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PubMed1979

Thalamic projections to the feline motor cortex studied with horseradish peroxidase.

Cells in the thalamus projecting to the distal forelimb regions of the motor cortex, area 3a, and the sensory cortex were identified with horseradish peroxidase (HRP). These cortical areas were defined by mapping evoked potentials from superficial and deep radial nerve stimulation. Following injections into the motor cortex, the labelled cells were distributed throughout a large region (greater than 2 mm wide) in the ventral portion of the ventral lateral nucleus (VL). The border area between VL and the ventral posterolateral nucleus (VPL) also contained labelled cells. The region containing labelled cells following injections into area 3a was in the rostral, dorsal VPL, and overlapped with the region containing cells labelled by injections into the motor cortex. Cells labelled by injections into the sensory cortex were near the center of VPL distinctly separated from those labelled after injections into either area 3a or the motor cortex.

Animals↗

PubMed1981

Stimulation induced changes in extracellular free calcium in normal cortex and chronic alumina cream foci of cats.

Changes in extracellular [Ca2+]0 (delta Ca) were measured with ion selective microelectrodes in the sensorimotor cortex of cats, surrounding alumina cream lesions and in the contralateral homotopic cortex. The lesions were produced by topical application of alumina cream 6 months-6 years prior to experiments. In normal cortex, stimulus induced reactions of [Ca2+]0 were found to be maximal (up to 0.45 mM) in depths of 200-300 micrometers below the cortical surface. At depths of 600 micrometers and more below the cortical surface, [Ca+2]0 usually rose by up to 0.2 mM above baseline. In the vicinity of the chronic lesion as well as in contralateral cortex [Ca2+]0 fell initially during stimulation in all depths. Close to the lesion delta Ca was as high as 0.8 mM and sites of maximal delta Ca were found to be located deeper in the cortex. About 5 mm from the scar as well as in the contralateral homotopic cortex, maximum delta Ca levels were found in a depth of 200-300 micrometers. It is suggested that Ca2+ dependent mechanisms are involved in epileptogenesis in chronic epileptic foci.

Aluminum↗

PubMed1995

Right vs. left sensorimotor cortex suction-ablation in the rat: no difference in beam-walking recovery.

The ability of rats to traverse a narrow elevated beam has been used to quantitate recovery of hindlimb motor function after unilateral injury to the sensorimotor cortex. We tested the hypothesis that the rate of spontaneous beam-walking recovery varies with the side of the cortex lesion. Groups of rats that were trained at the beam-walking task underwent suction-ablation of either the right or left hindlimb sensorimotor cortex. There was no difference in hindlimb motor function between the groups on the first post-operative beam-waking trial carried out the day after cortex ablation and no difference between the groups in overall recovery rates over the next two weeks. Subsequent analyses of lesion surface parameters showed no differences in lesion size or extent. Regardless of the side of the lesion, there were also no differences between the right and left hemispheres in norepinephrine content of the lesioned or contralateral cortex. We conclude that the side of sensorimotor cortex ablation injury does not differentially affect the rate of spontaneous motor recovery as measured with the beam-walking task.

Animals↗

PubMed1991

Trajectory of redirected corticospinal axons after unilateral lesion of the sensorimotor cortex in neonatal rat; a phaseolus vulgaris-leucoagglutinin (PHA-L) tracing study.

