Bilateral Lesions Of Auditory Cortex Research Articles

Dissociation of Detection and Discrimination of Pure Tones following Bilateral Lesions of Auditory Cortex

It is well known that damage to the peripheral auditory system causes deficits in tone detection as well as pitch and loudness perception across a wide range of frequencies. However, the extent to which to which the auditory cortex plays a critical role in these basic aspects of spectral processing, especially with regard to speech, music, and environmental sound perception, remains unclear. Recent experiments indicate that primary auditory cortex is necessary for the normally-high perceptual acuity exhibited by humans in pure-tone frequency discrimination. The present study assessed whether the auditory cortex plays a similar role in the intensity domain and contrasted its contribution to sensory versus discriminative aspects of intensity processing. We measured intensity thresholds for pure-tone detection and pure-tone loudness discrimination in a population of healthy adults and a middle-aged man with complete or near-complete lesions of the auditory cortex bilaterally. Detection thresholds in his left and right ears were 16 and 7 dB HL, respectively, within clinically-defined normal limits. In contrast, the intensity threshold for monaural loudness discrimination at 1 kHz was 6.5±2.1 dB in the left ear and 6.5±1.9 dB in the right ear at 40 dB sensation level, well above the means of the control population (left ear: 1.6±0.22 dB; right ear: 1.7±0.19 dB). The results indicate that auditory cortex lowers just-noticeable differences for loudness discrimination by approximately 5 dB but is not necessary for tone detection in quiet. Previous human and Old-world monkey experiments employing lesion-effect, neurophysiology, and neuroimaging methods to investigate the role of auditory cortex in intensity processing are reviewed.

Discrimination of brief speech sounds is impaired in rats with auditory cortex lesions

Auditory cortex (AC) lesions impair complex sound discrimination. However, a recent study demonstrated spared performance on an acoustic startle response test of speech discrimination following AC lesions (Floody et al., 2010). The current study reports the effects of AC lesions on two operant speech discrimination tasks. AC lesions caused a modest and quickly recovered impairment in the ability of rats to discriminate consonant–vowel–consonant speech sounds. This result seems to suggest that AC does not play a role in speech discrimination. However, the speech sounds used in both studies differed in many acoustic dimensions and an adaptive change in discrimination strategy could allow the rats to use an acoustic difference that does not require an intact AC to discriminate. Based on our earlier observation that the first 40ms of the spatiotemporal activity patterns elicited by speech sounds best correlate with behavioral discriminations of these sounds (Engineer et al., 2008), we predicted that eliminating additional cues by truncating speech sounds to the first 40ms would render the stimuli indistinguishable to a rat with AC lesions. Although the initial discrimination of truncated sounds took longer to learn, the final performance paralleled rats using full-length consonant–vowel–consonant sounds. After 20 days of testing, half of the rats using speech onsets received bilateral AC lesions. Lesions severely impaired speech onset discrimination for at least one-month post lesion. These results support the hypothesis that auditory cortex is required to accurately discriminate the subtle differences between similar consonant and vowel sounds.

Auditory Cortex is Important in the Extinction of Two Different Tone-Based Conditioned Fear Memories in Rats.

Extensive fear extinction research is guided by the view that there are structures in the brain that develop inhibitory control over the expression of conditioned fear memories. While the medial prefrontal cortex has recently captured attention as the locus of plasticity essential for extinction of conditioned fear, the auditory cortex is another plausible cortical area involved in extinction learning since it is considered a sufficient conditioned stimulus (CS) pathway in tone fear conditioning. We examined the role of auditory cortex in extinction of auditory-based fear memories with a standard tone-on conditioning, wherein a tone CS predicted a footshock unconditioned stimulus (US), or a novel tone-off conditioning, in which the tone was continually present and the offset of the tone was the CS predicting the US. Rats with bilateral auditory cortex lesions were trained in either paradigm and subsequently trained in extinction to the CS. Auditory cortex lesions had no effect on acquisition but impaired extinction to both CSs. These findings indicate that the auditory cortex contributes to extinction of wide-ranging auditory fear memories, as evidenced by deficits in both tone-on CS and tone-off CS extinction training.

