Showing papers on "Temporal cortex published in 1996"
TL;DR: This study studied the functional anatomy of semantic processing by using positron-emission tomography to contrast activity during two semantic tasks (probing knowledge of associations between concepts, and knowledge of the visual attributes of these concepts), performed either with words or with pictures.
Abstract: THE relationship between the semantic processing of words and of pictures is a matter of debate among cognitive scientists1,2. We studied the functional anatomy of such processing by using positron-emission tomography (PET). We contrasted activity during two semantic tasks (probing knowledge of associations between concepts, and knowledge of the visual attributes of these concepts) and a baseline task (discrimination of physical stimulus size), performed either with words or with pictures. Modality-specific activations unrelated to semantic processing occurred in the left inferior parietal lobule for words, and the right middle occipital gyrus for pictures. A semantic network common to both words and pictures extended from the left superior occipital gyrus through the middle and inferior temporal cortex to the inferior frontal gyrus. A picture-specific activation related to semantic tasks occurred in the left posterior inferior temporal sulcus, and word-specific activations related to semantic tasks were localized to the left superior temporal sulcus, left anterior middle temporal gyrus, and left inferior frontal sulcus. Thus semantic tasks activate a distributed semantic processing system shared by both words and pictures, with a few specific areas differentially active for either words or pictures.
1,151 citations
TL;DR: The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence, and the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes.
Abstract: The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence. The volume of neural tissue activated (number of voxels) during sentence comprehension was measured with echo-planar functional magnetic resonance imaging. The modulation of the volume of activation by sentence complexity was observed in a network of four areas: the classical left-hemisphere language areas (the left laterosuperior temporal cortex, or Wernicke's area, and the left inferior frontal gyrus, or Broca's area) and their homologous right-hemisphere areas, although the right areas had much smaller volumes of activation than did the left areas. These findings generally indicate that the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes.
1,045 citations
TL;DR: Three commonly observed neuronal effects in memory-demanding tasks are repetition suppression, enhancement, and delay activity, which appear to be an intrinsic property of visual cortical areas such as inferior temporal cortex and is thought to be important for perceptual learning and priming.
Abstract: Recent studies show that neuronal mechanisms for learning and memory both dynamically modulate and permanently alter the representations of visual stimuli in the adult monkey cortex. Three commonly observed neuronal effects in memory-demanding tasks are repetition suppression, enhancement, and delay activity. In repetition suppression, repeated experience with the same visual stimulus leads to both short- and long-term suppression of neuronal responses in subpopulations of visual neurons. Enhancement works in an opposite fashion, in that neuronal responses are enhanced for objects with learned behavioral relevance. Delay activity is found in tasks in which animals are required to actively hold specific information “on-line” for short periods. Repetition suppression appears to be an intrinsic property of visual cortical areas such as inferior temporal cortex and is thought to be important for perceptual learning and priming. By contrast, enhancement and delay activity may depend on feedback to temporal cortex from prefrontal cortex and are thought to be important for working memory. All of these mnemonic effects on neuronal responses bias the competitive interactions that take place between stimulus representations in the cortex when there is more than one stimulus in the visual field. As a result, memory will often determine the winner of these competitions and, thus, will determine which stimulus is attended.
1,025 citations
TL;DR: The results suggest that emotions associated with the PTSD symptomatic state are mediated by the limbic and paralimbic systems within the right hemisphere.
Abstract: Background: Previous studies have used symptom provocation and positron emission tomography to delineate the brain systems that mediate various anxiety states. Using an analogous approach, the goal of this study was to measure regional cerebral blood flow changes associated with posttraumatic stress disorder (PTSD) symptoms. Methods: Eight patients with PTSD, screened as physiologically responsive to a script-driven imagery symptom provocation paradigm, were exposed sequentially to audiotaped traumatic and neutral scripts in conjunction with positron emission tomography. Heart rate and subjective measures of emotional state were obtained for each condition. Statistical mapping techniques were used to determine locations of significant brain activation. Results: Increases in normalized blood flow were found for the traumatic as compared with control conditions in rightsided limbic, paralimbic, and visual areas; decreases were found in left inferior frontal and middle temporal cortex. Conclusions: The results suggest that emotions associated with the PTSD symptomatic state are mediated by the limbic and paralimbic systems within the right hemisphere. Activation of visual cortex may correspond to the visual component of PTSD reexperiencing phenomena.
956 citations
TL;DR: The results demonstrated that the perception of scripts of goal-directed hand action implicates the cortex in the intraparietal sulcus and the caudal part of the superior temporal sulcus, both in the left hemisphere.
Abstract: To explore the extent to which functional systems within the human posterior parietal cortex and the superior temporal sulcus are involved in the perception of action, we measured cerebral metabolic activity in human subjects by positron emission tomography during the perception of simulations of biological motion with point-light displays. The experimental design involved comparisons of activity during the perception of goal-directed hand action, whole body motion, object motion, and random motion. The results demonstrated that the perception of scripts of goal-directed hand action implicates the cortex in the intraparietal sulcus and the caudal part of the superior temporal sulcus, both in the left hemisphere. By contrast, the rostrocaudal part of the right superior temporal sulcus and adjacent temporal cortex, and limbic structures such as the amygdala, are involved in the perception of signs conveyed by expressive body movements.
720 citations
TL;DR: The left inferolateral temporal cortex and the posterior part of the inferior parietal lobe were only activated by word retrieval, particularly verbs, and it is proposed that these activated regions reflect access to semantic fields.