The corticospinal neurons of the rat project almost exclusively to the contralateral spinal cord. Retrograde and anterograde tracing experiments showed that only about 2-4% of the corticospinal neurons of the sensorimotor cortex project to the ipsilateral spinal cord in the normal rat. The large majority of corticospinal axons (more than 90%) travel at spinal level at the base of the contralateral dorsal funiculus; in addition a few axons run in the contralateral lateral funiculus and at the base of the dorsal horn. The undecussated axons run in the ipsilateral dorsal (about 1-2%) and ventral (about 1-2%) funiculi. The rearrangement of the corticospinal projections was studied with various tracing methods in rats subjected to unilateral lesion of the sensorimotor cortex at Postnatal Day 2 to 4. Spinal injections of the tracer WGA-HRP that were restricted to the side opposite to the cortical lesion showed a significant increase of retrogradely labeled corticospinal neurons in the intact cortex as compared to the proportion of ipsilateral projections in control experiments. This was consistent with an increased density of anterogradely labeled corticospinal terminals in the spinal cord ipsilateral to an injection of WGA-HRP in the motor cortex opposite to neonatal lesion, in comparison to normal rats. The trajectory of these "aberrant" ipsilateral corticospinal projections resulting from the neonatal lesion of the opposite sensorimotor cortex was analyzed by means of the anterograde tracer phaseolus vulgaris-leucoagglutinin (PHA-L), injected in the motor cortex. These data indicated that decussated corticospinal axons recross at spinal levels, close to their terminal zone, where they appear to ramify and terminate in the spinal gray including the motoneurons. Such recrossing axons thus represent one new possible mechanism, among other previously reported ones, contributing to the increase of ipsilateral corticospinal projections in rats subjected to neonatal cortical lesion.

Animals↗

PubMed1989

Distribution of major neurotransmitter receptors in the motor and somatosensory cortex of the rhesus monkey.

The in vitro quantitative autoradiographic technique was used to characterize the distributions of alpha 1, alpha 2, beta 1 and beta 2 adrenergic, D1 and D2 dopaminergic, 5-HT1 and 5-HT2 serotonergic, M1 and M2 cholinergic, GABAA and benzodiazepine receptors in the motor (Brodmann's area 4) and somatosensory (Brodmann's areas 3, 1 and 2) cortex of the adult rhesus monkey. All receptor subtypes studied were present throughout all layers of both areas. In the somatosensory cortex, each receptor had its own laminar distribution. Some subtypes of the same receptor (5-HT1 and 5-HT2; alpha 1 and alpha 2) had complementary distributions while others (beta 1 and beta 2; D1 and D2; M1 and M2) had largely overlapping distributions. In contrast, different receptors had remarkably coincidental distributions in the motor cortex. In this area, they all tended to concentrate in layers I, II and the upper part of layer III. However, such coextensive distribution of many types of neurotransmitter receptors is not observed in motor cortex of rats and humans and therefore may be a distinctive feature of motor cortex in the rhesus monkey. The findings described in this paper indicate that somatosensory and motor areas are distinct in their receptor architecture and that receptor autoradiography provides a useful complement to classical histological techniques in elucidating areal differences in the cortex.

Animals↗

PubMed1990

Raccoon forelimb motorsensory cortex: I. Somatic afferent inputs to different cytoarchitectonic areas.

The distribution of potentials evoked in and around forelimb MsI by graded electrical stimulation of forelimb nerves has been studied in the raccoon (Procyon lotor). These data have been correlated with cytoarchitectonic characteristics of pericruciate cortical tissue. Potentials evoked by cutaneous nerve stimulation were widely distributed in MsI and SmI, but were smaller in amplitude and of longer latency in MsI than in SmI. Stimulation of ulnar, median or deep radial nerve at 1-1.4T, a strength considered to activate only Group I muscle afferent fibers, caused evoked potentials in a localized region mostly confined to posterior sigmoid gyrus. On the basis of cytoarchitectonic features it is concluded that: a) Anterior sigmoid gyrus, to near the level of the tip of the cruciate sulcus, is area 6 cortex; b) The lateral portion of the posterior sigmoid gyrus, cortex comprising the caudal bank of the cruciate sulcus and cortex surrounding the lateral tip of the cruciate sulcus is area 4 cortex; c) The middle portion of the posterior sigmoid gyrus, almost to the lip of the cruciate sulcus rostrally and extending onto the rostral bank of the ascending coronal and postcruciate sulci caudally, is area 3a cortex. The cortical focus for Group I afferent-evoked potentials coincides with area 3a cortex. It is concluded that forelimb MsI of raccoon is organized in a fashion similar to MsI of cats and monkeys.

