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PubMed1993

[Morphometric studies on the cortex and medulla of frontally sectioned kidneys in the Japanese adult].

The cortex and medulla areas, sectioned frontally, of 50 kidneys from 25 dissecting cadavers were measured to determine the correlation between differences in sex, laterality, and age. The average parenchyma (cortex + medulla) area was 33.45 +/- 9.16 cm2 and was larger in men than women; there was no significant laterality, but the parenchyma area was negatively correlated with age. The average cortex area was 20.39 +/- 5.80 cm2 and was also larger in men than women; laterality was not significant, and the cortex area was negatively correlated with age. The average medulla area was 13.05 +/- 4.40 cm2, and no significant difference in sex or laterality was found. The medulla area was negatively correlated with age. Additionally, the average number of renal pyramids (medulla) was 6.24 +/- 1.45 on these sections. Difference in the average areas of cortex and medulla was significant. The medulla was exceptionally larger in two cases (4%). The ratio between the average area of the cortex and medulla (C/M ratio) was 1.67 +/- 0.56. No sex difference or laterality was found, nor was there a correlation between the C/M ratio and age or kidney size. The sectioned area of cortex was approximately 1.5 to 2 times larger than medulla. These results suggest that senile atrophy may occur at the same rate in the renal cortex as in the medulla.

Adult↗

PubMed1995

[Motor reorganization in the motor cortex].

Plasticity within the human central motor system has been studied with transcranical magnetic stimulation in patients with peripheral and central nervous diseases. In 4 patients with a complete upper limb palsy due to traumatic cervical root avulsion, surgical anastomosis of intercostal to musculocutaneous nerves was performed to restore function in the biceps brachii muscle. The motor unit discharges became independent from respirations gradually over 1 to 2 years. Motor cortex mapping of the reinnervated biceps muscle showed a gradual change over 4 to 33 months from the area of the intercostal muscles to that of the arm area, which was more lateral on the motor cortex. These findings suggest that reorganization of the motor cortex to arm flexor muscles occurs following peripheral nerve anastomosis. In 8 patients with chronic cerebral infarction with hemiplegia. Four of 8 patients did not show MEPs in paralytic hand muscles by contralateral cortex stimulation, but showed small MEPs by ipsilateral cortex stimulation. These cases had the huge cortical infarction unilaterally in CT. Another four of 8 patients showed small MEPs in paralytic hand muscles by contralateral cortex stimulation, but no MEPs by ipsilateral cortex stimulation. These cases had the subcortical infarction unilaterally in CT. These findings suggest that reorganization of motor cortex following unilateral cerebral infarction.

Anastomosis, Surgical↗

PubMed1997

NMDA receptor and the tyrosine phosphorylation of its 2B subunit in taste learning in the rat insular cortex.

We demonstrate that the NMDA receptor is involved in taste learning in the insular cortex of the behaving rat and describe two facets of this involvement. Blockage of the NMDA receptor in the insular cortex by the reversible antagonist APV during training in a conditioned taste aversion (CTA) paradigm impaired CTA memory, whereas blockage of the NMDA receptor in an adjacent cortex or before a retrieval test had no effect. When rats sampled an unfamiliar taste and hence learned about it, either incidentally or in the context of CTA training, the tyrosine phosphorylation of the NMDA receptor subunit 2B (NR2B) in the insular cortex was specifically increased. The level of tyrosine phosphorylation on NR2B was a function of the novelty of the taste stimulus and the quantity of the taste substance consumed, properties that also determined the efficacy of the taste stimulus as a conditioned stimulus in CTA; however, blockage of the NMDA receptor by APV during training did not prevent tyrosine phosphorylation of NR2B. We suggest that tyrosine phosphorylation of NR2B subserves encoding of saliency in the insular cortex during the first hours after an unfamiliar taste is sampled and that this encoding is independent of another, necessary role of NMDA receptors in triggering experience-dependent modifications in the insular cortex during taste learning. Because a substantial fraction of the NR2B protein in the insular cortex seems to be expressed in interneurons, saliency and the tyrosine phosphorylation of NR2B correlated with it may modulate inhibition in cortex.