The role of the auditory cortex in fear conditioning to complex auditory stimuli

Event Abstract Back to Event The role of the auditory cortex in fear conditioning to complex auditory stimuli Simon Rumpel1* 1 Research Institute of Molecular Pathology, Austria Auditory cued fear conditioning (AFC) is a widely used associative learning paradigm in which animals learn to associate a neutral stimulus (CS, conditioned stimulus), usually a pure tone, with an aversive stimulus (US, unconditioned stimulus), e.g. a foot shock. Subsequently, animals show fear-related behaviour when the CS is presented alone. In the amygdala, a putative site of tone-shock association, auditory and sensory input converge onto individual cells and projections from the amygdala to output brain areas, e.g. the brainstem, mediate fear behaviour. Auditory information reaches the amygdala via different pathways, a direct thalamic pathway and a more indirect thalamo-cortical pathway. Interestingly, AFC induces plastic changes in the auditory cortex, as neurons shift their frequency towards that of a pure tone CS. Hence, it is striking that the auditory cortex seems dispensable: AFC is not impaired in animals with a lesioned thalamo-cortical pathway. We probed the role of the auditory cortex in AFC in which the CS was a complex sound. We hypothesized that complex sounds may resemble sounds occurring in natural learning situations more closely than commonly used pure tones. AFC with a complex CS was feasible in wild type mice within one training session and created a robust, long lasting memory: In memory tests one or four days after training mice showed significant freezing levels during CS presentation compared to baseline. Bilateral auditory cortex lesions after training decreased acquired freezing levels to baseline levels, suggesting that the auditory cortex is involved in AFC with complex sounds in the intact brain. Importantly, also pre-training bilateral auditory cortex lesions abolished freezing to the complex CS. Despite these strong effects, lesioned animals could still be retrained to a pure tone CS. This finding demonstrates that the learning deficit following lesions was highly dependent on the features of the CS. AFC with a complex CS was not significantly impaired in mice with unilateral auditory cortex lesions. In a further series of experiments we aimed to elucidate principle features of complex CS that render the auditory cortex necessary for AFC. We used a frequency-modulated pure tone, an amplitude-modulated pure tone or a pseudo chord, which consisted of multiple constant frequencies. We observed that AFC with a pseudo chord showed strongest sensitivity to lesions, indicating that the auditory cortex may play a role in binding of simultaneous auditory information. Our findings emphasize how small changes in the experimental setup can lead to drastic changes in the brain circuits involved. Conference: 41st European Brain and Behaviour Society Meeting, Rhodes Island, Greece, 13 Sep - 18 Sep, 2009. Presentation Type: Oral Presentation Topic: Symposia lectures Citation: Rumpel S (2009). The role of the auditory cortex in fear conditioning to complex auditory stimuli. Conference Abstract: 41st European Brain and Behaviour Society Meeting. doi: 10.3389/conf.neuro.08.2009.09.049 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Jun 2009; Published Online: 05 Jun 2009. * Correspondence: Simon Rumpel, Research Institute of Molecular Pathology, Vienna, Austria, rumpel@imp.ac.at Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Simon Rumpel Google Simon Rumpel Google Scholar Simon Rumpel PubMed Simon Rumpel Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Detection of sinusoidal amplitude modulated sounds: Deficits after bilateral lesions of auditory cortex in the rat

The ability of rats to detect the presence of sinusoidal amplitude modulation (AM) of a broadband noise carrier was determined before and after bilateral ablation of auditory cortex. The rats were trained to withdraw from a drinking spout to avoid a shock when they detected a modulation of the sound. Sensitivity was evaluated by testing the rats at progressively smaller depths of modulation. Psychophysical curves were produced to describe the limits of detection at modulation rates of 10, 100 and 1000 Hz. Performance scores were based on the probability of withdrawal from the spout during AM (warning periods) relative to withdrawal during the un-modulated noise (safe periods). A threshold was defined as the depth of modulation that produced a score halfway between perfect avoidance and no avoidance (performance score = 0.5). Bilateral auditory cortical lesions resulted in significant elevations in threshold for detection of AM at rates of 100 and 1000 Hz. No significant shift was found at a modulation rate of 10 Hz. The magnitude of the deficit for AM rates of 100 and 1000 Hz was positively correlated with the size of the cortical lesion. Substantial deficits were found only in animals with lesions that included secondary as well as primary auditory cortical areas. The results show that the rat’s auditory cortex is important for processing sinusoidal AM and that its contribution is most apparent at high modulation rates. The data suggest that the auditory cortex is a crucial structure for maintaining normal sensitivity to temporal modulation of an auditory stimulus.