Animals↗

PubMed2006

Motor experience with graspable objects reduces their implicit analysis in visual- and motor-related cortex.

Motor-related regions of parietal and prefrontal cortices have been shown to selectively activate when observers passively view objects that afford manual grasping. Yet, it remains unknown whether these cortical responses depend on prior motor-related experience with the object being observed. To address this question, we asked participants to undergo fMRI scanning while viewing exemplars of two different categories of graspable objects: one associated with extensive motor experience (door knobs) and one associated with no self-reported motor experience (artificial rock climbing holds). Despite participants' lack of experience grasping climbing holds, these objects were found to generate a systematic response in several visuomotor-related regions of cortex-including left PMv and left AIP. Interestingly, however, the response to door knobs did not include activity in any motor-related regions, being limited instead to a comparatively small bilateral area of lateral occipital cortex, relative to the more spatially extensive response in occipital and temporal cortex that was observed for climbing holds. This result suggested that object-specific responses in both visual- and motor-related cortex may in fact negatively correlate with object-specific motor experience. To test this possibility, we repeated the experiment using participants having extensive self-reported experience grasping climbing holds (i.e., veteran indoor rock climbers). Consistent with our hypothesis, both climbing holds and door knobs generated activity limited to lateral occipital cortex. Taken together, these data support the proposal that repeated real-world motor experience with an object category may lead to reduced implicit analysis in both motor- and visual-related regions of cortex.

Adolescent↗

PubMed2005

Local networks in visual cortex and their influence on neuronal responses and dynamics.

Networks of neurons in the cerebral cortex generate complex outputs that are not simply predicted by their inputs. These emergent responses underlie the function of the cortex. Understanding how cortical networks carry out such transformations requires a description of the responses of individual neurons and of their networks at multiple levels of analysis. We focus on orientation selectivity in primary visual cortex as a model system to understand cortical network computations. Recent experiments in our laboratory and others provide significant insight into how cortical networks generate and maintain orientation selectivity. We first review evidence for the diversity of orientation tuning characteristics in visual cortex. We then describe experiments that combine optical imaging of orientation maps with intracellular and extracellular recordings from individual neurons at known locations in the orientation map. The data indicate that excitatory and inhibitory synaptic inputs are summed across the cortex in a manner that is consistent with simple rules of integration of local inputs. These rules arise from known anatomical projection patterns in visual cortex. We propose that the generation and plasticity of orientation tuning is strongly influenced by local cortical networks-the diversity of these properties arises in part from the diversity of neighbourhood features that derive from the orientation map.

Animals↗

PubMed2004

Local landmark-based mapping of human auditory cortex.

Mammalian sensory cortex is functionally partitioned into cortical fields that are specialized for different processing operations. In theory, averaging functional and anatomical images across subjects can reveal both the average anatomy and the mean functional organization of sensory regions. However, this averaging process must overcome at least two obstacles: (1) the relative locations and sizes of cortical sensory areas vary in different subjects so that across-subject averaging introduces spatial smearing; (2) the relative locations and sizes of cortical areas vary between hemispheres, making it difficult to compare activations between hemispheres or to combine activations across hemispheres. These difficulties are particularly acute for small cortical regions such as auditory cortex. In whole-brain averaging procedures, considerable intersubject variance in the location and orientation of auditory cortex is introduced by variance of the size and shape of structures outside auditory cortex. Here, we compared these global methods with local landmark-based methods (LLMs) that use warping based on local anatomical landmarks. In comparison to maps made with global methods, LLMs produced anatomical maps of auditory cortex with clearer gyral and sulcal structure, and produce functional maps with improved resolution. These results suggest that LLMs have significant advantages over global mapping procedures in studying the details of auditory cortex organization.

