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At least 307 records · Page 17Linked to original sources

PubMed2004

Activation of the primary and association auditory cortex by the transition of sound intensity: a new method for functional examination of the auditory cortex in humans.

During functional MRI image acquisition, the scanning equipment generates substantial auditory noise, the effects of which are usually ignored. To investigate the neural activity in response to the transition of noise, we measured cerebral responses to short silent periods (1 and 5 s) during which the slice readout gradients were switched off. In all 15 normal volunteers, the 1 s silence bilaterally activated the primary and association auditory cortex. Subtraction of the response to the 1 s silent period from that to the 5 s silent period revealed the activation related to the onset (transition of sound from OFF to ON) event, indicating that the 1 s response is offset (transition of sound from ON to OFF) related. The complex response of the auditory cortex to the transition of the noise should be considered in designing functional MRI with auditory tasks.

Acoustic Stimulation↗

PubMed2000

Is there an optimal age for recovery from motor cortex lesions? I. Behavioral and anatomical sequelae of bilateral motor cortex lesions in rats on postnatal days 1, 10, and in adulthood.

Rats were given bilateral lesions of the motor cortex on the day of birth (P1), tenth day of life (P10), or in adulthood. They were trained on several motor tasks (skilled forelimb reaching, beam traversing, tongue extension), general motor activity, and a test of spatial learning (Morris water task). Although all lesion groups were impaired at skilled reaching, the P10 group was less impaired than either of the other two lesion groups. Furthermore, on the other motor tests the P10 group did not differ from controls whereas both P1 and adult groups were impaired. Only the P1 lesion group was impaired at the acquisition of the Morris water task. Anatomical analyses revealed that the P1 and P10 rats had smaller brains than the other two groups as well as having a generalized decrease in cortical thickness. Dendritic analysis of layer III pyramidal cells in the parietal cortex revealed a decrease in apical arbor in the lesion groups and an increase in the basilar arbor of the P1 and adult lesion animals. The P1 and adult operated groups showed an increase in spine density in the basilar dendrites of layer V pyramidal cells. Finally, analysis of the pattern of corticospinal projections revealed that the P1 animals had a markedly wider field of corticospinal projection neurons than any of the other groups. The widespread anatomical changes in all lesion groups versus the relatively better behavioral recovery after P10 lesions suggests that day 10 represents an optimal period for adapting to brain damage and subsequent brain reorganization.

Age Factors↗

PubMed2002

Projection from the perirhinal cortex to the frontal motor cortex in the rat.

Stimulation of the anterior perirhinal cortex (PERa) induced marked surface-negative and depth-positive field potentials in the rat frontal motor cortex (MC) including the rostral and caudal forelimb areas. Injection of biotinylated dextran into the PERa densely labeled axon terminals in the superficial layers of the MC, where vigorous unit responses were evoked after PERa stimulation, indicated that the perirhinal-frontal projection preferentially activates the superficial layer neurons of the MC.

Animals↗

PubMed2000

Functional properties of the primary motor cortex and ventral premotor cortex in the monkey during a visually guided jaw-movement task with a delay period.

This study investigated single neuronal activity in the face area of the primary motor cortex (MI) and ventral part of the premotor cortex (PMv) while a monkey performed a visually guided jaw-movement task with a delay period. When the monkey executed the jaw movements, 48 MI and 53 PMv neurons showed statistically significant activities time-locked to jaw movements and were defined as movement-related neurons. The activities of movement-related neurons could be classified into phasic, phasic-tonic and tonic patterns based on the changes in discharge rate. Most of the neurons exhibiting phasic and phasic-tonic activities probably contributed to the initiation of jaw movements, since they exhibited transient responses immediately after the onset of the go-cue indicating the jaw movement. In contrast, the sustained activity of the movement-related neurons exhibiting phasic-tonic and tonic activities may be involved in controlling and/or maintaining jaw position. Sustained activity was also detected during the delay period in 4 MI and 29 PMv neurons and these neurons were defined as set-related neurons. It is thought that these set-related neurons are involved in the preparation for the subsequent jaw movement, since the masticatory muscles showed no significant changes during the delay period. These findings suggest that the MI may be involved predominantly in the initiation and control of jaw movements, and that the PMv may be involved in motor preparation, and may play a role as a higher-order motor area related to the initiation and control of jaw movements.