Animals↗

PubMed1997

Rhinal cortex removal produces amnesia for preoperatively learned discrimination problems but fails to disrupt postoperative acquisition and retention in rhesus monkeys.

To test whether the rhinal cortex (i.e., entorhinal and perirhinal cortex) plays a time-limited role in information storage, eight rhesus monkeys were trained to criterion on two sets of 60 object discrimination problems, one set at each of two different time periods separated by 15 weeks. After the monkeys had learned both sets, two groups balanced for preoperative acquisition rates were formed. One group received bilateral ablation of the rhinal cortex (n = 4), and the other was retained as an unoperated control group (n = 4). After a 2 week rest period, monkeys were assessed for retention of the object discrimination problems. Retention was significantly poorer in monkeys with removals of the rhinal cortex relative to the controls (68 vs 91%). Although both groups showed slightly better retention of problems from the more recently learned set, there was no evidence of a differential effect of the cortical removal across sets (i.e., no temporal gradient). In addition, the monkeys with rhinal cortex lesions subsequently learned three new sets of 10 object discrimination problems as quickly as the controls did, thus ruling out the possibility of a gross impairment in visual perception or discrimination abilities. Furthermore, they retained these postoperatively learned object discriminations as well as the controls did. The findings indicate that the rhinal cortex is critical for the storage and/or retrieval of object discrimination problems that were learned up to 16 weeks before rhinal cortex ablation; however, in the absence of the rhinal cortex, efficient learning and retention of new discrimination problems can still occur.

Amnesia, Retrograde↗

PubMed1994

Rat posterior parietal cortex: topography of corticocortical and thalamic connections.

Anatomical and functional findings support the contention that there is a distinct posterior parietal cortical area (PPC) in the rat, situated between the rostrally adjacent hindlimb sensorimotor area and the caudally adjacent secondary visual areas. The PPC is distinguished from these areas by receiving thalamic afferents from the lateral dorsal (LD), lateral posterior (LP), and posterior (Po) nuclei, in the absence of input from the ventrobasal complex (VB) or dorsal lateral geniculate (DLG) nuclei. Behavioral studies have demonstrated that PPC is involved in spatial orientation and directed attention. In the present study we used fluorescent retrograde axonal tracers primarily to investigate the cortical connections of PPC, in order to determine the organization of the circuitry by which PPC is likely to participate in these functions, and also to determine how the topography of its thalamic connections differs from that of neighboring cortical areas. The cortical connections of PPC involve the ventrolateral (VLO) and medial (MO) orbital areas, medial agranular cortex (area Fr2), portions of somatic sensory areas Par1 and Par2, secondary visual areas Oc2M and Oc2L, auditory area Te1, and retrosplenial cortex. The secondary visual areas Oc2L and Oc2M have cortical connections which are similar to those of PPC, but are restricted within orbital cortex to area VLO, and within area Fr2 to its caudal portion, and do not involve auditory area Te1. The cortical connections of hindlimb cortex are largely restricted to somatic sensory and motor areas. Retrosplenial cortex, which is medially adjacent to PPC, has cortical connections that are prominent with visual cortex, do not involve somatic sensory or auditory cortex, and include the presubiculum. We conclude that PPC is distinguished by its pattern of cortical connections with the somatic sensory, auditory and visual areas, and with areas Fr2, and VLO/MO, in addition to its exclusive thalamic connectivity with LD, LP and Po. Because recent behavioral studies indicate that PPC, Fr2 and VLO are involved in directed attention and spatial learning, we suggest that the interconnections among these three cortical areas represent a major component of the circuitry for these functions in rats.

