ORGANIZATION OF AUDITORY, SOMATIC SENSORY, AND VISUAL PROJECTION TO ASSOCIATION FIELDS OF CEREBRAL CORTEX IN THE CAT

Cortical high-frequency oscillations (≈ 110 Hz) in cats are state-dependent and enhanced by a subanesthetic dose of ketamine

Ketamine is an NMDA receptor antagonist that has antidepressant and anesthetic properties. At subanesthetic doses, ketamine induces transient psychosis in humans, and is used to model psychosis in experimental animals. In rodents, subanesthetic doses of ketamine increase the power of high-frequency oscillations (HFO, > 100 Hz) in the electroencephalogram (EEG), a frequency band linked to cognitive functions. However, to date, the effects of ketamine in carnivores and primates have been poorly investigated. Here, we examined in the cat, cortical HFO during wakefulness, sleep, and after administering a sub-anesthetic dose of ketamine. Four cats were prepared with cortical electrodes for chronic polysomnographic recordings in head-restrained conditions. The cortical HFO power, connectivity, direction of the information flow using Granger Causality (GC) analysis, their relationships with respiratory activity, and the effect of auditory stimulation were analyzed. During wakefulness, but not during sleep, we found that HFO were coupled with the inspiratory phase of the respiration. After ketamine administration, HFO power was enhanced and remained associated with the inspiratory phase. GC analysis suggests that ketamine-enhanced HFO originate from the olfactory bulb (OB) and stream towards the prefrontal cortex (Pf). Accordingly, occluding the nostrils significantly reduced the power of the ketamine-enhanced HFO in both the OB and Pf. Finally, auditory stimulation did not affect HFO. In conclusion, the HFO are associated with respiration during wakefulness, but not during sleep. The enhancement of this rhythm by ketamine may disrupt cortical information processing, which could contribute to some of the neuropsychiatric effects associated with ketamine.

A combined approach for improving humanoid robots autonomous cognitive capabilities

Recent technologies advancements promise to change our lives dramatically in the near future. A new different living society is progressively emerging, witnessed from the conception of novel digital ecosystems, where humans are expected to share their own spaces and habits with machines. Humanoid robots are more and more being developed and provided with enriched functionalities; however, they are still lacking in many ways. One important goal in this sense is to enrich their cognitive capabilities, to make them more “intelligent” in order to better support humans in both daily and special activities. The goal of this research is to set a step in bridging the gap between symbolic AI and connectionist approaches in the context of knowledge acquisition and conceptualization. Hence, we present a combined approach based on semantics and machine learning techniques for improving robots cognitive capabilities. This is part of a wider framework that covers several aspects of knowledge management, from representation and conceptualization, to acquisition, sharing and interaction with humans. Our focus in this work is in particular on the development and implementation of techniques for knowledge acquisition. Such techniques are discussed and validated through experiments, carried out on a real robotic platform, showing the effectiveness of our approach. The results obtained confirmed that the combination of the approaches gives superior performance with respect to when they are considered individually.

Neurosurgery in feline epilepsy, including clinicopathology of feline epilepsy syndromes

Feline epilepsy is treated with antiseizure medications, which achieves fair to good seizure control. However, a small subset of feline patients with drug-resistant epilepsy requires alternative therapies. Furthermore, approximately 50 % of cats with epileptic seizures are diagnosed with structural epilepsy with or without hippocampal abnormality and may respond to surgical intervention. The presence of hippocampal pathology and intracranial tumors is a key point to consider for surgical treatment. This review describes feline epilepsy syndrome and epilepsy-related pathology, and discusses the indications for and availability of neurosurgery, including lesionectomy, temporal lobectomy with hippocampectomy, and corpus callosotomy, for cats with different epilepsy types.

Lack of a coherent theory limits the diagnostic and prognostic value of the (central) auditory processing disorder: a theoretical and clinical perspective

PURPOSE OF REVIEW

To consider pertinent issues towards developing a coherent theory of the auditory processing disorder (APD). By identifying the conceptual and methodological shortcomings that have thwarted development in this area for decades, we propose solutions to achieve a veridical endpoint to advance the field.

RECENT FINDINGS

Concerted efforts in the theoretical, experimental, and clinical domains have focused on validating the APD by demonstrating the " modality specificity " of the deficit. The importance of this conceptual framework is the delineation of auditory-perceptual dysfunctions from more generalized " supra modal" deficits, like those related to attention, memory, and language. Because contemporary schemata have limited the assessment of APD to auditory tasks alone ( unimodal testing), functional dissociations cannot be established, indeterminate diagnoses are problematic, and progress remains unduly constrained. The use of matched tasks in multiple sensory modalities is advocated as a diagnostic imperative to remedy this deficiency.

SUMMARY

Themes covered by this review include the need to develop a coherent theory of APD, to identify and limit factors which confound a valid diagnosis, and to validate the diagnosis by demonstrating the " modality specificity " of the deficit. Without an obligatory theoretical designation, the APD will remain as an obscure and controversial entity, limited to indeterminate test results and misdiagnoses.