Animals↗

PubMed1998

Primary motor cortex isolation: complete paralysis with preserved primary motor cortex.

We present a left-sided hemiplegic patient with a cerebrovascular lesion involving the medial part of the right frontal and parietal lobes and the corpus callosum, but sparing the hand area of right primary motor cortex (M1). Several studies using transcranial magnetic stimulation demonstrated functional integrity of the efferent pathways from the right M1, intact sensory afferents to M1, an impairment of transcallosal connection between the bilateral motor cortices, and reduced ipsilateral cortico-cortical inhibition within the right M1. Based on these results, we conclude that the paralysis of this patient was caused by disconnection of the intact M1 from any structures requisite for initiation of movements. The present patient also suggests the importance of various afferents to M1 in voluntary movement. We propose a term of 'primary motor cortex isolation' to designate the paralysis reported here.

Electromyography↗

PubMed2000

Effects of coupled perirhinal cortex and medial septal area, fimbria-fornix, entorhinal cortex tetrodotoxin inactivations on passive avoidance consolidation in the rat.

In order to ascertain the rat perirhinal cortex (PC) function during early consolidation of a passive avoidance response (PAR), and to ascertain whether there are some functional interactions with the medial septal area (MSA), the fimbria-fornix complex (FF) and the entorhinal cortex (EC), PC-MSA, PC-FF, and PC-EC coupled inactivations were performed immediately after the PAR acquisition session. Anesthetized male adult Wistar rats aged 60 days were treated with stereotaxical bilateral injections of TTX (5 ng in 0.5 microl saline) in the appropriate sites. Retrieval testing was performed 48 h later. It was shown that all three coupled inactivations were followed by significant PAR disruption. It may be concluded that PC is somehow active even during the first mnemonic phase following the acquisition session, thus better defining PC mnemonic involvement chronology. These results may be taken as indicating that during initial consolidation the engram is concurrently processed in more than one septal and parahippocampal site, each of which by itself is not absolutely necessary for the final engram formation.

Analysis of Variance↗

PubMed1997

Corticosubthalamic input zones from forelimb representations of the dorsal and ventral divisions of the premotor cortex in the macaque monkey: comparison with the input zones from the primary motor cortex and the supplementary motor area.

Employing double anterograde axonal tracing in combination with intracortical microstimulation, we examined the distribution patterns of corticosubthalamic inputs from forelimb representations of the dorsal (PMd) and ventral (PMv) divisions of the premotor cortex in the macaque monkey. The inputs from the PMd and PMv were distributed mainly in the medial aspect of the subthalamic nucleus (STN), in which their distribution areas overlapped each other. By the same experimental approach, we further compared corticosubthalamic input zones from the PMd/PMv with those from the primary motor cortex (MI) and the supplementary motor area (SMA). The input zones from the PMd/PMv and SMA largely overlapped in the medial aspect of the STN, whereas the input zones from the PMd/PMv and MI were virtually segregated mediolaterally in the STN.

Animals↗

PubMed2002

Activity-dependent changes in synaptophysin immunoreactivity in hippocampus, piriform cortex, and entorhinal cortex of the rat.

