Corticostriatal connections of the superior temporal region in rhesus monkeys

Corticostriatal connections of auditory areas within the supratemporal plane and in rostral and caudal portions of the superior temporal gyrus were studied by the autoradiographic anterograde tracing technique. The results show that the primary auditory cortex has limited projections to the caudoventral putamen and to the tail of the caudate nucleus. In contrast, the second auditory area within the circular sulcus has connections to the rostral and the caudal putamen and to the body of the caudate nucleus and the tail. The association areas of the superior temporal gyrus collectively have widespread corticostriatal projections characterized by differential topographic distributions. The rostral part of the gyrus projects to ventral portions of the head of the caudate nucleus and of the body and to the tail. In addition, there are connections to rostroventral and caudoventral portions of the putamen. The mid-portion of the gyrus projects to similar striatal regions, but the connections to the head of the caudate nucleus are less extensive. Compared with the rostral and middle parts of the superior temporal gyrus, the caudal portion has little connectivity to the tail of the caudate nucleus. It projects more dorsally within the head and the body and also more dorsally within the caudal putamen. These differential patterns of corticostriatal connectivity are consistent with functional specialization at the cortical level.     

Dissociation of visual and auditory pattern discrimination functions within the cat's temporal cortex

In ablation-behavior experiments performed in adult cats, a double dissociation was demonstrated between ventral posterior suprasylvian cortex (vPS) and temporo-insular cortex (TI) lesions on complex visual and auditory tasks. Lesions of the vPS cortex resulted in deficits at visual pattern discrimination, but not at a difficult auditory discrimination. By contrast, TI lesions resulted in profound deficits at discriminating complex sounds, but not at discriminating visual patterns. This pattern of dissociation of deficits in cats parallels the dissociation of deficits after inferior temporal versus superior temporal lesions in monkeys and humans.     

Intensity coding of auditory stimuli: an fMRI study

The effect of stimulus intensity (sound pressure level, SPL) of auditory stimuli on the BOLD response in the auditory cortex was investigated in 14 young and healthy subjects, with no hearing abnormalities, using echo-planar, functional magnetic resonance imaging (fMRI) during a verbal and a non-verbal auditory discrimination task. The stimuli were presented block-wise at three different intensities: 95, 85 and 75 dB (SPL). All subjects showed fMRI signal increases in superior temporal gyrus (STG) covering primary and secondary auditory cortex. Most importantly, the spatial extent of the fMRI response in STG increased with increasing stimulus intensity. It is hypothesized that spreading of excitation is associated with the encoding of increasing stimulus intensity levels. In addition, we found bifrontal activation supposedly evoked by the auditory-articulary loop of working memory. The results presented here should assist in the design of optimal activation strategies for studying the auditory cortex with fMRI paradigms and may help in understanding intensity coding of auditory stimuli.     

Parallel processing in the auditory cortex of primates

Evidence from anatomical tracer studies as well as lesions of the primary auditory cortex (AI) indicate that the principal relay nucleus of the auditory thalamus, the ventral part of the medial geniculate (MGv), projects in parallel to AI and the rostral area on the supratemporal plane of the macaque monkey. The caudomedial area, by contrast, receives input from MGv only indirectly via AI, and neurons in this area are often tuned to the spatial location of a complex sound. The belt areas on the lateral surface of the superior temporal gyrus receive input from the primary areas. Neurons in these areas respond better to more complex stimuli, such as band-pass noise pulses of frequency-modulated sweeps, than to pure tones. Often neurons in the lateral belt respond well to species-specific communication calls. The hypothesis is put forward that the central auditory pathways in the macaque monkey are organized into parallel streams, similar to the visual system, one for the processing of spatial information, the other for the processing of auditory "patterns". Evidence from neuroimaging studies in humans with MRI and PET are consistent with this hypothesis. Virtual auditory space stimuli lead to selective activation of an inferior parietal region, whereas speech-like stimuli activate superior temporal regions.     

Subdivisions of auditory cortex and levels of processing in primates

In a series of experiments on New World and Old World monkeys, architectonic features of auditory cortex were related to tone frequency maps and patterns of connections to generate and evaluate theories of cortical organization. The results suggest that cortical processing of auditory information involves a number of functionally distinct fields that can be broadly grouped into four or more levels of processing. At the first level, there are three primary-like areas, each with a discrete pattern of tonotopic organization, koniocortical histological features, and direct inputs from the ventral division of the medial geniculate complex. These three core areas are interconnected and project to a narrow surrounding belt of perhaps seven areas which receive thalamic input from the major divisions of the medial geniculate complex, the suprageniculate/limitans complex, and the medial pulvinar. The belt areas connect with a lateral parabelt region of two or more fields that are almost devoid of direct connections with the core and the ventral division of the medial geniculate complex. The parabelt fields connect with more distant cortex in the superior temporal gyrus, superior temporal sulcus, and prefrontal cortex. The results indicate that auditory processing involves 15 or more cortical areas, each of which is interconnected with a number of other fields, especially adjoining fields of the same level.     