Coherent neocortical 40-Hz oscillations are not present during REM sleep

During cognitive processes there are extensive interactions between various regions of the cerebral cortex. Oscillations in the gamma frequency band (≈40 Hz) of the electroencephalogram (EEG) are involved in the binding of spatially separated but temporally correlated neural events, which results in a unified perceptual experience. The extent of these interactions can be examined by means of a mathematical algorithm called 'coherence', which reflects the 'strength' of functional interactions between cortical areas. The present study was conducted to analyse EEG coherence in the gamma frequency band of the cat during alert wakefulness (AW), quiet wakefulness (QW), non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Cats were implanted with electrodes in the frontal, parietal and occipital cortices to monitor EEG activity. Coherence values within the gamma frequency (30-100 Hz) from pairs of EEG recordings were analysed. A large increase in coherence occurred between all cortical regions in the 30-45 Hz frequency band during AW compared with the other behavioral states. As the animal transitioned from AW to QW and from QW to NREM sleep, coherence decreased to a moderate level. Remarkably, there was practically no EEG coherence in the entire gamma band spectrum (30-100 Hz) during REM sleep. We conclude that functional interactions between cortical areas are radically different during sleep compared with wakefulness. The virtual absence of gamma frequency coherence during REM sleep may underlie the unique cognitive processing that occurs during dreams, which is principally a REM sleep-related phenomenon.

GABA-to-ACh ratio in basal forebrain and cerebral cortex varies significantly during sleep

STUDY OBJECTIVES

GABAergic and cholinergic transmission within the basal forebrain and cerebral cortex contribute to the regulation of sleep and wakefulness. In contrast to levels of acetylcholine (ACh), levels of endogenous GABA in basal forebrain and cortex during sleep and wakefulness have not previously been quantified. This study (1) tested the hypothesis that there are differential, state-specific changes in GABA levels within the substantia innominata (SI) region of the basal forebrain and somatosensory cortex; and (2) quantified the ratio of GABAergic to cholinergic transmission in the SI, cortex, and pontine reticular formation during rapid eye movement sleep (REM), non-REM sleep (NREM), and wakefulness.

DESIGN

Within/between subjects.

SETTING

University of Michigan.

PATIENTS OR PARTICIPANTS

Adult, male, purpose bred cats (n = 5).

INTERVENTIONS

In vivo microdialysis, high performance liquid chromatography, electrophysiological recordings.

MEASUREMENTS AND RESULTS

In the SI, GABA levels were significantly greater during NREM (17%) than during REM. In the cortex, GABA levels were significantly greater during NREM than during wakefulness (39%) and REM (63%). During prolonged wakefulness, there was a linear increase in cortical GABA levels, and the amount of time spent awake accounted for 87% of the variance in GABA. The GABA-to-ACh ratio was largest during NREM for all brain regions. REM was characterized by a 68% decrease in the GABA-to-ACh ratio across brain regions, always due to a decrease in GABA levels.

CONCLUSION

Three of the brain regions that comprise the anatomically distributed, sleep-generating network have in common a GABA-mediated, sleep-dependent decrease in the GABA-to-ACh ratio.

Multi- and unisensory decoding of words and nonwords result in differential brain responses in dyslexic and nondyslexic adults

The present functional magnetic resonance imaging (fMRI) study was designed, in order to investigate the neural substrates involved in the audiovisual processing of disyllabic German words and pseudowords. Twelve dyslexic and 13 nondyslexic adults performed a lexical decision task while stimuli were presented unimodally (either aurally or visually) or bimodally (audiovisually simultaneously). The behavioral data collected during the experiment evidenced more accurate processing for bimodally than for unimodally presented stimuli irrespective of group. Words were processed faster than pseudowords. Notably, no group differences have been found for either accuracy or for reaction times. With respect to brain responses, nondyslexic compared to dyslexic adults elicited stronger hemodynamic responses in the leftward supramarginal gyrus (SMG), as well as in the right hemispheric superior temporal sulcus (STS). Furthermore, dyslexic compared to nondyslexic adults showed reduced responses to only aurally presented signals and enhanced hemodynamic responses to audiovisual, as well as visual stimulation in the right anterior insula. Our behavioral results evidence that the two groups easily identified the two-syllabic proper nouns that we provided them with. Our fMRI results indicate that dyslexics show less neuronal involvement of heteromodal and extrasylvian regions, namely, the STS, SMG, and insula when decoding phonological information. We posit that dyslexic adults evidence deficient functioning of word processing, which could possibly be attributed to deficits in phoneme to grapheme mapping. This problem may be caused by impaired audiovisual processing in multimodal areas.

Chapter 6--motor planning of locomotor adaptations on the basis of vision: the role of the posterior parietal cortex

In this chapter, we consider the contribution of the posterior parietal cortex (PPC) to obstacle avoidance behavior and we define a model that identifies the major planning processes that are required for this task. A key aspect of this planning process is the need to integrate information concerning the obstacle, obtained from vision, together with an estimation of body and limb state. We suggest that the PPC makes a major contribution to this process during visually guided locomotion. We present evidence from lesion and single unit recording experiments in the cat that are compatible with this viewpoint.

Auditory influences on non-auditory cortices

Although responses to auditory stimuli have been extensively examined in the well-known regions of auditory cortex, there are numerous reports of acoustic sensitivity in cortical areas that are dominated by other sensory modalities. Whether in 'polysensory' cortex or in visual or somatosensory regions, auditory responses in non-auditory cortex have been described largely in terms of auditory processing. This review takes a different perspective that auditory responses in non-auditory cortex, either through multisensory subthreshold or bimodal processing, provide subtle but consistent expansion of the range of activity of the dominant modality within a given area. Thus, the features of these acoustic responses may have more to do with the subtle adjustment of response gain within a given non-auditory region than the encoding of their tonal properties.

The importance of modality specificity in diagnosing central auditory processing disorder

PURPOSE

This article argues for the use of modality specificity as a unifying framework by which to conceptualize and diagnose central auditory processing disorder (CAPD). The intent is to generate dialogue and critical discussion in this area of study.