Adult↗

PubMed2000

Molecular signalling pathways in the cerebral cortex are required for retrieval of one-trial avoidance learning in rats.

Rats were implanted bilaterally with cannulae in the CA1 region of the dorsal hippocampus, the entorhinal cortex, anterior cingulate cortex, posterior parietal cortex, or the basolateral complex of the amygdala. The animals were trained in one-trial step-down inhibitory avoidance and tested 24 h later. Prior (10 min) to the retention test, through the cannulae, they received 0.5 microl infusions of a vehicle (2% dimethylsulfoxide in saline), or of the following drugs dissolved in the vehicle: the glutamate NMDA receptor blocker, aminophosphonopentanoic acid (AP5, 2.0 or 5.0 microg), the AMPA receptor blocker, 6,7-dinitroquinoxaline-2,3 (1H,4H)dione (DNQX, 0.4 or 1.0 microg), the metabotropic receptor antagonist, methylcarboxyphenylglycine (MCPG, 0.5 or 2.5 microg), the inhibitor of cAMP-dependent protein kinase (PKA), Rp-cAMPs (0.1 or 0.5 microg), the PKA stimulant, Sp-cAMPs (0.5 microg), or the inhibitor of the mitogen-activated protein kinase (MAPK), PD098059 (10 or 50 microM). All these drugs, at the same doses, had been previously found to alter long-term memory formation of this task. Here, retrieval test performance was blocked by DNQX, MCPG, Rp-cAMPs and PD098059 and enhanced by Sp-cAMPs infused into CA1 or the entorhinal cortex. The drugs had similar effects when infused into the parietal or anterior cingulate cortex, except that in these two areas AP5 also blocked retrieval, and in the cingulate cortex DNQX had no effect. Infusions into the basolateral amygdala were ineffective except for DNQX, which hindered retrieval. None of the treatments that affected retrieval had any influence on performance in an open field or in a plus maze; therefore, their effect on retention testing can not be attributed to an influence on locomotion, exploration or anxiety. The results indicate that the four cortical regions studied participate actively in, and are necessary for, retrieval of the one-trial avoidance task. They require metabotropic and/or NMDA glutamate receptors and PKA and MAPK activity. In contrast, the basolateral amygdala appears to participate only through a maintenance of its regular excitatory transmission mediated by glutamate AMPA receptors.

2-Amino-5-phosphonovalerate↗

PubMed2003

Long-term potentiation in visual cortical projections to the medial prefrontal cortex of the rat.

In order to investigate neural mechanisms by which the prefrontal cortex adaptively modifies its activities based on past experience, we examined whether or not sensory cortical projections to the medial prefrontal cortex support long-term potentiation (LTP) in rats. Monosynaptic projections from the secondary visual cortex, mediomedial area (V2MM) to the infralimbic cortex were confirmed by orthodromic as well as antidromic activation of single units. High-frequency stimulation (50 Hz, 2 s) induced LTP (approximately 45% increase over the baseline) in the V2MM projection to the infralimbic cortex. LTP induction in this pathway was completely blocked by an injection (i.p.) of CPP, an N-methyl-D-aspartate receptor antagonist. LTP was also induced in the ventral hippocampal projection to the infralimbic cortex by the same high-frequency stimulation. The present results suggest that modification of synaptic weights of afferent sensory cortical projections is one mechanism underlying learning-induced changes in prefrontal cortical neural activities.

Animals↗

PubMed2000

Functional asymmetry of human prefrontal cortex in verbal and non-verbal episodic memory as revealed by fMRI.