An investigation of sensory deficits underlying the aphasia-like behavior of macaques with auditory cortex lesions

Bilateral auditory cortex lesions in Japanese macaques result in an aphasia-like deficit in which the animals are unable to discriminate two forms of their coo vocalizations. To determine whether this deficit is sensory in nature, two monkeys with bilateral lesions were tested for their ability to discriminate frequency and frequency change. The results indicated that although the animals were able to discriminate between sounds of different frequencies, they were unable to determine whether a sound was changing in frequency. Because the animals' coo vocalizations differ primarily in the predominant direction of their frequency change and not in their absolute frequency content, the aphasia-like deficit of animals with bilateral auditory cortex lesions appears to be a sensory disorder.

Functional dissociations following bilateral lesions of auditory cortex

Functional dissociations following bilateral lesions of auditory cortex

Functional dissociations following bilateral lesions of auditory cortex

Functional dissociations following bilateral lesions of auditory cortex

Central Auditory Information Processing in Patients with Bilateral Auditory Cortex Lesions

Severe auditory cognitive disorders in 10 patients who had bilateral lesions either to the auditory cortex and/or auditory radiations were studied audiologically with special attention to residual hearing. This auditory cognitive problem is called “auditory agnosia or cortical deafness”. Our study revealed that auditory information processing for pure tones, monosyllable discrimination, environmental sound perception, and auditory comprehension is commonly but differently affected by bilateral lesions of auditory cortex or auditory radiation. In summary, these patients can discriminate loudness of pure tones and some environmental sounds but cannot clearly perceive any sounds of monosyllables and sentences. Generally their residual hearing is useful for auditory awareness and is often enhanced by lip reading.

Effects of bilateral auditory cortical lesions on gap-detection thresholds in the ferret (Mustela putorius).

Ferrets were tested for their ability to detect temporal gaps in noise before and after bilateral lesions of the primary auditory cortex. Thresholds for gap detection were determined first for normal animals with band-pass noises at various center frequencies (0.5 to 32 kHz) and at 8 kHz with various sound pressure levels (-10-70 dB). Gap-detection ability improved steadily as sound pressure increased up to 70 dB. No systematic relation was found between threshold and center frequency. To determine the effects of brain damage, ferrets were tested with 8-kHz band-pass noise at 70 dBSPL. After bilateral lesions of auditory cortex, ferrets were still capable of detecting gaps, but the mean threshold was elevated from 10.1 to 20.1 ms. The data demonstrate that auditory cortex is important for perceptual tasks requiring fine temporal resolution.

Effects of bilateral lesions of auditory cortex in mice on the acoustic startle response

The acoustic startle response (ASR) was used to investigate the effects of auditory cortical lesions on a brain stem-mediated auditory behavior. The ASRs were obtained longitudinally from young adult C57BL/6J mice before bilateral ablation of auditory cortex, 1 day after ablation, and 1 month later. Control mice received lesions of nonauditory cortex. For some mice, averaged brain stem-evoked responses (ABR) were obtained, and these indicated no effects of lesions on auditory sensitivity. One month after surgery, mice with auditory cortex ablations were statistically indistinguishable from controls on all suprathreshold measures of ASR. However, 1 day after ablation of auditory cortex, experimental animals (but not controls) exhibited a change in ASR amplitude (but not threshold or latency). When a noise burst of 80 dB SPL was used to elicit the ASR, the amplitude was diminished, but with a 110 dB stimulus, amplitude was enhanced. The findings can be interpreted in one of two ways: temporary interference with modulation of the ASR normally performed by auditory cortex; or a general effect of auditory cortex ablation on brain stem auditory circuits not specific to the ASR. In any event, if auditory cortex plays a modulatory role with regard to the ASR, it is apparently nonessential and/or readily compensated for after ablation.