METHOD

Research in the cognitive, behavioral, and neural sciences that relates to the concept of modality specificity was reviewed and synthesized.

RESULTS

Modality specificity has a long history as an organizing construct within a diverse collection of mainstream scientific disciplines. The principle of modality specificity was contrasted with the unimodal inclusive framework, which holds that auditory tests alone are sufficient to make the CAPD diagnosis. Evidence from a large body of data demonstrated that the unimodal framework was unable to delineate modality-specific processes from more generalized dysfunction; it lacked discriminant validity and resulted in an incomplete assessment. Consequently, any hypothetical model resulting from incomplete assessments or potential therapies that are based on indeterminate diagnoses are themselves questionable, and caution should be used in their application.

CONCLUSIONS

Improving specificity of diagnosis is an imperative core issue to the area of CAPD. Without specificity, the concept has little explanatory power. Because of serious flaws in concept and design, the unimodal inclusive framework should be abandoned in favor of a more valid approach that uses modality specificity.

Neonatal cortical ablation disrupts multisensory development in superior colliculus

The ability of cat superior colliculus (SC) neurons to synthesize information from different senses depends on influences from two areas of the cortex: the anterior ectosylvian sulcus (AES) and the rostral lateral suprasylvian sulcus (rLS). Reversibly deactivating the inputs to the SC from either of these areas in normal adults severely compromises this ability and the SC-mediated behaviors that depend on it. In this study, we found that removal of these areas in neonatal animals precluded the normal development of multisensory SC processes. At maturity there was a substantial decrease in the incidence of multisensory neurons, and those multisensory neurons that did develop were highly abnormal. Their cross-modal receptive field register was severely compromised, as was their ability to integrate cross-modal stimuli. Apparently, despite the impressive plasticity of the neonatal brain, it cannot compensate for the early loss of these cortices. Surprisingly, however, neonatal removal of either AES or rLS had comparatively minor consequences on these properties. At maturity multisensory SC neurons were quite common: they developed the characteristic spatial register among their unisensory receptive fields and exhibited normal adult-like multisensory integration. These observations suggest that during early ontogeny, when the multisensory properties of SC neurons are being crafted, AES and rLS may have the ability to compensate for the loss of one another's cortico-collicular influences so that normal multisensory processes can develop in the SC.

Ultrastructural analysis of projections to the pulvinar nucleus of the cat. I: Middle suprasylvian gyrus (areas 5 and 7)

The mammalian pulvinar nucleus (PUL) establishes heavy interconnections with the parietal lobe, but the precise nature of these connections is only partially understood. To examine the distribution of corticopulvinar cells in the cat, we injected the PUL with retrograde tracers. Corticopulvinar cells were located in layers V and VI of a wide variety of cortical areas, with a major concentration of cells in area 7. To examine the morphology and distribution of corticopulvinar terminals, we injected cortical areas 5 or 7 with anterograde tracers. The majority of corticopulvinar axons were thin fibers (type I) with numerous diffuse small boutons. Thicker (type II) axons with fewer, larger boutons were also present. Boutons of type II axons formed clusters within restricted regions of the PUL. We examined corticopulvinar terminals labeled from area 7 at the ultrastructural level in tissue stained for gamma-aminobutyric acid (GABA). By correlating the size of the presynaptic and postsynaptic profiles, we were able to quantitatively divide the labeled terminals into two categories: small and large (RS and RL, respectively). The RS terminals predominantly innervated small-caliber non-GABAergic (thalamocortical cell) dendrites, whereas the RL terminals established complex synaptic arrangements with dendrites of both GABAergic interneurons and non-GABAergic cells. Interpretation of these results using Sherman and Guillery's recent theories of thalamic organization (Sherman and Guillery [1998] Proc Natl Acad Sci U S A 95:7121-7126) suggests that area 7 may both drive and modulate PUL activity.

Sound frequency representation in cat auditory cortex

Using the intrinsic signal optical recording technique, we reconstructed the two-dimensional pattern of stimulus-evoked neuronal activities in the auditory cortex of anesthetized and paralyzed cats. The average magnitude of intrinsic signal in response to a pure tone stimulus increased steadily as the sound pressure level increased. A detailed analysis demonstrated that the evoked signals at early frames were scaled by the sound pressure level, which in turn indicated the presence of a minimum level of sound pressure beyond which stimulus-related intrinsic signal can be generated. Intrinsic signals evoked significantly by pure tone stimuli of different frequencies were localized and arranged in an orderly manner in the middle ectosylvian gyrus, which indicates that the primary auditory field (AI) is tonotopically organized. The arrangement of optimal frequencies obtained from optical recordings of the same auditory cortex, which were conducted on different days, was highly reproducible. Furthermore, other auditory fields surrounding AI in the recorded area were allocated based on the observed tonotopicity. We also conducted unit recordings on the cats used for optical recording with the same set of acoustic stimuli. The gross feature of the arrangement of optimal frequencies determined by unit recordings agreed with the tonotopic arrangement determined by the optical recording, although the precise agreement was not obtained.

Audiovisual integration of letters in the human brain

Letters of the alphabet have auditory (phonemic) and visual (graphemic) qualities. To investigate the neural representations of such audiovisual objects, we recorded neuromagnetic cortical responses to auditorily, visually, and audiovisually presented single letters. The auditory and visual brain activations first converged around 225 ms after stimulus onset and then interacted predominantly in the right temporo-occipito-parietal junction (280345 ms) and the left (380-540 ms) and right (450-535 ms) superior temporal sulci. These multisensory brain areas, playing a role in audiovisual integration of phonemes and graphemes, participate in the neural network supporting the supramodal concept of a "letter." The dynamics of these functions bring new insight into the interplay between sensory and association cortices during object recognition.

