pooled across relatively few CM neurons contain enough information to account for sound-localization ability. These data support the hypothesis that auditory space is processed in a serial manner from AI to CM in the primate cerebral cortex.

Spectrotemporal Structure of Receptive Fields in Areas AI and AAF of Mouse Auditory Cortex

2003 ◽  
Vol 90 (4) ◽  
pp. 2660-2675 ◽  
Author(s):  
Jennifer F. Linden ◽  
Robert C. Liu ◽  
Maneesh Sahani ◽  
Christoph E. Schreiner ◽  
Michael M. Merzenich
Keyword(s):  
Receptive Field ◽  
Auditory Cortex ◽  
Receptive Fields ◽  
Primary Auditory Cortex ◽  
Dynamic Stimuli ◽  
Tuning Curves ◽  
Response Characteristics ◽  
Spectrotemporal Receptive Fields ◽  
Auditory Field ◽  
Tonal Stimuli

The mouse is a promising model system for auditory cortex research because of the powerful genetic tools available for manipulating its neural circuitry. Previous studies have identified two tonotopic auditory areas in the mouse—primary auditory cortex (AI) and anterior auditory field (AAF)— but auditory receptive fields in these areas have not yet been described. To establish a foundation for investigating auditory cortical circuitry and plasticity in the mouse, we characterized receptive-field structure in AI and AAF of anesthetized mice using spectrally complex and temporally dynamic stimuli as well as simple tonal stimuli. Spectrotemporal receptive fields (STRFs) were derived from extracellularly recorded responses to complex stimuli, and frequency-intensity tuning curves were constructed from responses to simple tonal stimuli. Both analyses revealed temporal differences between AI and AAF responses: peak latencies and receptive-field durations for STRFs and first-spike latencies for responses to tone bursts were significantly longer in AI than in AAF. Spectral properties of AI and AAF receptive fields were more similar, although STRF bandwidths were slightly broader in AI than in AAF. Finally, in both AI and AAF, a substantial minority of STRFs were spectrotemporally inseparable. The spectrotemporal interaction typically appeared in the form of clearly disjoint excitatory and inhibitory subfields or an obvious spectrotemporal slant in the STRF. These data provide the first detailed description of auditory receptive fields in the mouse and suggest that although neurons in areas AI and AAF share many response characteristics, area AAF may be specialized for faster temporal processing.

Contribution of auditory cortex to sound localization by the ferret (Mustela putorius)

1987 ◽  
Vol 57 (6) ◽  
pp. 1746-1766 ◽  
Author(s):  
G. L. Kavanagh ◽  
J. B. Kelly
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Horizontal Plane ◽  
Primary Auditory Cortex ◽  
Cortical Lesions ◽  
Mustela Putorius ◽  
Complete Destruction ◽  
Left And Right ◽  
The Right ◽  
Bilateral Lesions

Ferrets were tested in a semicircular apparatus to determine the effects of auditory cortical lesions on their ability to localize sounds in space. They were trained to initiate trials while facing forward in the apparatus, and sounds were presented from one of two loudspeakers located in the horizontal plane. Minimum audible angles were obtained for three different positions, viz., the left hemifield, with loudspeakers centered around -60 degrees azimuth; the right hemifield, with loudspeakers centered around +60 degrees azimuth; and the midline with loudspeakers centered around 0 degrees azimuth. Animals with large bilateral lesions had severe impairments in localizing a single click in the midline test. Following complete destruction of the auditory cortex performance was only marginally above the level expected by chance even at large angles of speaker separation. Severe impairments were also found in localization of single clicks in both left and right lateral fields. In contrast, bilateral lesions restricted to the primary auditory cortex resulted in minimal impairments in midline localization. The same lesions, however, produced severe impairments in localization of single clicks in both left and right lateral fields. Large unilateral lesions that destroyed auditory cortex in one hemisphere resulted in an inability to localize single clicks in the contralateral hemifield. In contrast, no impairments were found in the midline test or in the ipsilateral hemifield. Unilateral lesions of the primary auditory cortex resulted in severe contralateral field deficits equivalent to those seen following complete unilateral destruction of auditory cortex. No deficits were seen in either the midline or the ipsilateral tests.

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