Inputs to a physiologically characterized region of the inferior colliculus of the young adult CBA mouse

Presbycusis is a sensory perceptual disorder involving loss of high-pitch hearing and reduced ability to process biologically relevant acoustic signals in noisy environments. The present investigation is part of an ongoing series of studies aimed at discerning the neural bases of presbycusis. The purpose of the present experiment was to delineate the inputs to a functionally characterized region of the dorsomedial inferior colliculus (IC, auditory midbrain) in young, adult CBA mice. Focal, iontophoretic injections of horseradish peroxidase were made in the 18-24 kHz region of dorsomedial IC of the CBA strain following physiological mapping experiments. Serial sections were reacted with diaminobenzidine or tetramethylbenzidine, counterstained and examined for retrogradely labeled cell bodies. Input projections were observed contralaterally from: all three divisions of cochlear nucleus; intermediate and dorsal nuclei of the lateral lemniscus (LL); and the central nucleus, external nucleus and dorsal cortex of the IC. Input projections were observed ipsilaterally from: the medial and lateral superior olivary nuclei; the superior paraolivary nucleus; the dorsolateral and anterolateral periolivary nuclei; the dorsal and ventral divisions of the ventral nucleus of LL; the dorsal and intermediate nuclei of LL; the central nucleus, external nucleus and dorsal cortex of the IC outside the injection site; and small projections from central gray and the medial geniculate body. These findings in young, adult mice with normal hearing can now serve as a baseline for similar experiments being conducted in mice of older ages and with varying degrees of hearing loss to discover neural changes that may cause age-related hearing disorders.     

Effects of subtle mid-frequency auditory dysfunction upon speech discrimination in noise

Earlier studies have indicated mid-frequency auditory dysfunction and depressed ability to discriminate speech in noise among noise-exposed listeners with high-frequency hearing loss. The present study was designed to determine whether mid-frequency dysfunction contributed to the depressed speech discrimination performance. Normal listeners, and noise-exposed and older listeners with high-frequency hearing loss listened to word lists presented in competing 'cocktail party' noise under unfiltered and low-pass filter conditions. In the low-pass filter condition the performance of the noise-exposed listeners was superior to that normal listeners, indicating that mid-frequency auditory dysfunction on the part of noise-exposed listeners does not contribute to their difficulties discriminating unfiltered speech in noise. The performance of the older listeners was below that of the two other groups in both filtered and unfiltered conditions, indicating greater difficulty discriminating speech than would be predicted only on the basis of high-frequency hearing loss.     

A hierarchical method for generating low-energy conformers of a protein-ligand complex

Auditory cortex of macaque monkeys can be divided into a core of primary or primary-like areas located on the lower bank of the lateral sulcus, a surrounding narrow belt of associated fields, and a parabelt region just lateral to the belt on the superior temporal gyrus. We determined patterns of ipsilateral cortical connections of the parabelt region by placing injections of four to seven distinguishable tracers in each of five monkeys. Results were related to architectonic subdivisions of auditory cortex in brain sections cut parallel to the surface of artificially flattened cortex (four cases) or cut in the coronal plane (one case). An auditory core was clearly apparent in these sections as a 16- to 20-mm rostrocaudally elongated oval, several millimeters from the lip of the sulcus, that stained darkly for parvalbumin, myelin, and acetylcholinesterase. These features were most pronounced caudally in the cortex assigned to auditory area I, only slightly reduced in the rostral area, and most reduced in the narrower rostral extension we define as the rostrotemporal area. A narrow band of cortex surrounding the core stained more moderately for parvalbumin, acetylcholinesterase, and myelin. Two regions of the caudal belt, the caudomedial area, and the mediolateral area, stained more darkly, especially for parvalbumin. Rostromedial and medial rostrotemporal, regions of the medial belt stained more lightly for parvalbumin than the caudomedial area or the lateral belt. The parabelt region stained less darkly than the core and belt fields. Injections confined to the parabelt region labeled few neurons in the core, but large numbers in parts of the belt, the parabelt, and adjacent portions of the temporal lobe. Injections that encroached on the belt labeled large numbers of neurons in the core and helped define the width of the belt. Caudal injections in the parabelt labeled caudal portions of the belt, rostral injections labeled rostral portions, and both caudal and rostral injections labeled neurons in the rostromedial area of the medial belt. These observations support the concept of dividing the auditory cortex into core, belt, and parabelt; provide evidence for including the rostral area in the core; suggest the existence of as many as seven or eight belt fields; provide evidence for at least two subdivisions of the parabelt; and identify regions of the temporal lobe involved in auditory processing.     