Effect of spinal cord lesions on forelimb target-reaching and on visually guided switching of target-reaching in the cat

Cats were trained to reach to an illuminated tube placed horizontally at shoulder level and retrieve food with the forepaw. The trajectory of an infrared light emitting diode, taped to the wrist dorsum, was recorded with a SELSPOT-like recording system. Movement paths and velocity profiles were compared before and after lesions: (1) in dorsal C5, transecting cortico- and rubrospinal pathways to the forelimb segments so that the cats could only use the C3-C4 propriospinal neurones (PNs) to command reaching, (2) in the ventral part of the lateral funicle in C5, transecting the axons of C3-C4 PNs so that the cats had to use circuitry in the forelimb segments to command reaching. Comparison of trajectories and velocity profiles before and after lesion 1 did not reveal any major qualitative change. After lesion 2, the last third of the movement was fragmented with separate lifting and protraction. Switching of target-reaching occurred when illumination was shifted to another tube during the ongoing movement. The switching latency measured from the time of illumination shift to the earliest change in movement trajectory had a minimal value of 50-60 ms. Short latencies were present after lesion 1 as well as lesion 2 which suggest that fast switching mediated by the C3-C4 PNs and the interneuronal system in the forelimb segments is controlled in parallel by the brain. In order to test a hypothesis that fast switching depends on the tectospinal and tecto-reticulospinal pathways (the tecto-reticulo-spinal system) a ventral lesion was made in C2 aiming at interrupting these pathways. Large ventral C2 lesions tended to block conduction in the more dorsally located rubrospinal (less in corticospinal) axons probably due to compression during surgery. When conduction in the rubrospinal tract was completely interrupted by a ventral C2 lesion which also completely transected the axons of the tecto-reticulo-spinal system, then there was a prolongation of the switching latency with 10-20 ms. After a similar large ventral lesion with remaining conduction in the rubrospinal tract the switching latencies were unchanged. It is postulated that fast visually governed switching does not depend on the tecto-reticulo-spinal system alone but on more dorsally located pathways, presumably the rubrospinal tract, either acting alone or together with the tecto-reticulo-spinal system. It is further postulated that the delayed switching after interruption of conduction both in the rubrospinal tract and the tecto-reticulo-spinal system depends on the corticospinal tract. Visual control of rubrospinal and of corticospinal neurones is considered. It is postulated that target-reaching normally depends on signals in the cortico- and rubrospinal tracts and mechanisms for co-ordination of activity in them as required during switching is discussed in view of the findings now reported.

Patterns of inputs to the parietal cortex efferent neurons from the motor cortex and cerebellum in the cat

Responses of parietal association cortex efferent neurons to motor cortex and cerebellar nuclei stimulation were studied intracellularly in anaesthetized cats. Efferent neurons of the parietal cortex were identified according to their antidromic activation on stimulation of the motor cortex, pontine nuclei proper and red nucleus. Monosynaptic excitatory postsynaptic potentials of ipsilateral anterior suprasylvian and lateral gyri neurons to motor cortex stimulation have been established. Oligo- and polysynaptic excitatory responses of parietal cortex efferent neurons to cerebellar nuclei stimulation have been recorded. Correlation between the latencies of cerebellar-induced excitatory postsynaptic potentials and antidromic invasion of neurons on stimulation of different parietal cortex efferent projections (corticocortical, corticopontine, corticorubral) has been obtained. A similar correlation has been found between the latencies of excitatory postsynaptic potentials evoked on stimulation of one of the cerebellar nuclei and latencies of antidromic invasion induced on stimulation of all studied parietal cortex efferent systems. Feedforward and feedback mechanisms in the input-output organization of parietal association cortex have been discussed.

Modality Specificity as a Criterion for Diagnosing Central Auditory Processing Disorders

A central "auditory" processing disorder (CAPD) is an auditory perceptual dysfunction that cannot be explained on the basis of peripheral hearing loss. As a concept, CAPD has not been completely validated, and many issues continue to be controversial. A primary issue of concern is whether currently used tests to evaluate CAPD are sensitive to factors that are not of an auditory perceptual nature. In this paper, we consider the case for modality specificity as a criterion for improving the specificity of diagnosing CAPD. Demonstrating the modality-specific nature of sensory processing deficits is one way to rule out nonperceptual factors as explanations for observed dysfunction.

Retrograde axonal transport of different fluorescent tracers from the neocortex to the suprageniculate nucleus in the rat

The retrograde fluorescent tracers in a combination of two different dyes (Fluoro gold/Nuclear yellow or Fast blue/Fluoro gold) were used for the study of the projections from the medial geniculate body to the frontal and temporal cortices in rats. There were only single-labeled cells, no double-labeled ones in the medial geniculate body (MGB). The suprageniculate nucleus (SG) was considered to be the origin of the rat direct pathway to the frontal cortex. The present results suggest that projections from the suprageniculate nucleus to the frontal cortex and the temporal cortex consist of separate neuronal groups in the rat MGB and SG. The inputs to the SG from the auditory and oculomotor system may be processed in different ways.

