Dual streams of auditory afferents target multiple domains in the primate prefrontal cortex.

'What' and 'where' visual streams define ventrolateral object and dorsolateral spatial processing domains in the prefrontal cortex of nonhuman primates. We looked for similar streams for auditory-prefrontal connections in rhesus macaques by combining microelectrode recording with anatomical tract-tracing. Injection of multiple tracers into physiologically mapped regions AL, ML and CL of the auditory belt cortex revealed that anterior belt cortex was reciprocally connected with the frontal pole (area 10), rostral principal sulcus (area 46) and ventral prefrontal regions (areas 12 and 45), whereas the caudal belt was mainly connected with the caudal principal sulcus (area 46) and frontal eye fields (area 8a). Thus separate auditory streams originate in caudal and rostral auditory cortex and target spatial and non-spatial domains of the frontal lobe, respectively.

Serial and parallel processing in rhesus monkey auditory cortex.

Auditory cortex on the exposed supratemporal plane in four anesthetized rhesus monkeys was mapped electrophysiologically with both pure-tone (PT) and broad-band complex sounds. The mapping confirmed the existence of at least three tonotopic areas. Primary auditory cortex, AI, was then aspirated, and the remainder of the cortex on the supratemporal plane was remapped. PT-responses in the caudomedial area, CM, were abolished in all animals but one, in which they were restricted to the high-frequency range. Some CM sites were still responsive to complex stimuli. In contrast to the effects on CM, no significant changes were detectable in the rostral area, R. After mapping cortex in four additional monkeys, injections were made with different tracers into matched best-frequency regions of AI, R, and CM. Injections in AI and R led to retrograde labeling of neurons in all three subdivisions of the medial geniculate (MG) nucleus (MGv, MGd, and MGm), as well as nuclei outside MG, whereas CM injections led to only sparse labeling of neurons in a restricted zone of the lateral MGd and, possibly, MGm, in addition to labeling in non-MG sites. The combined results suggest that MGv sends direct projections in parallel to areas AI and R, which drive PT-responses in both areas. PT-responses in area CM, however, appear to be driven by input relayed serially from AI. The direct input to CM from MGd and other thalamic nuclei may thus be capable of mediating responses only to broad-band sounds.

The origin, course, and termination of the hippocampothalamic projections in the macaque.

The projections from the hippocampal formation to the thalamus were investigated with both anterograde and retrograde tracers. Horseradish peroxidase was injected into medial and midline thalamic sites in six cases, and tritiated amino acids were injected into the hippocampal formation in nine others, five of which had prior transections of the fornix. Only the subicular and entorhinal cortices were found to project to the thalamus. From the subicular cortex, dense bilateral projections were traced through the fornix to the anterior nuclei, while lighter fornical projections terminated in other rostral midline sites, including the nuclei reuniens, centralis latocellularis, and paraventricularis. These projections arose predominantly from the polymorphic cells which are located in the deepest cellular layers of the subiculum and prosubiculum. In addition, the subicular cortex was found to project to the nucleus lateralis dorsalis. The latter projection, which showed evidence of a crude topographic organization, ran either through the fornix or, unlike the other subicular efferents, through the sublenticular limb of the internal capsule to form part of the temporopulvinar bundle of Arnold. The nonfornical projection to the nucleus lateralis dorsalis passed through the medial pulvinar, where there was some additional termination. Few, if any, projections from the entorhinal cortex to the thalamus travelled in the fornix. Rather, the entorhinal efferents were carried in the inferior thalamic peduncle to the magnocellular portion of the nucleus medialis dorsalis, and in the internal capsule and bundle of Arnold to the medial pulvinar and the nucleus lateralis dorsalis.

Subcortical projections of area MT in the macaque.

Area MT is a visuotopically organized area in extrastriate cortex of primates that appears to be specialized for the analysis of visual motion. To examine the full extent and topographic organization of the subcortical projections of MT in the macaque, we injected tritiated amino acids in five cynomolgus monkeys and processed the brains for autoradiography. The injection sites, which we identified electrophysiologically, ranged from the representation of central through peripheral vision in both the upper and lower visual fields and included, collectively, most of MT. Projections from MT to the superior colliculus are topographically organized and in register with projections from striate cortex to the colliculus. Unlike projections from striate cortex, those from MT are not limited to the upper layer of the stratum griseum superficiale but rather extend ventrally from the upper through the lower layer of the stratum griseum superficiale and even include the stratum opticum. Projections from MT to the pulvinar are organized into three separate fields. One field (P1) is located primarily in the inferior pulvinar but extends into a portion of the adjacent lateral pulvinar. The second field (P2) partially surrounds the first and is located entirely in the lateral pulvinar. The third and heaviest projection field (P3) is located posteromedially in the inferior pulvinar but also includes small portions of the lateral and medial pulvinar that lie dorsal to the brachium of the superior colliculus. While projections from MT to P1 and P2 are topographically organized, there appears to be a convergence of MT inputs to P3. Projections from MT to the reticular nucleus of the thalamus are located in the ventral portion of the nucleus, approximately at the level of the caudal pulvinar. There was some evidence that MT sites representing central vision project more caudally than do those representing peripheral vision. Projections from MT to the caudate, putamen, and claustrum are localized to small, limited zones in each structure. Those to the caudate terminate within the most caudal portion of the body and the tail. Similarly, projections to the putamen are always to its most caudal portion, where the structure appears as nuclear islands. Projections to the claustrum are located ventrally, approximately at the level of the anterior part of the dorsal lateral geniculate nucleus. Projections from MT to the pons terminate rostrally in the dorsolateral nucleus, the lateral nucleus, and the dorsolateral portion of the peduncular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections of the amygdala to the thalamus in the cynomolgus monkey.