Bilateral destruction of neocortical and perirhinal projection targets of the acoustic thalamus does not disrupt auditory fear conditioning

The present study examined whether complete bilateral destruction of auditory cortex would interfere with auditory fear conditioning in rats. Complete destruction of auditory cortex required lesions of temporal neocortical and perirhinal periallocortical areas. Fear conditioning was assessed by measuring freezing and arterial pressure responses elicited by an acoustic stimulus after pairing with footshock. Animals with complete bilateral lesions of auditory cortex showed conditioned arterial pressure and freezing responses comparable to those of unoperated controls. In contrast, bialteral destruction of the acoustic thalamus interfered with the conditioning of both responses. These results demonstrate that the auditory cortex is not required for the conditioning of fear responses to simple acoustic stimuli and add to the growing body of evidence that fear conditioning can be mediated by subcortical (amygdaloid) projections of the acoustic thalamus.

Effect of bilateral auditory cortex lesions on sound localization in Japanese macaques

1. The ability of four Japanese macaques (Macaca fuscata) to localize sound was determined after bilateral ablation of auditory cortex. The animals were given two tests: a "midline" test in which they had to discriminate noise bursts presented from a loudspeaker located to the left from identical noise bursts presented from a loudspeaker located to the right of midline, and a "hemifield" test in which both loudspeakers were located in their right hemifield. 2. Both of the tests were administered by the use of two different behavioral tasks: a conditioned-avoidance task in which the animals were trained to make or break contact with a water spout to indicate the location of a sound source, and a two-choice task that required the animals to walk to the source of the sound. 3. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were able to perform the midline discrimination although their localization acuity was reduced. However, the animals had great difficulty in learning to walk to the source of a sound in spite of the fact that they had received previous sound-localization training in the conditioned-avoidance task. This difficulty suggested that the monkeys no longer associated the sound with a location in space. 4. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were unable to discriminate the locus of a sound source when both loudspeakers were located in the same hemifield. 5. Bilateral ablation of auditory cortex results in both sensory and perceptual deficits. The presence of sensory deficits is indicated by the decreased acuity in the left-right discrimination and the inability to discriminate between two loudspeakers located in the same hemifield. The deficit in the perception of the locus of sound is indicated by the difficulty in learning to approach the source of a sound, an ability which normal monkeys exhibit without training. 6. There appear to be species' differences in the effect of auditory cortex lesions on sound localization. Although cortical lesions result in a sound-localization deficit in several species of primates and carnivores, they have little or no effect on rats.

Music Perception and Cognition Following Bilateral Lesions of Auditory Cortex

We present experimental and anatomical data from a case study of impaired auditory perception following bilateral hemispheric strokes. To consider the cortical representation of sensory, perceptual, and cognitive functions mediating tonal information processing in music, pure tone sensation thresholds, spectral intonation judgments, and the associative priming of spectral intonation judgments by harmonic context were examined, and lesion localization was analyzed quantitatively using straight-line two-dimensional maps of the cortical surface reconstructed from magnetic resonance images. Despite normal pure tone sensation thresholds at 250-8000 Hz, the perception of tonal spectra was severely impaired, such that harmonic structures (major triads) were almost uniformly judged to sound dissonant; yet, the associative priming of spectral intonation judgments by harmonic context was preserved, indicating that cognitive representations of tonal hierarchies in music remained intact and accessible. Brainprints demonstrated complete bilateral lesions of the transverse gyri of Heschl and partial lesions of the right and left superior temporal gyri involving 98 and 20% of their surface areas, respectively. In the right hemisphere, there was partial sparing of the planum temporale, temporoparietal junction, and inferior parietal cortex. In the left hemisphere, all of the superior temporal region anterior to the transverse gyrus and parts of the planum temporale, temporoparietal junction, inferior parietal cortex, and insula were spared. These observations suggest that (1) sensory, perceptual, and cognitive functions mediating tonal information processing in music are neurologically dissociable; (2) complete bilateral lesions of primary auditory cortex combined with partial bilateral lesions of auditory association cortex chronically impair tonal consonance perception; (3) cognitive functions that hierarchically structure pitch information and generate harmonic expectancies during music perception do not rely on the integrity of primary auditory cortex; and (4) musical priming may be mediated by broadly tuned subcomponents of the thala-mocortical auditory system.