The spatiotemporal organization of auditory, visual, and auditory-visual evoked potentials in rat cortex

Four placements of an 8 x 8 channel microelectrode array were used to map auditory, visual, and combined auditory-visual evoked potentials (AEP, VEP, AVEP) from a total of 256 electrode sites over a 7 x 7 mm2 area including most of somatosensory, auditory, and visual cortex in the right hemisphere of the rat. The unimodal AEP and VEP consisted of an archetypal response sequence representing a systematic spatial and temporal activation of primary and secondary sensory cortex. Spatiotemporal analysis of these waveforms indicated that they could be decomposed into a small number of spatial and temporal components; components that are related to patterns of specific and non-specific thalamocortical projections connecting the auditory and visual nuclei of the thalamus with primary and secondary auditory and visual cortex. These data suggest that the AEP and VEP complex are the cortical reflection of asynchronous activation of parallel thalamocortical projection systems. The areal distribution of the AEP and VEP also overlapped, primarily in secondary auditory and visual cortex, indicating that these regions contain populations of cells responding to either modality. Polymodal auditory-visual stimulation resulted in unique activation of two isolated populations of neurons positioned in secondary auditory and secondary visual cortex which were revealed by difference waveforms, computed by subtracting the sum of the AEP and VEP from the AVEP complex. Retrograde labeling of the polymodal zones indicated that they receive parallel thalamocortical projections primarily from non-specific auditory and visual thalamic nuclei including the medial and dorsal divisions of the medial geniculate nucleus (MGm and MGd), the suprageniculate nucleus (SGN), and the lateral posterior nucleus (LP). The polymodal zone in visual cortex also receives specific projections from the dorsal division of the lateral geniculate nucleus (LGd). These data conform to a general model of thalamocortical organization in which specific thalamic nuclei with a high degree of modality specificity make restricted projections to primary sensory cortex and parts of secondary sensory cortex, and association thalamic nuclei with a high degree of sensory convergence make more divergent cortical projections. Primary and secondary sensory cortex, as well as distinct zones of polysensory cortex appear to be activated in tandem via parallel thalamocortical projections. Thus, the cerebral cortex must have simultaneous access to both unimodal and polymodal sensory information.

The mode of cerebellar activation of pyramidal neurons in the cat parietal cortex (areas 5 and 7): an intracellular HRP study

Response properties of 180 pyramidal neurons (11 layer II, 66 layer III, 7 layer IV, 76 layer V and 20 layer VI neurons) in the cat parietal cortex (areas 5 and 7) were examined intracellularly with stimulations of the cerebellar nucleus (CN), the thalamic ventroanterior nucleus (VA) and the lateral posterior nucleus (LP) under pentobarbital anesthesia. Pyramidal neurons were identified morphologically or electrophysiologically with antidromic responses by pontine nuclei (PN) stimulation. CN and VA stimulations evoked EPSPs in layer II, III, V and VI pyramidal neurons, but scarcely induced EPSPs in layer IV pyramidal ones. The mean latencies of CN-EPSPs were nearly the same through layers II to V, giving values of around 4.5 ms, but that of layer VI pyramidal neurons was much longer (5.5 +/- 0.8 ms: mean +/- SD). Those of VA-EPSPs were also nearly the same through all layers (around 2.2-2.8 ms). In case of LP stimulation, EPSPs were scarcely recorded in layer II and IV pyramidal neurons. The mean latency of LP-EPSPs was much shorter in layer III (2.6 +/- 1.0 ms) than those in layers V and VI (3.8-3.9 ms). It was noted that pyramidal neurons in layers II and III responded more frequently to CN and VA stimulations than those in deeper layers, and that the amplitudes of CN- and VA-EPSPs were large and conspicuous in layer III. In layer V, a statistical difference in the latency distributions of CN-, VA-, and LP-EPSPs between fast- and slow-type pyramidal neurons was not detected. The present results suggest that there exist the different modes of thalamocortical (T-C) innervations in the cat parietal cortex; the superficial T-C innervation of CN-VA inputs and the deep T-C innervation of LP inputs.

Visual and auditory cortical lesions following acquisition of an intensity discrimination in rats fail to disrupt cross-modal transfer

The effect of visual or auditory decortication on cross-modal transfer of an intensity discrimination was examined in rats. Twenty animals were first trained under either visual-auditory (V-A) or auditory-visual (A-V) cross-modal transfer (CMT) in a shuttlebox using a shock avoidance pardigm. Prior to the second training session, five of the A-V animals received auditory ablations and five V-A animals received visual ablations. The other 10 animals served as controls and received sham operations. The results reveal that CMT occurred in both experimental groups following cortical ablations. It is possible that information regarding stimulus intensity was transferred from a cortical region used during the original training session to the cortex used in the second or retraining session, prior to surgery. Alternatively, it may be that some subcortical structure (e.g. the amygdala, superior colliculus, or reticular formation) may be involved in CMT of intensity.

The auditory cortex of the mouse: connections of the ultrasonic field

The cortical and subcortical connections of the ultrasonic field (UF) of the auditory cortex of the house mouse (Mus musculus) were studied by using retrograde and anterograde transport of horseradish peroxidase (HRP). Small amounts of HRP were locally injected into the electrophysiologically defined UF. Superficial (layer I-IV) and deep (layer IV-VI) injections were prepared. Superficial injections led to labelling of both cells (retrograde) and terminals (anterograde) in areas of the ipsilateral primary and secondary auditory cortex and in its dorsoposterior field, in an ipsilateral dorsal association area (patches of label), probably in ipsilateral secondary somatosensory cortex, in the contralateral homotopic UF, and in the ipsilateral medial geniculate body (MGBv, MGBd, and MGBm) and caudal posterior nucleus complex. Deep injections showed the same connectivities as superficial ones and, in addition, terminals in the very caudal caudatoputamen, in the nucleus limitans and the nucleus reticularis of the thalamus, in the rostral pole, the dorsomedial, and lateral nucleus of the inferior colliculus, in the stratum griseum intermediale of the superior colliculus, and in a pontine nucleus ventromedial of the lateral lemniscus. All these projections occurred only ipsilaterally. The majority of connections, except those with the nucleus limitans, superior colliculus and pontine nucleus, suggest that UF is part of the primary anditory cortex (AI) and/or of the anterior anditory field (AAF) of the auditory cortex. Since UF has no regular tonotopy, this has important implications for the functional role that AI/AAF can have in communication-sound analysis.