Functional neuroimaging studies have demonstrated preferential involvement of bilateral prefrontal cortex during episodic memory encoding and retrieval. The aim of the present study is to address the question whether left prefrontal model for encoding holds when highly non-verbal material is used, and which region of the brain is critically related to successful retrieval. To do this, seven normal subjects were investigated using functional magnetic resonance imaging (fMRI) during encoding and retrieval of word and checkerboard pattern. Our results revealed that word encoding activated the left prefrontal cortices and right cerebellum, whereas pattern encoding activated the bilateral middle frontal gyrus, superior parietal lobule, premotor area, and occipital visual cortex. Word-specific activation was found in the ventral prefrontal cortices, and pattern-specific activation located in the right dorsal prefrontal cortex. Conjunction analysis during encoding of word and pattern showed that activity in the left dorsal prefrontal cortex and the right cerebellum might relate to common neural network for encoding regardless of the type of material. Finally, the present study demonstrates strong association between the left ventral prefrontal cortex and retrieval success for word. The evidence, that both encoding and retrieval of words activated the left ventral prefrontal cortex, indicates that this area is involved in active and strategic operation of the mnemonic representation. A lack of the right prefrontal activation during retrieval was interpreted as that activity in this region might relate to retrieval effort rather than success.

Adult↗

PubMed1997

Somatosensory evoked potential identification of sensorimotor cortex in removal of intracranial neoplasms.

OBJECTIVE: To assess the ease and reliability of routine use of somatosensory evoked potentials (SSEPs) for identification of sensorimotor cortex in brain tumour removal and to document its influence on the performance and outcome of surgery. METHODS: SSEPs in response to contralateral median nerve stimulation were recorded from the cortical surface by means of a four lead electrode strip. Polarity reversal of short latency SSEP waves was used to identify the position of the central sulcus in 46 consecutive craniotomies for removal of metastases, gliomas, or meningiomas located in, near, or overlying sensorimotor cortex. RESULTS: SSEPs were successfully recorded in 43/46 cases (94%) with demonstration of polarity reversal in 42/43 (98%). SSEP localization led to modification of 14/42 (33%) procedures, most frequently because of either displacement or involvement of sensorimotor cortex by tumour. Six patients (14%) developed new neurological deficits but none of these was attributable to incorrect identification of sensorimotor cortex. CONCLUSIONS: SSEP polarity reversal is a simple, reliable, accurate, and inexpensive method of localizing sensorimotor cortex under general anaesthesia. Correct identification is possible when sensorimotor cortex is displaced or when surface anatomy is obscured by tumour. Routine use of this technique should be considered in all procedures for lesions located near the central sulcus.

Adult↗

PubMed1989

Function of the dorsal and medial cortex of turtles in learning.

The effects of damage to the dorsal and medial cortex of turtles were investigated in two experiments. In the first, damage to the dorsal cortex disrupted acquisition and reversal of a go-no-go discrimination but had no effect on retention of the discrimination if it had been learned preoperatively. Medial cortex damage had no effect. In the second experiment, dorsal cortex damage impaired acquisition, but not extinction or reacquisition, of a discrete-trial keypress. Again, medial cortex damage had no effect. The results suggest that the dorsal cortex is involved in learning in turtles.

Afferent Pathways↗

PubMed1979

Specific distribution of metabolic alterations in cerebral cortex following apomorphine administration.

The topographic distribution of dopaminergic receptors in the cerebral cortex closely parallels that of the dopaminergic innervation. In the rat, dopaminergic axons which originate in the mesencephalon are confined to a few discrete regions of the neocortex--anterior cingulate cortex, entorhinal cortex, frontal cortex (particularly anteromedial and supragenual areas) and the transitional zone between the neocortex and the pyriform cortex. Moreover, biochemical examinations of processes generally considered to be indicative of dopaminergic neuro-transmission--neuronal uptake of labelled dopamine or dopamine-activation of adenylate cyclase activity--have confirmed a highly restricted locus of action of dopaminergic systems in the cerebral cortex. We describe here data obtained using the 2-deoxyglucose technique in conjunction with conventional neuropharmacological techniques, suggesting that the influence of dopaminergic systems on cortical function extends beyond the known confines of the mesocortical dopaminergic system.