The projections of the amygdala to the thalamus in cynomolgus monkeys (Macaca fascicularis) were studied with both anterograde and retrograde axonal tracing techniques. Horseradish peroxidase (HRP) was injected into medial and midline thalamic sites in five animals, and tritiated amino acids were injected into selected amygdaloid regions in a total of 13 hemispheres in ten animals. The findings from the two types of tracer experiments demonstrated the origins, course, and terminal pattern of amygdaloid projections to two thalamic nuclei--medialis dorsalis (MD) and reuniens. Almost all of the amygdaloid nuclei contribute projections to MD, though the greatest proportion arise from the basal group and terminate in discrete, interlocking patches within the medial, magnocellular portion of MD. In addition to this major projection, the central and medial amygdaloid nuclei send a lighter projection to the lateral portion of nucleus reuniens. The amygdalothalamic projections took a variety of routes out of the amygdala before the large majority joined the inferior thalamic peduncle and entered the rostral head of the thalamus where they turned caudally toward their targets. A small number of amygdalothalamic fibers may also run in the stria terminalis.

Memory impairments following restricted medial thalamic lesions in monkeys.

Thalamic contributions to memory were assessed in monkeys with lesions placed in the medial portions of either the anterior or posterior thalamus (AMT and PMT, respectively). Both lesions produced a moderate impairment in a test of object recognition memory. Furthermore, all three animals in the PMT group and two out of the three in the AMT group were moderately impaired on a test of object-reward associative memory. Comparison of these results with those of a previous study in which the AMT and PMT regions were removed jointly (Aggleton and Mishkin 1983) suggests that damage in either region can induce a memory loss but that combined damage to both is required to produce a full-blown amnesia.

A memory system in the monkey.

A neural model is presented, based largely on evidence from studies in monkeys, postulating that coded representation of stimuli are stored in the higher-order sensory (i.e. association) areas of the cortex whenever stimulus activation of these areas also triggers a cortico-limbo-thalamo-cortical circuit. This circuit, which could act as either an imprinting or rehearsal mechanism, may actually consist of two parallel circuits, one involving the amygdala and the dorsomedial nucleus of the thalamus, and the other the hippocampus and the anterior nuclei. The stimulus representation stored in cortex by action of these circuits is seen as mediating three different memory processes: recognition, which occurs when the stored representation is reactivated via the original sensory pathway; recall, when it is reactivated via any other pathway; and association, when it activates other stored representations (sensory, affective, spatial, motor) via the outputs of the higher-order sensory areas to the relevant structures.

Effects of damage to the suprachiasmatic area of the anterior hypothalamus on the daily melatonin and cortisol rhythms in the rhesus monkey.

The effects of lesions of the suprachiasmatic nucleus (SCN) on the circadian rhythms in melatonin and cortisol were examined in the rhesus monkey. The concentrations of the two hormones were monitored in cerebrospinal fluid (CSF) withdrawn from two sham-operated animals, two animals with complete bilateral SCN lesions, and two animals with partial SCN damage at 4 and 8 months after surgery. In the sham-operated animals, as in the intact animal, the daily melatonin rhythm was entrained to the daily light-dark cycle, was suppressed in constant light, and persisted in constant darkness. In contrast, neither animal with complete SCN ablation exhibited a daily pattern of CSF melatonin in diurnal lighting at 4 months after surgery nor were their melatonin levels at constant low values. Furthermore, CSF melatonin concentrations were not suppressed in either animal by constant light. Surprisingly, at 8 months after surgery, spectral analysis revealed a 24-hr component to the melatonin patterns for each animal with complete SCN ablation in both diurnal lighting and constant darkness. The two animals with partial SCN damage exhibited a daily melatonin rhythm in diurnal lighting, but constant light did not suppress CSF melatonin concentrations consistently. Daily rhythms persisted in both for a 6 1/2-d period of study in constant darkness. In contrast to the alterations in the melatonin rhythm after SCN damage, there was no apparent effect of either partial or complete SCN ablation on the daily CSF cortisol rhythm. These data indicate that, in the rhesus monkey, the SCN is important for the generation, photic entrainment, and photic suppression of the melatonin rhythm. However, circadian oscillators located outside of the SCN region may control the normal daily cortisol rhythm and perhaps the melatonin rhythm in the absence of the SCN.

An approach to the performance of contrast studies in contrast material-reactive persons.

A method of carrying out contrast studies was considered for use in 124 persons with past histories of adverse reactions to contrast media. High-dosage steroid treatment was given before and during the contrast study to 37 patients with previous rash responses and 9 with prior anaphylactoid reactions; only 3 and 1 patients, respectively, of these groups had mild adverse reactions. Patients with past reactions deemed "vasomotor" underwent contrast study without preparative drug therapy without significant adverse effects. Although uncontrolled, this study suggests a possible protective role of steroids in patients with certain previous reactions to contrast media. We do not wish to imply that this is the only approach that can be used in the kind of patients reported here.

Hematoma from arteriovenous malformation producing hydrocephalus and simulating a thalamic tumor. Report of two cases.

Two patients with a history of progressive unilateral neurological symptoms and signs, and evidence of obstructive hydrocephalus from a mass lesion adjacent to the third ventricle as demonstrated by pneumography, were each found to have an intracerebral hematoma secondary to remote hemorrhage from a small vascular malformation. One patient died shortly after surgical exploration and the other after ventriculography. The pathophysiology of hydrocephalus associated with a vascular malformation is discussed and the need for considering a benign cause for obstructive hydrocephalus from a mass deep in the brain substance is emphasized.