Long-latency auditory-evoked potentials: role of polysensory association cortex in the cat

The objective of this study has been to define the role of polysensory association cortex in the generation of "wave NA" and of "wave C," long-latency auditory-evoked potentials recorded from the vertex of conscious cats as, respectively, a marked negative potential of latency 30-48 msec followed by a broad positive wave of latency 50-75 msec. Wave C may represent the feline analogue of the longer latency human auditory-evoked potential wave P2, insofar as both waveforms are very large amplitude, long duration positivities characterized by long recovery cycles. Based on previous studies of wave C and the generators of other middle-latency evoked potentials, we hypothesized that both wave NA and wave C might reflect, at least in part, the cortical culmination of a nonlemniscal line auditory association system arising in reticulothalamic projections to intralaminar and associated ventral thalamic regions. Relays from these thalamic areas are known to project to polysensory association cortex, including pericruciate gyrus, anterolateral gyrus, and medial suprasylvian gyrus. Therefore we implemented a series of lesion experiments to characterize the role of each of these cortical areas in the production of wave NA and wave C. Our results indicate that all three polysensory association areas contribute significantly to both waves NA and C, although the largest effects followed ablation of the pericruciate area alone. Thus, the generator substrates of waves NA and C appear to involve a long-recovery cycle system which functionally incorporates activation of association cortex.

Seeing speech: visual information from lip movements modifies activity in the human auditory cortex

Neuromagnetic responses were recorded over the left hemisphere to find out in which cortical area the heard and seen speech are integrated. Auditory stimuli were Finnish/pa/syllables presented together with a videotaped face articulating either the concordant syllable/pa/(84% of stimuli, V = A) or the discordant syllable/ka/(16%, V not equal to A). In some subjects the probabilities were reversed. The subjects heard V not equal to A stimuli as/ta/ or ka. The magnetic responses to infrequent perceptions elicited a specific waveform which could be explained by activity in the supratemporal auditory cortex. The results show that visual information from articulatory movements has an entry into the auditory cortex.

Topographic analysis of field potentials in rat vibrissa/barrel cortex

An 8 x 8 multichannel microelectrode array was used to simultaneously record epicortical field potentials, evoked by displacement of contralateral vibrissae, from a 4 x 4 mm2 area of vibrissa/barrel cortex in 4 rats. The epicortical responses began with early positive (P1) and negative (N1) sharp waves, followed by slower positive (P2) and negative (N2) waves. The potential complex systematically shifted location with vibrissa stimulated, in accordance with the known somatotopic anatomy of vibrissa/barrel cortex. Topographical distributions of potentials at the P1, N1, P2 and N2 peaks were approximately concentric, but had distinct spatial extents, suggesting that they were generated by different but overlapping neuronal subpopulations. We propose that the SEP in the vibrissa/barrel cortex is produced by both sequential and parallel processing of somatosensory information, and that all components of the epicortical SEP are generated only in primary somatosensory cortex of the rat. Applications and weaknesses of topographic analysis methods are discussed.

Visuotopic organization of the lateral suprasylvian area and of an adjacent area of the ectosylvian gyrus of cat cortex: a physiological and connectional study

We have explored the visuotopic organization of the territory surrounding the middle suprasylvian sulcus (MSS) of cat cerebral cortex by electrophysiological mapping, and by tracing the topography of its cortical and subcortical connections using wheatgerm-agglutinin horseradish peroxidase (WGA-HRP). Observations from the two approaches were concordant, and confirmed the presence of two separate visual areas in the MSS that approximate, but do not exactly correspond, to the location and internal organization of the posterior medial and posterior lateral lateral suprasylvian (PMLS, PLLS) areas of Palmer et al. (1978). We define as part of the lateral suprasylvian (LS) area the territory on the medial bank and caudal end of the lateral bank of the MSS that receives a topographically organized projection from the region of area 17 representing the lower visual quadrant. This territory is connected with other structures that are themselves striate-recipient (cortical areas 18 and 19, and the lateral division of the lateral posterior (LPl) nucleus), and with a variety of nuclei that receive direct retinal input, such as the C-laminae of the LGd, the medial interlaminar nucleus (MIN), and the superficial layers of the superior colliculus (SC). Its connections with the LPl, LGd, MIN, and SC correspond topographically with the input from area 17. Revised maps of area LS were produced from the physiological and connectional data: its rostral border is formed by a representation of lower visual elevations with the horizontal meridian represented caudally, and its lateral border is formed by the vertical meridian; area LS shares a representation of the center of gaze with the visual area of the lateral bank at its caudal end. The adjacent lateral bank area has larger receptive fields than area LS, and very different connectivity. It receives no input from area 17 and little input from striate-recipient structures, including area LS, but instead is connected to more remote extrastriate visual areas, such as the anterior ectosylvian visual (AEV) area in insular cortex, and to zones of the thalamus in receipt of tectal input (LPm and the lateromedial-suprageniculate nuclear complex). According to both mapping approaches, the lateral bank area contains representations of both the upper and lower visual quadrants but a rather limited degree of visuotopic order. We refer to it as the posterior ectosylvian visual (PEV) area, because it appears to be functionally and connectionally dissociated from area LS, but is possibly a functional antecedent of area AEV.