Animals↗

PubMed2003

Group II metabotropic glutamate receptor modulation of DOI-induced c-fos mRNA and excitatory responses in the cerebral cortex.

Recent studies have demonstrated that the hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) enhances glutamatergic transmission in the prefrontal cortex. This increase can be suppressed by metabotropic glutamate2/3 (mGlu2/3) receptor activation. In addition to enhancing glutamatergic transmission, DOI increases cortical c-fos expression. We tested if a reduction in glutamate release produced by mGlu2/3 receptor activation attenuates DOI-induced c-fos expression in the cortex. Similar to previous studies, DOI produced a robust increase in c-fos mRNA throughout the cortex, including the prefrontal, frontoparietal, and somatosensory regions. Pretreatment with the mGlu2/3 agonist LY379268 attenuated the DOI-induced increase in the prefrontal cortex. This suppression was blocked by the mGlu2/3 antagonist LY341495. In contrast, the DOI-induced increase in c-fos mRNA in the frontoparietal and somatosensory cortex was unaffected by the mGlu2/3 agents. These findings suggest that Group II metabotropic glutamate receptor agonists are capable of modulating postsynaptic function preferentially in the limbic cortex under conditions of enhanced glutamate release.

Amino Acids↗

PubMed2001

Fos imaging reveals differential neuronal activation of areas of rat temporal cortex by novel and familiar sounds.

To provide information about the possible regions involved in auditory recognition memory, this study employed an imaging technique that has proved valuable in the study of visual recognition memory. The technique was used to image populations of neurons that are differentially activated by novel and familiar auditory stimuli, thereby paralleling previous studies of visual familiarity discrimination. Differences evoked by novel and familiar sounds in the activation of neurons were measured in different parts of the rat auditory pathway by immunohistochemistry for the protein product (Fos) of the immediate early gene c-fos. Significantly higher counts of stained neuronal nuclei (266 +/- 21/mm2) were evoked by novel than by familiar sounds (192 +/- 17/mm2) in the auditory association cortex (area Te3; AudA). No such significant differences were found for the inferior colliculus, primary auditory cortex, postrhinal cortex, perirhinal cortex (PRH), entorhinal cortex, amygdala or hippocampus. These findings are discussed in relation to the results of lesion studies and what is known of areas involved in familiarity discrimination for visual stimuli. Differential activation is produced by novel and familiar individual stimuli in sensory association cortex for both auditory and visual stimuli, whereas the PRH is differentially activated by visual but not auditory stimuli. It is suggested that this latter difference is related to the nature of the particular auditory and visual stimuli used.

Acoustic Stimulation↗

PubMed2000

A comparison of visual and auditory motion processing in human cerebral cortex.

Visual and auditory motion information can be used together to provide complementary information about the movement of objects. To investigate the neural substrates of such cross-modal integration, functional magnetic resonance imaging was used to assess brain activation while subjects performed separate visual and auditory motion discrimination tasks. Areas of unimodal activation included the primary and/or early sensory cortex for each modality plus additional sites extending toward parietal cortex. Areas conjointly activated by both tasks included lateral parietal cortex, lateral frontal cortex, anterior midline and anterior insular cortex. The parietal site encompassed distinct, but partially overlapping, zones of activation in or near the intraparietal sulcus (IPS). A subsequent task requiring an explicit cross-modal speed comparison revealed several foci of enhanced activity relative to the unimodal tasks. These included the IPS, anterior midline, and anterior insula but not frontal cortex. During the unimodal auditory motion task, portions of the dorsal visual motion system showed signals depressed below resting baseline. Thus, interactions between the two systems involved either enhancement or suppression depending on the stimuli present and the nature of the perceptual task. Together, these results identify human cortical regions involved in polysensory integration and the attentional selection of cross-modal motion information.

Acoustic Stimulation↗