Animals↗

PubMed1982

Pattern of projection and physiological properties of cortico-cortical connections from the posterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons lying along the posterior bank of the ansate sulcus and the projection of these neurons to area 4 gamma of the motor cortex of the cat were studied and the following results were obtained: (1) Short latency antidromic responses were recorded from neurons along the medial-lateral bank of the posterior ansate sulcus following intracortical microstimulation (ICMS) delivered to motor cortex, area 4 gamma. (2) The posterior ansate region projects topographically to the motor cortex. Neurons in the most medial part of the ansate region project to the medial part of 4 gamma, while neurons in the central and lateral parts of the ansate region project to the more lateral parts of area 4 gamma. (3) In 33 cases, receptive field information was available for both the antidromically activated ansate neuron and from neurons around the stimulating site in 4 gamma. In 58% of the cases, both cortical sites received afferent input from within the same part of the periphery. (4) Afferent input to the motor cortex was examined following combined ablations of the primary somatosensory cortex (SI) and third somatosensory cortex (SIII) including all of area 5. We conclude that the integrity of these cortical regions is not necessary for afferent input to reach the motor cortex.

Afferent Pathways↗

PubMed1975

Electrophysiological studies of the projections from the parietal association area to the cerebellar cortex.

1. Responses evoked in the cerebellar cortex by stimulation of the parietal association cortex (rostral portions of the middle suprasylvian gyrus) were recorded and analysed in cats, and were compared with those by stimulation of the motor cortex (anterior sigmoid gyrus). 2. The parietal stimulation elicited early mossy fibre and late climbing fibre responses in the cerebellar cortex. The mossy fibre responses appeared at a latency of 2.0--2.5 msec and predominantly in the lateral (hemispherical) part of the contralateral cerebellum (mainly crus I, crus II and paramedian lobules). Cutting of the inferior cerebellar peduncle produced little or no influence upon the mossy fibre responses, which suggests that the mossy fibre responses are mediated chiefly by the pontine nuclei. 3. The climbing fibre responses were recorded at a latency of 17--19 msec and markedly in the contralateral intermediate and medial parts of IV--VI lobules. The responses were easily sppressed by anaesthesia and depended on the conditions of experimental animals. The unstable appearance of the responses and their longer latencies than those of the climbing fibre responses due to stimulation of the motor cortex imply indirect pathways from the parietal association cortex to the inferior olive. 4. The predominant projection of the parietal-induced mossy fibre responses to the lateral part of the cerebellum was compared with the mossy fibre projection from the motor cortex and was discussed as an important component in the cerebrocerebellar loops.

Animals↗

PubMedDate not supplied

Electrical activity of isolated rabbit cerebral cortex after direct application of acetylcholine.

Six weeks after surgical isolation of an extensive region of the rabbit neocortex, chronic experiments were carried out to study the EEG spectrum in baseline conditions and after macroapplication of acetylcholine (ACh) to the isolated cortex. Application of ACh elicited a complex, multiphasic response in the sensorimotor and visual regions of the isolated cortex, which lasted more than 10 min and consisted of an increase in the EEG amplitude with a gradual alteration in rhythmicity: there was an increase in theta activity, and higher-frequency (up to 15 Hz) processes appeared in the EEG trace. In control experiments (rabbits with intact cortex), application of ACh increased the EEG spectral amplitude and peak height. The response of the isolated cortex was interpreted as artificially induced activation, the level of activation determining the EEG spectrum. The differences in the responses of the isolated cortex and intact cortex result from preservation of control of the intact cortex by subcortical structures.

Acetylcholine↗

PubMed1982

The axo-axonic interneuron in the cerebral cortex of the rat, cat and monkey.