Association brain systems as apparatus of behavior control involving dominanta and conditioning

The author's major conception concerning the associative brain systems (thalamoparietal and thalamofrontal) as the behavior control system are presented. The participation of association systems in performance of higher brain functions, due to the entrance of the whole information spectrum of biological and signal significance and the presence of neuronal plastic mechanisms, ensures the mechanism for retrieving the whole behavior programs from long-term memory, the ability of short-term storing of behavior programs, and estimation of their adequacy on the ground of dominanta and conditioning mechanisms.

Parietal projection of thalamocortical fibers from the ventroanterior-ventrolateral complex of the cat thalamus

Anterograde labelling following focal injections of Phaseolus vulgaris leucoagglutinin was used to identify the parietal distribution of thalamocortical (TC) fibers from the ventroanterior-ventrolateral (VA-VL) complex of the cat thalamus. In injections in the ventrolateral or the caudal part of the VA-VL complex, labelled TC fibers were distributed in layers I, III and IV of the parietal areas 5a and/or 5b, whereas in injections located more rostrally or dorsomedially, labelled TC fibers were almost confined to layer I.

Cat-P300 present after association cortex ablation

The cat-P300 is a positive endogenous potential, larger to a stimulus when rare than when frequent, with a latency of 200-500 msec. The role of polysensory association cortex, postulated to be important in human P300 generation, was assessed in the cat. EEG was recorded in 13 awake cats from a skull screw at the vertex. Stimuli included frequent (P = 0.80) 1 kHz and rare (P = 0.10) 2 kHz tone pulses with probabilities counterbalanced across 260-trial blocks. After 12 preoperative sessions, bilateral ablations were made of pericruciate cortex (4 cats), anterior lateral and medial suprasylvian gyri (4 cats) and all 3 areas (5 cats). Postoperatively, all 13 cats showed a P300 across 12 recording sessions. Thus polysensory association cortex is not essential for generation of the cat-P300.

Functional organization of interzonal transcallosal connections in the sensorimotor cortex

Transcallosal evoked potentials (EP) in cat sensorimotor cortex, arising in response to stimulation of the visual or auditory zone of an opposite hemisphere, were investigated. Interzonal transcallosal responses (TCR) were shown to be present along the entire surface of the sensorimotor cortex. Videomotor EPs were mainly in the form of responses with initial negativity. The latent periods of audiomotor EPs were longer than those of videomotor EPs. Negative-positive videomotor responses had greater amplitudes as compared to the amplitudes of synphasic or audiomotor EPs. Responses with initial positivity, on the contrary, had greater amplitudes during Field AI stimulation than they had during the stimulation of Field 19. Interzonal transcallosal responses in MI zone were characterized by interhemispheric asymmetry. In a per-pair comparison of the amplitudes of response components, individual asymmetry was revealed for videomotor EPs. Audiomotor responses in the majority of investigated animals were of greater magnitude in the left hemisphere. The left hemisphere dominance for audiomotor EPs was mainly observed in females, whereas in males the asymmetry revealed was individual. It is suggested that the peculiarities of the interhemispheric asymmetry of interzonal audio- and videomotor functional transcallosal connections are determined by specificity of the intrazonal asymmetry of transcallosal streams in projection and association cortical areas.

Interhemispheric interzonal connections in the parietal cortex

In acute experiments on cats immobilized by tubarine transcallosal responses (TCRs) to the stimulation of the visual or auditory cortex of the opposite hemisphere were investigated in the parietal associative region. It was found that interzonal heterotopical TCRs could be recorded along the entire surface of the parietal cortex and were in two forms: positive-negative or negative-positive. Positive-negative evoked potentials (EPs) had greater latent periods. Negative-positive TCRs disappeared after the corpus callosum section or after the section of intracortical pathways on the side of recording and/or stimulation. EPs with initial positivity changed insignificantly as a result of these operations. Interzonal TCRs were characterized by the presence of interhemispheric asymmetry. The amplitude of early components in visual-parietal EPs of any configuration appeared to be greater in the right hemisphere. These responses also had a greater latent period. According to the magnitude of the late positive wave in visual-parietal TCRs the left hemisphere appeared to be dominant. Interhemispheric asymmetry in audioparietal EPs was individual. The amplitude of the early positive component prevailed as to magnitude in the right hemisphere in males and in the left hemisphere in females. The late negative wave in animals of either sex was greater in the right hemisphere. The peculiarities of generation and interhemispheric asymmetry of different components in visual-parietal and audioparietal TCRs are discussed. A symmetricising function of the parietal associative cortex is suggested.

Experimentally induced visual projections into auditory thalamus and cortex

Retinal cells have been induced to project into the medial geniculate nucleus, the principal auditory thalamic nucleus, in newborn ferrets by reduction of targets of retinal axons in one hemisphere and creation of alternative terminal space for these fibers in the auditory thalamus. Many cells in the medial geniculate nucleus are then visually driven, have large receptive fields, and receive input from retinal ganglion cells with small somata and slow conduction velocities. Visual cells with long conduction latencies and large contralateral receptive fields can also be recorded in primary auditory cortex. Some visual cells in auditory cortex are direction selective or have oriented receptive fields that resemble those of complex cells in primary visual cortex. Thus, functional visual projections can be routed into nonvisual structures in higher mammals, suggesting that the modality of a sensory thalamic nucleus or cortical area may be specified by its inputs during development.