Cortical lesions and auditory discrimination.

Reviews studies investigating the effects of lesions of the auditory cortex upon auditory discriminations. Discriminations studied include frequency, intensity, duration and other temporal cues, complex spectral differences, and changes in temporal patterning. Factors determining the effectiveness of lesions are (a) size and completeness of lesion, (b) whether the lesion involved 1 or both hemispheres, (c) nature of the testing procedure, (d) size of the signal differences to be discriminated, and (e) nature of the discrimination. In view of the numerous factors, comparison of different studies is often difficult because of confounding. In terms of the factors listed above, (a) patterning changes, in which signals are not changed but merely rearranged in order of presentation, suffer more than do tasks involving the detection of new signals or the recognition of different signals; and (b) discrimination tasks requiring recognition suffer more than do tasks requiring only the detection of a new signal. It appears probable that the nature of the discrimination task interacts with the locus of the lesion and that failures on different types of tasks reflect different deficits. (58 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Diversity of connections of the temporal neocortex with amygdaloid nuclei in the dog (Canis familiaris)

Reciprocal connections of amygdaloid nuclei with the temporal neocortex in the dog were investigated. Injections of fluorescent tracers and BDA into particular temporal areas were made in eleven dogs. The topographical arrangement of connections and variations in their density differentiate the temporal neocortex in the dog into a few regions. Among them, the cortex involving the anterior part of the ectosylvian gyrus did not send any amygdalopetal projection. The middle ectosylvian, dorsal zone of the posterior ectosylvian and the anterior part of the Sylvian gyrus were weakly connected with the amygdala. The cortical region involving the ventral zone of the posterior ectosylvian and composite posterior areas, as well as posterior Sylvian gyrus, was characterized by profuse connections with the amygdaloid complex. Cortico-amygdaloid connections originate in the wide cortical area of the auditory cortex of the middle and dorsal part of the posterior ectosylvian gyrus as well as in the auditory association cortex located in the ventral ectosylvian, composite posterior and posterior Sylvian gyri. The connections showed a dorso-ventral gradient of increasing density, in the direction of association fields. The most substantial projection taking rise from the ectosylvian posterior and posterior composite gyri terminated preferentially in the pericapsular sector of the lateral amygdaloid nucleus and, to a lesser degree, in its medial sector. Terminals of connections originating in the Sylvian gyrus occupied preferentially the intermediate part of the lateral nucleus, slightly more medially than that from the ectosylvian and posterior composite areas. Additionally, axonal terminals derived from the composite posterior and Sylvian posterior areas were observed in the basal parvocellular and magnocellular nuclei. Neocortical projections were reciprocated by amygdalofugal connections with two exceptions: the basal magnocellular nucleus was distinguished by a substantial amygdalofugal projection to the temporal neocortex focused on the dorsal Sylvian gyrus, and the central nucleus of the amygdala, in contrast, received an exclusively corticofugal projection.     

Human cortico-hippocampal activity related to auditory discrimination revealed by neuromagnetic field

We carried out multi-dipole estimation and pursued spatio-temporal brain activity on a time scale of several milliseconds during an auditory discrimination task using a whole-cortex type SQUID system. Neuronal activities were estimated in the medial (hippocampus, parahippocampal gyrus, etc.) and lateral temporal cortices (superior and middle temporal gyri, etc.), the dorsolateral prefrontal cortex (middle and inferior frontal gyri, etc.) and the parietal cortex (supramarginal gyrus, etc.) in the 280-400 ms latency range. The activity in the posterior hippocampal region was the most prominent and long-lasting in parallel with the activities in the other regions. Therefore, the posterior hippocampal region is a central structure engaged in auditory discrimination. The whole-cortex neuromagnetic measurements provided the possibility of imaging the time-varying activities of the human cortico-hippocampal neural networks.     