Effect of bilateral auditory cortex lesions on absolute thresholds in Japanese macaques

1. The behavioral audiograms of four Japanese macaques (Macaca fuscata) were assessed before and after receiving two-stage bilateral lesions of auditory cortex. Thresholds were assessed for each ear with the use of insertion earphones. 2. The bilateral lesions resulted in a large initial hearing loss followed by partial recovery that left the animals with a permanent hearing loss in both ears. 3. The initial hearing loss consisted of a total insensitivity to sound in the ear contralateral to the second lesion with limited hearing in the other ear. However, the animal with the most complete lesion was initially unable to hear sound in either ear. Broadband noise was often more effective in eliciting a behavioral response than tones. 4. Partial recovery occurred in all animals and was observed as early as the first week after surgery. Most of this recovery occurred during the first 3-7 wk after surgery. This rapid phase of recovery was sometimes followed by a more gradual phase although thresholds were still elevated after 94 wk. 5. The permanent hearing loss, which averaged from 30 to 44 dB, was not constant across frequency. Threshold shifts were smallest at 63 Hz and progressively increased with frequency to a maximum loss from 8 to 25 kHz with slightly less loss at 32 kHz. 6. Analysis of the psychophysical functions and threshold stability gave no indication of any nonsensory deficits in attention or vigilance. 7. These results, taken with those of previous experiments, indicate that each hemisphere is primarily involved in the detection of sound in the contralateral ear and secondarily involved in detection in the ipsilateral ear. This arrangement differs from that seen in sound localization where each hemisphere is involved with the contralateral hemifield as opposed to the contralateral ear. Thus it appears that the functional organization of auditory cortex for sound localization is different from that for the detection and identification of sound itself.

Effect of unilateral and bilateral auditory cortex lesions on the discrimination of vocalizations by Japanese macaques

Ten Japanese macaques were trained to discriminate between two types of Japanese macaque coo vocalizations before and after auditory cortex ablation. Five of the animals were tested following left unilateral ablation, whereas the other five were tested following right unilateral ablation. After postoperative testing, symmetrical lesions were made in the remaining hemisphere in two animals from each group and the effect of bilateral lesions was assessed. The animals were tested using a shock avoidance procedure. Unilateral ablation of left auditory cortex consistently resulted in an initial impairment in the ability to discriminate between the vocalizations with the animals regaining normal performance in 5-15 sessions. In contrast, right unilateral ablation had no detectable effect on the discrimination. Bilateral auditory cortex ablation rendered the animals permanently unable to discriminate between the coos. Although the monkeys could learn to discriminate the coos from noise and from 2- and 4-kHz tones, they had great difficulty in discriminating between the coos and tones in the same frequency range as the coos (i.e., 500 Hz and 1 kHz). The initial impairment following left unilateral lesions indicates that the ability to perceive species-specific vocalizations is lateralized to the left hemisphere. The observation that bilateral lesions abolish the discrimination indicates that the recovery in the left lesion cases was the result of the right hemisphere mediating the discrimination.

Effect of auditory cortex ablation on localization and discrimination of brief sounds.

1. Dogs with bilateral auditory cortex lesions were tested on their ability to localize and discriminate brief sounds. In each test the animals were required to approach one of two goal boxes in order to indicate their response. 2. The results showed: a) that the operated animals could not solve the localization tasks when the goal boxes were located more than 125 cm away, but could solve the task if the goal boxes were located closer to the animal; b) that the operated animals could successfully discriminate brief bursts of click trains (i.e., 100/s versus 10/s, 0.3 s duration) even when required to indicate their discrimination by moving to goal boxes located 250 cm away, in spite of the fact that they could not successfully localize these sounds under similar conditions; c) that the operated animals tracked the source of a continuous sound instead of localizing it in a normal manner. 3. It appears that the deficit in sound localization resulting from cortical ablation is not due to any impairment in auditory attention or memory. Furthermore, the deficit cannot be ascribed to an inability to make a spatial response to an auditory cue. Instead, the deficit may be the result of a disconnection of the sound-localization mechanism from the motor mechanism necessary for some, though not all, behavioral responses.