Morphological features of layer V pyramidal neurons in the cat parietal cortex: an intracellular HRP study

Layer V pyramidal neurons in the cat parietal cortex (areas 5 and 7) were investigated with intracellular HRP staining. Antidromic responses were recorded intracellularly as well as extracellularly with pontine stimulation under Nembutal anesthesia. The relationship between the latency of antidromic responses and the morphology of HRP-stained neurons was analyzed. A total of 65 neurons were stained with HRP, and sixteen of these neurons were activated antidromically with pontine stimulation. Two distinct groups of layer V pyramidal neurons were detected morphologically by intracellular HRP staining; i.e., one (F type) consisted of neurons with relatively large somata (58.4 +/- 8.1 micron X 24.5 +/- 5.1 micron, N = 11) and aspiny or sparsely spinous apical dendrites, and the other (S type) consisted of neurons with smaller somata (44.6 +/- 7.6 micron X 19.3 +/- 3.9 micron, N = 22) and richly spinous apical dendrites. These two groups showed different electrophysiological properties; i.e., the former responded antidromically to pontine stimulation at a latency shorter than 1.5 ms (namely, with a conduction velocity faster than 18 m/second) and the latter responded at a latency longer than 1.5 ms. The two neuronal types in the parietal cortex corresponded respectively to fast and slow pyramidal tract neurons (PTNs) investigated in the sensorimotor cortex. Although their morphological features were almost similar to those of PTNs, the branching pattern of apical dendrites of the F-type pyramidal neuron seemed to be different from that of fast PTNs. In the parietal cortex, apical dendrites of F-type neurons showed rather frequent branching in layer I. This was similar to the pattern of branching in slow PTNs. Such a characteristic branching pattern suggested that, in the cat parietal cortex, layer V pyramidal neurons of both types are adapted to receive cerebellar inputs through the ventroanterior (VA) thalamic nucleus to the superficial cortical layers.

Cortical and subcortical afferent connections of a posterior division of feline area 7 (area 7p)

Area 7 of the cat, as identified cytoarchitecturally, includes cortex both on the middle suprasylvian gyrus and on the anterior lateral gyrus. The aim of the experiments reported here was to determine whether within this zone there are subdivisions with qualitatively different patterns of afferent connectivity. Deposits of distinguishable retrograde tracers were placed at 29 sites in and around area 7 of 15 cats; cortical and subcortical telencephalic structures were then scanned for retrograde labeling. Our results indicate that cortex on the anterior lateral gyrus, although often included in area 7, is indistinguishable on connectional grounds from adjacent somesthetic cortex (area 5b). Cortex with strong links to visual, oculomotor, and association areas is confined to the middle suprasylvian gyrus and the adjacent lateral bank of the lateral sulcus. We refer to this discrete, connectionally defined zone as posterior area 7 (area 7p). Area 7p receives input from visual areas 19, 20a, 20b, 21a, 21b, AMLS, ALLS, and PLLS; from frontal oculomotor cortex (areas 6m and 6l); and from cortical association areas (posterior cingulate cortex, the granular insula, the posterior ectosylvian gyrus, and posterior area 35). Thalamic projections to area 7p arise from three specific nuclei (pulvinar; nucleus lateralis intermedius, pars caudalis; nucleus ventralis anterior) and from the intralaminar complex (nuclei centralis lateralis, paracentralis and centralis medialis). Neurons in a division of the claustrum immediately beneath the somatosensory and visual zones project to area 7p. Within area 7p, anterior-posterior regional differentiation is present, as indicated by the spatial ordering of projections from cingulate and frontal cortex, the thalamus, and the claustrum. Area 7p, as delineated by connectional analysis in this study, resembles cortex of the primate inferior parietal lobule both in its location relative to other cortical districts and in its pattern of neural connectivity.

An extensive intrinsic association fiber system within cat area 7 revealed by anterograde and retrograde axon tracing methods

The associational connections within area 7 on the crown of the middle suprasylvian gyrus in adult cats were investigated with extracellular axon tracing techniques. Injections of wheat germ agglutinin conjugated to horseradish peroxidase or of 3H-proline into area 7 revealed the presence of widespread intrinsic connections that extend over the rostral to caudal extent of the middle suprasylvian gyrus (up to 10 mm in one direction from injection sites). The connections have a complex organization with cell bodies and particulate label concentrated in patches. The patches are irregular in shape and do not form any obvious pattern. Although the transported label is concentrated in patches, large numbers of retrogradely labeled cells and significant quantities of anterogradely transported label are found in the spaces between patches. The long associational connections originate from cells in layers 2-6 and project to all cortical layers. Pyramidal cells are the primary source of the projections.

Single unit activity in cat prefrontal and parietal cortex during performance of a symmetrically reinforced go-no go task

Relationships between the performance in a symmetrically reinforced go-no go task and cellular firing patterns in prefrontal and parietal association areas of the neocortex were studied in six cats. During recordings, animals lay in a box, with their heads fixed to a stereotaxic frame, and performed an auditory go-no go task by pressing a retractable lever in front of them. Units obtained were classified into eight types according to the correlation of their activity changes with aspects of the task and/or with sensory stimuli. These types were (poly-) sensory, reward related, EMG-related, EOG-related, event-related, movement-initiating, expressing expectancy or novelty, and nonspecific or task-unrelated active units. Between the two recording areas a considerable degree of similarity was obtained in unit firing patterns. It was concluded that within the cerebral cortex, and especially within its association areas, a considerable functional overlap exists, that neurons may be involved in the processing of several and rather different phenomena, and that the processing of information at this level of the brain is generally done via widespread, interwoven neuronal nets so that only the average network activity, but not that of a particular, single neuron, represents a stimulus or an event.