The synaptic connections of a specific type of identified cortical interneuron, the axo-axonic cell, were studied using Golgi methods. In the light-microscope axo-axonic cells were demonstrated in certain layers of the primary and secondary visual cortex of rat, cat and monkey, in the motor cortex of cat and in the subiculum and pyriform cortex of rat. The dendrites originating from the oval soma were oriented radially in a lower and upper spray within a cylinder about 100-150 microns wide. Electron-microscopy of Golgi impregnated, gold-toned axo-axonic cells showed predominantly but not exclusively asymmetrical synaptic contacts on their dendrites and spines, few synaptic contacts on the perikarya some of which were asymmetrical, and no synaptic contacts on the axon initial segment. The axon usually arborized within the vicinity of the cell's own dendritic field in an area 100-200 microns in diameter. In the kitten motor cortex the axon of a neuron in layer III descended to layer VI, providing a columnar arborization. The axon formed specialized, 10-50 microns long terminal segments invariably oriented parallel with the axon initial segment of pyramidal cells. All 85 identified symmetrical-type synaptic contacts, deriving from 31 specialized terminal segments, were found exclusively on the axon initial segment of pyramidal neurons. Rare, lone boutons of axo-axonic cells also made synaptic contact only with axon initial segments, confirming the exclusive target specificity of these cells. In identified gold-toned boutons, flattened pleomorphic vesicles were present. Electron-microscopy showed that axons ending in specialized terminal segments may originate from myelinated fibres, indicating that Golgi impregnation has revealed only part of the axon. Counting of axon terminal segments, each of which was in contact with the axon initial segment of a pyramidal neuron, revealed 166 pyramidal neurons receiving input from a partially reconstructed axo-axonic cell in the motor cortex of the kitten, and 67 from another cell in the visual cortex of the cat. The convergence of five axo-axonic cells onto one pyramidal cell was demonstrated in the striate cortex of the cat by counting all synaptic contacts on three initial segments. Cells from a one-month-old kitten were compared with those of the adult. The axon of the developing neurons was more diverse, having many growth cones and filopodia which made no specialized membrane contacts. However, the developing specific terminal segments formed synapses only with axon initial segments. It is concluded that the presence of axo-axonic cells in all the species and cortical areas we have examined suggests their association with the structural design of pyramidal cells, wherever the latter occur, and with their participation in the information processing of pyramidal cells. Axo-axonic cells are uniquely endowed with the means of simultaneously influencing the action potential at the site of origin in groups of pyramidal cells...

Animals↗

PubMed1996

Perirhinal cortex involvement in limbic kindled seizures.

Investigations into the anatomical substrate of temporal lobe epilepsy have yielded a number of important observations regarding the involvement of the piriform and perirhinal cortical areas in temporal lobe seizure propagation. Although early reports indirectly suggested that the circuits of the piriform cortex might act as a critical conduit for limbic seizure discharges to access motor systems, recent reports more strongly implicate the perirhinal cortex in this process. In the following report, we provide a brief summary of the earlier work involving the piriform cortex and its potential involvement in kindled limbic seizures. This is followed then by the results of several recent in vivo and in vitro electrophysiological studies that ascribe a critical importance for the perirhinal cortex in convulsive limbic seizures. Finally, since our anatomical studies indicated that the perirhinal cortex densely innervates the frontal motor cortex, we examined the involvement of this latter region in amygdala kindled seizures using the reversible functional lesion of cortical spreading depression. Based on these findings we suggest that the circuits of the perirhinal cortex may be important in the amplification and distribution of temporal lobe seizure discharges, providing access to structures that are capable of driving a convulsive response.

Amygdala↗

PubMed1991

Guidance of callosal axons by radial glia in the developing cerebral cortex.

During development, columns of the mammalian cerebral cortex are formed by migration of neurons along fascicles of radial glia. Subsequently, axons of the corpus callosum connect reciprocal regions of each cerebral hemisphere. To determine whether the radial growth of callosal afferents through the developing cortex may be guided by particular cellular elements, we examined the ultrastructural relationship between callosal afferents and radial fibers in the early postnatal hamster sensorimotor cortex. Developing callosal axons and their growth cones were labeled with HRP injected into the cortex at 3 d postnatal when the growth cones have extended across the callosum and are just entering the contralateral cortex. An EM analysis of 30 HRP-labeled axons and their growth cones revealed that they extended upon fascicles of radial processes associated with migrating neurons. Reconstruction of seven of these growth cones, serially sectioned in their entirety, showed that growth cones were associated with the same radial fascicle as their axon. Growth cones also touched other cellular elements such as axons. However, the finding that callosal afferents, from the point at which they enter the cortex to their growth cones, were apposed to a continuous fascicle of radial fibers suggests that callosal axons are tracking along radial processes. We conclude that the majority of the radial processes within fascicles are likely to be glial, based on their relatively large diameters, electron-lucent cytoplasm with a regular array of microtubules, the presence of glycogen granules, occasional cytoplasmic protrusions lacking microtubules, and their consistent association with migrating neurons. We propose therefore that radial glia may serve a guidance function for growing callosal axons in their radial trajectory through the developing cerebral cortex.