Synaptophysin, an integral membrane glycoprotein of synaptic vesicles, has been widely used to investigate synaptogenesis in both animal models and human patients. Kindling is an experimental model of complex partial seizures with secondary generalization, and a useful model for studying activation-induced neural growth in adult systems. Many studies using Timm staining have shown that kindling promotes sprouting in the mossy fiber pathway of the dentate gyrus. In the present study, we used synaptophysin immunohistochemistry to demonstrate activation-induced neural sprouting in non-mossy fiber cortical pathways in the adult rat. We found a significant kindling-induced increase in synaptophysin immunoreactivity in the stratum radiatum of CA1 and stratum lucidum/radiatum of CA3, the hilus, the inner molecular layer of the dentate gyrus, and layer II/III of the piriform cortex, but no significant change in layer II/III of the entorhinal cortex, 4 weeks after the last kindling stimulation. We also found that synaptophysin immunoreactivity was lowest in CA3 near the hilus and increased with increasing distance from the hilus, a reverse pattern to that seen with Timm stains in stratum oriens following kindling. Furthermore, synaptophysin immunoreactivity was lowest in dorsal and greatest in ventral sections of both CA3 and dentate gyrus in both kindled and non-kindled animals. This demonstrates that different populations of sprouting axons are labeled by these two techniques, and suggests that activation-induced sprouting extends well beyond the hippocampal mossy fiber system.

Animals↗

PubMed2003

The ipsilateral human motor cortex can functionally compensate for acute contralateral motor cortex dysfunction.

What promotes motor recovery from stroke? To date, studies of recovery from stroke have shown alterations in function in various cortical areas, including the contralesional (unaffected) motor cortex (M1). However, whether these changes contribute to recovery or are mere epiphenomena remains unclear. We therefore sought evidence that the ipsilateral M1 can compensate for dysfunction of the contralateral M1. We recorded the change in force production during a finger-tapping task in response to acute disruption of M1 function by repetitive transcranial magnetic stimulation (rTMS). Neither control (occipital) nor ipsilateral M1 rTMS lead to a change in tapping force. RTMS over contralateral M1 had a short-lived effect and induced changes in ipsilateral M1 excitability around the time that these behavioral effects abated, consistent with delayed compensation by the ipsilateral M1. Simultaneous bilateral M1 stimulation, designed to prevent compensation by the ipsilateral M1, had a large and prolonged effect on tapping force. This is the first demonstration that the ipsilateral primary motor cortex is capable of functionally significant compensation for focal contralateral cortical dysfunction in the adult human and provides a rational basis for interventional treatments aimed at promoting functional compensation in unaffected cortical areas after stroke.

Biomechanical Phenomena↗

PubMed1996

Involvement of entorhinal cortex or parietal cortex in long-term spatial discrimination memory in rats: retrograde amnesia.

Twenty-four rats assigned to 1 of 3 matched groups (control, entorhinal cortex [EC], and parietal cortex [PC]) were trained on 6 successive discrimination problems (2 in an 8-arm for pretraining and 4 in a 12-arm radial maze for training per se). The training on the 12-arm maze started 6, 4, 2, and 0.5 weeks before surgery. On the day after the rats learned the last problem, they were given surgery according to groups. Postoperative retention was measured by presenting 16 trials per session for each of the problems during 4 sessions. Results indicate that the EC lesions produced a retention deficit for problems learned immediately and up to 4 weeks before surgery, but not for the problem acquired 6 weeks before the lesions. The PC lesions produced a significant retrograde amnesia that was not temporally graded. Results demonstrate that the EC and PC make important, albeit distinct, contributions to spatial memory storage and retrieval in rats.

Amnesia, Retrograde↗

PubMed1970

Mescaline-induced changes of brain-cortex ribosomes. Effect of mescaline on the stability of brain-cortex ribosomes.

1. During the action of mescaline sulphate on goat brain-cortex slices the ribosomal particles become susceptible to breakdown, releasing protein, RNA, acidsoluble nucleotides and ninhydrin-positive materials, resulting in loss of ribosomal enzyme activities. 2. Ribosomes of the mescaline-treated cortex slices undergo rapid degradation in the presence of trypsin and ribonuclease. 3. Mescaline does not alter the chemical and nucleotide compositions or the u.v.-absorption characteristics of ribosomal particles, however.

Animals↗

PubMed2003

Competition and representation during memory retrieval: roles of the prefrontal cortex and the posterior parietal cortex.