Effects of bilateral auditory cortex ablation on behavior and unit activity in rat inferior colliculus during differential conditioning.

ArticlesEffects of bilateral auditory cortex ablation on behavior and unit activity in rat inferior colliculus during differential conditioningD. Birt, R. Nienhuis, and J. OldsD. Birt, R. Nienhuis, and J. OldsPublished Online:01 May 1978https://doi.org/10.1152/jn.1978.41.3.705MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited BySingle electrode micro-stimulation of rat auditory cortex: an evaluation of behavioral performanceHearing Research, Vol. 179, No. 1-2Globus pallidus lesions depress the excitatory responses to apomorphine but not amphetamine in the subthalamic nucleus of the behaving rat with a 6-OHDA nigra lesionBrain Research, Vol. 812, No. 1-2Effects of bilateral lesions of auditory cortex in mice on the acoustic startle responsePhysiology & Behavior, Vol. 54, No. 6Neural substrates for tone-conditioned bradycardia demonstrated with 2-deoxyglucose. I. Activation of auditory nucleiBehavioural Brain Research, Vol. 14, No. 3Functional activation in the auditory system of the rat produced by arousing reticular stimulation: a 2-deoxyglucose studyBrain Research, Vol. 299, No. 2Separation of associative from non-associative short latency changes in medial geniculate and inferior colliculus during differential conditioning and reversal in ratsBrain Research, Vol. 167, No. 1 More from this issue > Volume 41Issue 3May 1978Pages 705-715 Copyright & PermissionsCopyright © 1978 the American Physiological Societyhttps://doi.org/10.1152/jn.1978.41.3.705PubMed660230History Published online 1 May 1978 Published in print 1 May 1978 Metrics

Auditory cortex lesions and discrimination of spatial location by the rat

Five normal rats and four rats with bilateral lesions of auditory cortex were tested by the conditioned suppression procedure to determine their abilities to discriminate between spatially separated sound sources. The discrimination involved detection of a change in location of a train of clicks from a speaker on the animals' left to a speaker on the right. The separation between speakers was varied from 180° to 90°, 45°, 22°, 12°, 6°, and psychophysical functions were obtained using a method of descending limits. Both normal and brain-damaged animals were capable of discriminating left from right clicks and psychophysical curves were similar for the two groups. Histological analysis indicated that the lesions in each of the four brain-damaged rats destroyed primary auditory cortex as well as surrounding belt areas. Therefore, for the rat, auditory cortex was not found to be essential for discrimination of the spatial locations of auditory stimuli. The results are discussed in light of impairments in sound localization following lesions of auditory cortex in other mammalian species.

Effect of auditory neocortex ablation on identification of click rates in cats

Six experimental and 3 unoperated cats were trained with a go, no-go shock avoidance procedure to discriminate increases from decreases in the rate of presentation of all auditory cortex between the suprasylvian sulcus and rhinal fissure while 3 cats had bilateral auditory cortex lesions plus ablation of the cortex of the anterior lateral and anterior and middle suprasylvian gyri. A sixth 'naive' experimental cat received the present tests only after recovery from a bilateral auditory cortex ablation. After bilateral lesions, 5 of the experimental cats unexpectedly made no errors on no-go trials during retraining. This contrasts with their preoperative performance, as well as the performance of the 3 unoperated and the 'naive' operated cat, in which training was required for the successful discrimination of the two types of trials. This suggests that the neocortex may be more critical for mediating active 'go' responses to auditory stimuli than in preserving a memory for the difference between go and no-go stimuli. Further testing revealed that the thresholds of the operated cats did not differ from normal cats. All cats discriminated rates of 4/sec versus 6/sec clicks both with and without a neutral 5/sec background at levels significantly above chance.