Animals↗

PubMed1999

Perirhinal cortex projections to the amygdaloid complex and hippocampal formation in the rat.

The differential efferent projections of the perirhinal cortex were traced by using anterograde and retrograde tracing techniques. The dorsal bank cortex (area 36) projected lightly to the lateral entorhinal cortex and more strongly to the lateral, posterolateral cortical, and posterior basomedial amygdaloid nuclei and amygdalostriatal transition zone. The ventral bank (dorsolateral entorhinal cortex) projected to the lateral entorhinal cortex, dorsal subiculum, and subfield CA1 and mainly targeted the basolateral amygdaloid nucleus. Corticocortical projections from the dorsal and ventral banks targeted different cortical areas. The fundus of the rhinal sulcus (area 35) projected to both lateral and medial entorhinal cortices, ventral subiculum, lateral and basolateral nuclei, and amygdalostriatal transition zone. Corticocortical projections targeted areas projected to by both dorsal and ventral banks and also by second somatosensory area, first temporal cortical area, and striate cortex. Neurons projecting to the lateral nucleus were distributed in all layers of the dorsal bank, wheras those projecting to CA1 and subiculum were found in superfical layers (mostly layer III) of the ventral bank. Projections to the basolateral nucleus arose from superfical layers (mostly layer II) of the fundus and deep layers of the ventral bank. Furthermore, projections to the amygdala mostly arose from rostral levels, whereas hippocampal projections primarily originated caudally. The rat perirhinal cortex is heterogeneous in its efferent connectivity, and distinct projections arise from the dorsal and ventral banks and fundus of the rhinal sulcus. The widespread cortical connectivity of the fundus suggests that only this part of the perirhinal cortex is similar to area 35 of the primate brain.

Amygdala↗

PubMed1985

Cytoarchitectonic development of the prefrontal cortex in the rat.

This paper gives an account of the cytoarchitectonic characteristics that make it possible to delineate, from as early as day 6, different subareas of the prefrontal cortex of the rat. Three phases can be distinguished during postnatal development. The first phase (from day 1 until day 18) is dominated by differentiation of the neurons within the cortical plate and by the formation of the cortical layers. At day 1, regional differences are observed in the cytoarchitecture of the cortical plate which correspond to the future subareas of the prefrontal cortex. The formation of layer IV occurs in the dorsolateral cortex around day 6, and from this age the agranular prefrontal cortex is well demarcated from the other parts of the frontal cortex. Between day 6 and day 10, the cortical plate has disappeared and all cortical layers can be recognized in the prefrontal cortex. Differentiation of the cells within the cortical layers changes the cytoarchitectonic character of the layers through day 18. During the second phase (from day 18 until day 30) little change occurs in the cytoarchitectonic characteristics of the prefrontal subareas. During the third phase (from day 30 until day 90) the delineation of the cortical layers becomes less clear in Nissl-stained sections, and the individual cytoarchitectonic variance increases. On the basis of cytoarchitectonic criteria it can be concluded that the orbital prefrontal cortex develops earlier than does the medial prefrontal cortex.

Aging↗

PubMed1993

Regional and laminar organization of projections from the presubiculum and parasubiculum to the entorhinal cortex: an anterograde tracing study in the rat.