In this functional-MRI study we examined the hypothesis that the prefrontal cortex responds differently to the extent of competition during retrieval, whereas the parietal cortex is responsible for problem representation that should not be directly related to the competition. Participants mastered arbitrary person-location pairs, and their recognition memory was tested in a functional-MRI session. The pairs were constructed such that a person was associated with one, two, or three different locations and vice versa. The recognition time increased with the number of associations, reflecting increased competition. A confirmatory analysis of imaging data with prespecified prefrontal and parietal regions showed that, although both regions were highly involved during memory retrieval, only the prefrontal region responded to the levels of competition. This result was consistent with predictions of an information-processing model as well as with an exploratory identification of regions of interest.

Adult↗

PubMedDate not supplied

The functional organization of local circuits in visual cortex: insights from the study of tree shrew striate cortex.

We have used a combination of anatomical and physiological techniques to explore the functional organization of vertical and horizontal connections in tree shrew striate cortex. Our studies of vertical connections reveal a remarkable specificity in the laminar arrangement of the projections from layer IV to layer III that establishes three parallel intracortical pathways. The pathways that emerge from layer IV are not simple continuations of parallel thalamocortical pathways. Layer IV and its connections with layer II/III restructure the inputs from the LGN, combining the activity from ON and OFF channels and from the left and right eye and transmit the products of this synthesis to separate strata within the overlying layers. In addition, studies of two other prominent vertical connection pathways, the projections from layer VI to layer IV and from layer II/III to layer V suggest that the parallel nature of these systems is perpetuated throughout the cortical depth. Our studies of horizontal connections have revealed a systematic relationship between a neuron's orientation preference and the distribution of its axon arbor across the cortical map of visual space. Horizontal connections in layer II/III extend for greater distances and give rise to a greater number of terminals along an axis of the visual field map that corresponds to the neuron's preferred orientation. These findings suggest that the contribution of horizontal inputs to the response properties of layer II/III neurons is likely to be greater in regions of visual space that lie along the axis of preferred orientation (endzones) than along the orthogonal axis (side zones). Topographically aligned horizontal connections may contribute to the orientation preference of layer II/III neurons and could account for the axial specificity of some receptive field surround effects. Together, these results emphasize that specificity in the spatial arrangement of local circuit axon arbors plays an important role in shaping the response properties of neurons in visual cortex.

Animals↗

PubMed1996

Projection pattern of single corticocortical fibers from the parietal cortex to the motor cortex.

Arborization of single corticocortical (CC) axons projecting from the parietal cortex to the motor cortex (Mx) was analysed using an intraaxonal staining technique in the cat. Stem axons arising from cell bodies in area 5 ramified repeatedly into numerous terminal branches in the Mx, forming 2-6 patches (0.2-0.8 mm in diameter) separated by a terminal-free gap. Axon terminals were distributed mainly in layers II and III and sparsely in layers V, VI and I. This feature is quite similar to that of thalamocortical axons and other corticocortical fibres. Thus the patchy organization may be a basic input structure for afferents of the Mx and play a role in generation of adequate motor output patterns in the Mx.

Animals↗

PubMed2006

Effects of small ischemic lesions in the primary motor cortex on neurophysiological organization in ventral premotor cortex.

After a cortical lesion, cortical areas distant from the site of injury are known to undergo physiological and anatomical changes. However, the mechanisms through which reorganization of distant cortical areas is initiated are poorly understood. In a previous publication, we showed that the ventral premotor cortex (PMv) undergoes physiological reorganization after a lesion destroying the majority of the primary motor cortex (M1) distal forelimb representation (DFL). After large lesions destroying >50% of the M1 DFL, the PMv DFL invariably increased in size, and the amount of the increase was positively correlated with the size of lesion. To determine whether lesions destroying <50% of the M1 DFL followed a similar trajectory, we documented PMv reorganization using intracortical microstimulation techniques after small, ischemic lesions targeting subregions within the M1 DFL. In contrast to earlier results, lesions resulted in a reduction of the PMv DFL regardless of their location. Further, because recent anatomical findings suggest a segregation of PMv connectivity with M1, we examined two lesion characteristics that may drive alterations in PMv physiological reorganization: location of the lesion with respect to PMv connectivity and relative size of the lesion. The results suggest that after a lesion in the M1 DFL, the induction of representational plasticity in PMv, as evaluated using intracortical microstimulation, is related more to the size of the lesion than to the disruption of its intracortical connections.