Determination of chromium in wine and other alcoholic beverages consumed in spain by electrothermal atomic absorption spectrometry

Using the peak procedure, rats with aspiration lesions to the medial prefrontal cortex (PFC) or the hippocampus were tested for the acquisition of timing behavior and temporal memory. After surgery, rats were 1st trained to discriminate a 40-s interval and then tested for temporal memory with gap trials. Results indicated that lesions to the medial PFC disrupted the acquisition of timing behavior. Medial PFC animals needed significantly more trials to reach criterion, and their temporal discrimination function was less uniform and steep, indicating a general deficit in timing ability. In hippocampal rats, the ability to estimate the duration of the discriminative stimulus was unaffected by the lesion. It was concluded that the hippocampus is not necessary for the acquisition of timing behavior in this task. Gap trials failed to produce a deficit in the memory for temporal events for either lesion. Thus, it was further concluded that neither the medial PFC nor the hippocampus is necessary for the memory of temporal events.     

MRI and brainstem auditory evoked potential evidence of eighth cranial nerve involvement in multiple sclerosis

An MS patient experienced sudden hearing loss. Brainstem auditory evoked potentials, previously normal, showed substantial abnormalities that suggested the impairment of the distal part of the acoustic nerve. MRI detected a small hyperintense lesion along the acoustic nerve; the lesion decreased in size and then disappeared after steroid treatment. This demonstrates that a demyelinating lesion in the distal tract of the eighth cranial nerve may cause an acute hearing loss in MS.     

Functional dissociation of the prefrontal cortex and the hippocampus in timing behavior.

Using the peak procedure, rats with aspiration lesions to the medial prefrontal cortex (PFC) or the hippocampus were tested for the acquisition of timing behavior and temporal memory. After surgery, rats were trained to discriminate a 40-sec interval and then tested for temporal memory with gap trials. Results indicated that lesions to the medial PFC disrupted the acquisition of timing behavior. Medial PFC animals needed significantly more trials to reach criterion, and their temporal discrimination function was less uniform and steep, indicating a general deficit in timing ability. In hippocampal rats, the ability to estimate the duration of the discriminative stimulus was unaffected by the lesion. It was concluded that the hippocampus is not necessary for the acquisition of timing behavior in this task. Gap trials failed to produce a deficit in the memory for temporal events for either lesion. Thus, it was further concluded that neither the medial PFC nor the hippocampus is necessary for the memory of temporal events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prefrontal connections of the parabelt auditory cortex in macaque monkeys

In the present study, we determined connections of three newly defined regions of auditory cortex with regions of the frontal lobe, and how two of these regions in the frontal lobe interconnect and connect to other portions of frontal cortex and the temporal lobe in macaque monkeys. We conceptualize auditory cortex as including a core of primary areas, a surrounding belt of auditory areas, a lateral parabelt of two divisions, and adjoining regions of temporal cortex with parabelt connections. Injections of several different fluorescent tracers and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were placed in caudal (CPB) and rostral (RPB) divisions of the parabelt, and in cortex of the superior temporal gyrus rostral to the parabelt with parabelt connections (STGr). Injections were also placed in two regions of the frontal lobe that were labeled by a parabelt injection in the same case. The results lead to several major conclusions. First, CPB injections label many neurons in dorsal prearcuate cortex in the region of the frontal eye field and neurons in dorsal prefrontal cortex of the principal sulcus, but few or no neurons in orbitofrontal cortex. Fine-grain label in these same regions as a result of a WGA-HRP injection suggests that the connections are reciprocal. Second, RPB injections label overlapping prearcuate and principal sulcus locations, as well as more rostral cortex of the principal sulcus, and several locations in orbitofrontal cortex. Third, STGr injections label locations in orbitofrontal cortex, some of which overlap those of RPB injections, but not prearcuate or principal sulcus locations. Fourth, injections in prearcuate and principal sulcus locations labeled by a CPB injection labeled neurons in CPB and RPB, with little involvement of the auditory belt and no involvement of the core. In addition, the results indicated that the two frontal lobe regions are densely interconnected. They also connect with largely separate regions of the frontal pole and more medial premotor and dorsal prefrontal cortex, but not with the extensive orbitofrontal region which has RPB and STGr connections. The results suggest that both RPB and CPB provide the major auditory connections with the region related to directing eye movements towards stimuli of interest, and the dorsal prefrontal cortex for working memory. Other auditory connections to these regions of the frontal lobe appear to be minor. RPB has connections with orbitofrontal cortex, important in psychosocial and emotional functions, while STGr primarily connects with orbital and polar prefrontal cortex.     