The regional and laminar organization of the projections from the presubiculum and the parasubiculum to the entorhinal cortex was analyzed in the rat with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). The projections from the presubiculum were bilateral and confined to layers III and I of the medial entorhinal area (MEA). Both the ispi- and the contralateral projections showed similar distributions and were almost of equal density. Projections to layer III of the entorhinal cortex arose predominantly from superficial layers of the presubiculum, whereas the fibers that reach layer I of the entorhinal cortex appear to originate preferentially from the deep layers of the presubiculum. These fibers also appeared to innervate weakly layer II of MEA. The parasubiculum distributed projections not only to MEA but also to the lateral entorhinal area (LEA), innervating layer II selectively. The innervation of LEA was quite dense and extensive. Very weak projections from the parasubiculum to the contralateral entorhinal cortex were observed in this study. The position of the terminal plexus in the entorhinal cortex was determined by the point of origin along both the dorsoventral and transverse or proximodistal axes of the presubiculum and parasubiculum. Projections from the presubiculum and parasubiculum entered the entorhinal cortex at the level of the injection, or slightly ventral to it, and the main terminal field was always present ventrally to the injection site. The dorsoventral axis of origin thus corresponded to a similarly oriented axis of termination in the entorhinal cortex. The distribution in relation to the origin along the transverse axis was more complex, and differences between the presubiculum and parasubiculum were present. The proximal presubiculum, i.e., the part closest to the subiculum, projected to the most lateral part of MEA and the central part of the presubiculum sent fibers to the most medial part of MEA. The distal part of the presubiculum, i.e., the part that borders the parasubiculum, projected to the central part of MEA. Projections from the portion of the parasubiculum directly adjacent to the presubiculum, the so-called proximal parasubiculum, reached medial parts of MEA, and those originating in the central part distributed preferentially to lateral parts of MEA and adjacent medial parts of LEA. The distal part of the parasubiculum that borders the entorhinal cortex projected mainly to almost the full mediolateral extent of LEA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

Cortex, a Drosophila gene required to complete oocyte meiosis, is a member of the Cdc20/fizzy protein family.

Mutations in cortex and grauzone cause abnormal arrest in Drosophila female meiosis. cortex was mapped to a 14 kb interval in 26F-27A by the male recombination mapping method. While these experiments mapped the gene accurately, they also illustrated some complexities of this method. Rescue results showed that a 2.8 kb genomic fragment from this interval was able to fully rescue the cortex phenotype. The 2.8 kb rescuing fragment contains a single open reading frame. The predicted amino acid sequence indicates that cortex encodes a WD-repeat protein and is a distant member of the Cdc20 protein family. Results from a developmental Northern analysis showed that the cortex transcript is expressed at high levels during oogenesis and early embryogenesis. Interestingly, the meiotic metaphase-anaphase II arrest defect in embryos laid by cortex homozygous females resembles the mitotic metaphase-anaphase defects observed in yeast cdc20 mutants. The predicted nature of the Cortex protein, together with the observed meiotic phenotype in cortex mutants, suggest that a similar pathway to the cdc20 dependent APC-mediated proteolysis pathway, which governs the metaphase-anaphase transition in mitosis, is also important in regulating oocyte meiosis.

Alleles↗

PubMed1998

Specific invasion of occipital-to-frontal neocortical grafts by axons from the lateral posterior thalamic nucleus consecutive to neonatal lesion of the rat occipital cortex.

Previous work found that transplants of embryonic (E) day 16 occipital cortex placed into the frontal cortex of newborn hosts failed to receive input from visual-related nuclei of the host thalamus. The present study is aimed at determining the possible causes of the lack of visual-related thalamic input to these transplants. For that purpose, a retrograde neurotracer was injected into transplants of embryonic (E16) occipital origin which were placed into the frontal cortex of newborn rats with either intact or damaged occipital cortex. In rats with intact occipital cortex, occipital-to-frontal transplants were indeed not contacted by axons from the dorsal lateral geniculate (DLG) nucleus and received only sparse to negligible input from, respectively, the lateral posterior (LP) and laterodorsal (LD) thalamic nuclei. Yet, following neonatal lesion of the host occipital cortex, the occipital-to-frontal transplants received a significant input from the LP and to a much lesser degree from the LD but practically none from the DLG. Additional control cases with frontal-to-frontal transplants and prior lesion of the occipital cortex did not receive significant input from any of these thalamic nuclei. Thus, following neonatal deprivation of cortical target cells in their main terminal field, LP and to a lesser extent LD axons have the capacity to recognize and significantly innervate appropriate targets even those at some distance from their normal terminal site. DLG neurons degenerate or are not able to contact and invade available terminal space that is provided at some distance from the occipital cortex.