Animals↗

PubMed2003

Facilitation from ventral premotor cortex of primary motor cortex outputs to macaque hand muscles.

We demonstrate that in the macaque monkey there is robust, short-latency facilitation by ventral premotor cortex (area F5) of motor outputs from primary motor cortex (M1) to contralateral intrinsic hand muscles. Experiments were carried out on two adult macaques under light sedation (ketamine plus medetomidine HCl). Facilitation of hand muscle electromyograms (EMG) was tested using arrays of fine intracortical microwires implanted, respectively, in the wrist/digit motor representations of F5 and M1, which were identified by previous mapping with intracortical microstimulation. Single pulses (70-200 microA) delivered to F5 microwires never evoked any EMG responses, but small responses were occasionally seen with double pulses (interval: 3 ms) at high intensity. However, both single- and double-pulse stimulation of F5 could facilitate the EMG responses evoked from M1 by single shocks. The facilitation was large (up to 4-fold with single and 12-fold with double F5 shocks) and occurred with an early onset, with significant effects at intervals of only 1-2 ms between conditioning F5 and test M1 stimuli. A number of possible pathways could be responsible for these effects, although it is argued that the most likely mechanism would be the facilitation, by cortico-cortical inputs from F5, of corticospinal I wave activity evoked from M1. This facilitatory action could be of considerable importance for the coupling of grasp-related neurons in F5 and M1 during visuomotor tasks.

Animals↗

PubMed1995

Behavioural consequences of frontal cortex grafts and enriched environments after sensorimotor cortex lesions.

Past studies have experienced difficulty in achieving graft survival and behavioural recovery after sensorimotor cortex lesions. In the present work, adult female rats trained preoperatively to cross a narrow beam for food reward were maintained in standard group cages or an enriched environment, commencing one week after a unilateral lesion. One month post-lesion, half of these rats received multiple suspension grafts of (E20) fetal frontal cortex, placed adjacent to the lesion cavity, and 8 days later recovery of beam-walking skills was examined for a six-week period. The grafts survived in all cases with an appropriate lesion, a notable result given the one month lesion-graft delay, but graft volume was not influenced by postoperative environment. The substantial lesion-induced deficits evident just prior to differential housing showed a marked reduction by the start of post-graft testing, but relative to intact controls a persistent deficit in foot slip errors occurred in all lesion groups. Irrespective of graft status, postoperative enrichment prevented the occurrence of severe foot slips, especially early in retraining. The frontal grafts, however, enhanced beam-walking recovery by reducing the overall frequency of foot slips on early post-grafting sessions, an effect we suggest is related to graft-derived trophic influences, but this measure was not significantly improved by postoperative enrichment.

Animals↗

PubMed2006

Medial profrontal cortex and anterior cingulate cortex in the generation of alpha activity induced by transcendental meditation: a magnetoencephalographic study.

Previous EEG studies have shown that transcendental meditation (TM) increases frontal and central alpha activity. The present study was aimed at identifying the source of this alpha activity using magnetoencephalography (MEG) and electroencephalography (EEG) simultaneously on eight TM practitioners before, during, and after TM. The magnetic field potentials corresponding to TM-induced alpha activities on EEG recordings were extracted, and we attempted to localize the dipole sources using the multiple signal classification (MUSIC) algorithm, equivalent current dipole source analysis, and the multiple spatio-temporal dipole model. Since the dipoles were mapped to both the medial prefrontal cortex (mPFC) and anterior cingulate cortex (ACC), it is suggested that the mPFC and ACC play an important role in brain activity induced by TM.

Adult↗