Long latency evoked potentials in a case of corpus callosum agenesia

Following monoaural stimulation, long latency auditory evoked potentials (LLAEPs) recorded from contralateral temporal areas have a shorter latency and larger amplitude than those recorded from the ipsilateral temporal areas. This observation agrees with the operational model drawn up in 1967 by Kimura, which assumes that only anatomically prevailing crossed auditory pathways are active during dichotic hearing, while direct pathways are inhibited. The inputs may then be conveyed to the contralateral cortex, from where they finally reach the ipsilateral temporal areas by means of interhemispheric commissures. It is this mechanism which may underline the right ear advantage for verbal stimuli and the left ear advantage for melodies observed when administering dichotic listening tasks. With the aim of verifying this hypothesis, we recorded temporal LLAEPs in a 21 year-old woman suffering from complex partial seizures, whose CT scan and MRI showed corpus callosum agenesia. Our data support the hypothesis that ipsilateral pathways are greatly inhibited by the contralateral pathways, and therefore auditory stimuli can be supposed to reach the contralateral auditory cortex from where they are transferred through the corpus callosum to the ipsilateral auditory cortex.     

Plasticity of auditory cortex associated with sensorineural hearing loss in adult C57BL/6J mice

The representation of frequency was mapped in the primary auditory cortex (AI) of C57BL/6J (C57) mice during young adulthood (1.5-2 months) when hearing is optimal, and at 3, 6, and 12 months of age, a period during which progressive, high frequency, sensorineural hearing loss occurs in this strain. Maps were also obtained from CBA/CaJ mice which retain good hearing as they age. In AI of young adult C57 mice and CBA mice, characteristic frequencies (CFs) of multiple-unit clusters were easily identified with extracellular recordings, and a general tonotopic organization was observed from dorsal (high frequency) to ventral and caudal (low frequency). In individual cases there appeared to be deviations from the above tonotopic organization, despite the fact that inbred mice are genetically invariant. As progressive loss of high frequency sensitivity ensued peripherally, a substantially increased representation of middle frequencies was observed in AI. There was no apparent change in the surface area of the auditory cortex despite the elimination of high frequencies, and virtually the entire auditory cortex became devoted to the middle frequencies (especially 10-13 kHz) for which sensitivity remained high. Similar age-related changes were not observed in normal-hearing CBA mice. These findings indicate that plasticity in the representation of frequency in AI is associated with high frequency hearing loss in C57 mice.     

Cerebral cortical hyperactivation in response to mental stress in patients with coronary artery disease

The central nervous system (CNS) effects of mental stress in patients with coronary artery disease (CAD) are unexplored. The present study used positron emission tomography (PET) to measure brain correlates of mental stress induced by an arithmetic serial subtraction task in CAD and healthy subjects. Mental stress resulted in hyperactivation in CAD patients compared with healthy subjects in several brain areas including the left parietal cortex [angular gyrus/parallel sulcus (area 39)], left anterior cingulate (area 32), right visual association cortex (area 18), left fusiform gyrus, and cerebellum. These same regions were activated within the CAD patient group during mental stress versus control conditions. In the group of healthy subjects, activation was significant only in the left inferior frontal gyrus during mental stress compared with counting control. Decreases in blood flow also were produced by mental stress in CAD versus healthy subjects in right thalamus (lateral dorsal, lateral posterior), right superior frontal gyrus (areas 32, 24, and 10), and right middle temporal gyrus (area 21) (in the region of the auditory association cortex). Of particular interest, a subgroup of CAD patients that developed painless myocardial ischemia during mental stress had hyperactivation in the left hippocampus and inferior parietal lobule (area 40), left middle (area 10) and superior frontal gyrus (area 8), temporal pole, and visual association cortex (area 18), and a concomitant decrease in activation observed in the anterior cingulate bilaterally, right middle and superior frontal gyri, and right visual association cortex (area 18) compared with CAD patients without myocardial ischemia. These findings demonstrate an exaggerated cerebral cortical response and exaggerated asymmetry to mental stress in individuals with CAD.     

Cortical-hippocampal auditory processing identified by magnetoencephalography

We recorded magnetic and electrical responses simultaneously in an auditory detection task to elucidate the brain areas involved in auditory processing. Target stimuli evoked magnetic fields peaking at approximately the same latency of around about 400 msec (M400) over the anterior temporal, superior temporal, and parietal regions on each hemisphere. Equivalent current dipoles (ECDs) were analyzed with a time-varying multidipole model and superimposed on each subject's magnetic resonance image (MRI). Multiple independent dipoles located in the superior temporal plane, inferior parietal lobe, and mesial temporal region best accounted for the recorded M400 fields. These findings suggest that distributed activity in multiple structures including the mesial temporal, superior temporal, and inferior parietal regions on both hemispheres is engaged during auditory attention and memory updating.     

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 to 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)