Animals↗

PubMed1994

Dissociated effects of perirhinal cortex ablation, fornix transection and amygdalectomy: evidence for multiple memory systems in the primate temporal lobe.

Four experiments were performed with macaque monkeys (rhesus, Macaca mulatta, and cynomolgus, M. fascicularis). In experiment 1 six rhesus monkeys learned pre-operatively to perform delayed matching-to-sample, with complex naturalistic scenes as the stimulus material. Three of these monkeys then received bilateral ablations of the perirhinal cortex, while the other three received fornix transection. Both groups showed an impairment postoperatively, but the effect of perirhinal cortex ablation was significantly more severe than the effect of fornix transection. In experiment 2 the same animals, together with three normal, control rhesus monkeys, which had a similar training history, performed simple, spatial discrimination learning in a Wisconsin General Test Apparatus. The animals with fornix transection were impaired, but the animals with ablations of perirhinal cortex were not. In experiment 3 the nine animals from experiment 2 were tested for the acquisition of systematic preferences among four novel foods (apple, lemon, olive, meat). Their results were compared with those from a previously published experiment with normal and amygdalectomized cynomolgus monkeys which had been given the same food preference test. Amygdalectomy produced a significant disruption of food preference learning but the other two lesions (fornix transection and perirhinal cortex ablation) did not. In experiment 4, 16 rhesus monkeys (9 normal controls, 4 with perirhinal cortex ablation, and 3 with fornix transection) learned to discriminate among complex naturalistic scenes, in a task in which each scene was presented only once per day in the main part of the experiment. The two operated groups were impaired, and there was no significant difference between the severity of the impairments. Thus, the effects of perirhinal cortex ablation can be doubly dissociated from the effects of fornix transection (experiments 1 and 2) and both can be dissociated from the effects of amygdalectomy (experiment 3). Furthermore, the results of experiment 4 show that the effects of perirhinal cortex ablation are not limited to tasks of memory over short retention intervals. On the basis of the presently reported data and other known effects of perirhinal cortex ablation, it is suggested that this ablation produces an impairment in knowledge (semantic memory) about objects.

Amygdala↗

PubMed1993

Neuronal activity related to visual recognition memory: long-term memory and the encoding of recency and familiarity information in the primate anterior and medial inferior temporal and rhinal cortex.

Recordings of the activity of 2705 single neurones were made in entorhinal and perirhinal cortex, area TG of the temporal lobe, and the inferior temporal cortex both during monkeys' performance of a serial recognition memory task using complex pictures and when monkeys were shown objects. Responses of 120 (9.7%) of the visually responsive neurons recorded were significantly smaller to the second than to the first presentations of unfamiliar stimuli. The incidence of such responses was highest in perirhinal cortex plus areas TE1 and TE2 of the temporal lobe, intermediate in lateral entorhinal cortex and areas TE3 and TG, and lowest in other parts of entorhinal and inferior temporal cortex. Response decrements were maintained across 20 or more intervening presentations of other stimuli for the majority of the neurones tested. Responses of 43 (14.4%) of the visually responsive neurones tested were significantly greater to unfamiliar than to highly familiar stimuli. Such differential responses were found only in lateral entorhinal and perirhinal cortex plus areas TG, TE1, TE2 and TE3. For 6 neurones the response difference was significant even when the familiar stimuli had not been seen for more than 24 h: such neurones demonstrate access to information stored in long-term memory for more than 24 h. Seven familiarity neurones signalled information concerning the relative familiarity of stimuli but not information concerning how recently they were last seen; 58 recency neurones signalled information concerning the recency of presentation of stimuli, but not their relative familiarity. Thus certain neurones demonstrate the separable encoding of recency and familiarity information. Neurones signalling information of use for recognition memory are found in cortex close to the rhinal sulcus where lesions result in major deficits in the performance of recognition memory tasks. The conjunction of these findings provides strong evidence for the importance of these neurones and this cortex for processes (recency and familiarity discrimination) necessary for recognition and working memory. The possible relation of the neuronal responses to priming memory is also discussed.

Animals↗