Abstract: PET activation studies identify significant local changes in regional cerebral blood flow (rCBF) in contrasts of behavioural tasks with control states, and these local changes identify net changes in local synaptic activity. A number of studies on word retrieval have all demonstrated left frontal (dorsolateral and medial) involvement in the task. However, there have been differences in the responses observed in the left temporal lobe, with variously a deactivation (significant decrease in rCBF), no response and an activation (significant increase in rCBF). In the four studies described here, we have examined word (verbs and nouns) retrieval contrasted with a number of different control states. The studies confirmed extensive activation of the left dorsolateral prefrontal cortex and, medially, the anterior cingulate cortex and the supplementary motor area (SMA). Activations of the left posterior temporal lobe and the inferior parietal lobe were consistently demonstrated when word retrieval was contrasted with a rest state. Contrasts with other single word tasks controlled out the activation in the perisylvian part of the left posterior temporal lobe, suggesting a role for this region in lexical processing. The left inferolateral temporal cortex and the posterior part of the inferior parietal lobe were only activated by word retrieval, particularly verbs. It is proposed that these activated regions reflect access to semantic fields.
626 citations
TL;DR: It is shown that cerebral erythropoietin and its receptor are expressed in the brain of primates as they are in rodents, and that, at least in mice, primary astrocytes are a source of cerebral eriespheric expression which can be up‐regulated by reduced oxygenation.
Abstract: The haematopoietic growth factor erythropoietin is the primary regulator of mammalian erythropoiesis and is produced by the kidney and the liver in an oxygen-dependent manner. We and others have recently demonstrated erythropoietin gene expression in the rodent brain. In this work, we show that cerebral erythropoietin gene expression is not restricted to rodents but occurs also in the primate brain. Erythropoietin mRNA was detected in biopsies from the human hippocampus, amygdala and temporal cortex and in various brain areas of the monkey Macaca mulatta. Exposure to a low level of oxygen led to elevated erythropoietin mRNA levels in the monkey brain, as did anaemia in the mouse brain. In addition, erythropoietin receptor mRNA was detected in all brain biopsies tested from man, monkey and mouse. Analysis of primary cerebral cells isolated from newborn mice revealed that astrocytes, but not microglia cells, expressed erythropoietin. When incubated at 1% oxygen, astrocytes showed >100-fold time-dependent erythropoietin mRNA accumulation, as measured with the quantitative reverse transcription-polymerase chain reaction. The specificity of hypoxic gene induction in these cells was confirmed by quantitative Northern blot analysis showing hypoxic up-regulation of mRNA encoding the vascular endothelial growth factor, but not of other genes. These findings demonstrate that erythropoietin and its receptor are expressed in the brain of primates as they are in rodents, and that, at least in mice, primary astrocytes are a source of cerebral erythropoietin expression which can be up-regulated by reduced oxygenation.
549 citations
TL;DR: In this article, the authors investigated cerebral blood flow changes associated with the processing of speech using positron emission tomography (PET) and found increased CBF in the left frontal lobe, close to the border between Broca's area and the motor cortex.
Abstract: Positron emission tomography was used to investigate cerebral blood flow (CBF) changes associated with the processing of speech. In a first experiment normal right-handed volunteers were scanned under two conditions that required phonetic processing (discrimination of final consonants and phoneme monitoring), and one baseline condition of passive listening. Analysis was carried out by paired-image subtraction, with MRI overlay for anatomical localization. Comparison of each phonetic condition with the baseline condition revealed increased CBF in the left frontal lobe, close to the border between Broca's area and the motor cortex, and in a left parietal region. A second experiment showed that this area was not activated by a semantic judgment task. Reanalysis of data from an earlier study, in which various baseline conditions were used, confirmed that this region of left frontal cortex is consistently involved in phonetic tasks. The findings support a model whereby articulatory processes involving a portion of Broca's area are important when phonetic segments must be extracted and manipulated, whereas left posterior temporal cortex is involved in perceptual analysis of speech.
427 citations
TL;DR: It is concluded that cholinergic neuron integrity can be monitored in living AD and PD patients, and that it is not so devastated in vivo as suggested by postmortem choline acetylransferase activity.
Abstract: To map presynaptic cholinergic terminal densities in normal aging (n = 36), Alzheimer's disease (AD) (n = 22), and Parkinson's disease (PD) (n = 15), we performed single-photon emission computed tomography using [123I]iodobenzovesamicol (IBVM), an in vivo marker of the vesicular acetylcholine transporter. We used coregistered positron emission tomography with [18F]fluorodeoxyglucose for metabolic assessment and coregistered magnetic resonance imaging for atrophy assessment. In controls (age, 22-91 years), cortical IBVM binding declined only 3.7% per decade. In AD, cortical binding correlated inversely with dementia severity. In mild dementia, binding differed according to age of onset, but metabolism did not. With an onset age of less than 65 years, binding was reduced severely throughout the entire cerebral cortex and hippocampus (about 30%), but with an onset age of 65 years or more, binding reductions were restricted to temporal cortex and hippocampus. In PD without dementia, binding was reduced only in parietal and occipital cortex, but demented PD subjects had extensive cortical binding decreases similar to early-onset AD. We conclude that cholinergic neuron integrity can be monitored in living AD and PD patients, and that it is not so devastated in vivo as suggested by postmortem choline acetyltransferase activity (50-80%).
362 citations
TL;DR: Frontal lobe degenerative dementias, the second largest degenerative dementia group after Alzheimer's disease, is dominated by frontal lobe degeneration of non-Alzheimer type.
Abstract: Frontal lobe degenerative dementias, the second largest degenerative dementia group after Alzheimer's disease, is dominated by frontal lobe degeneration of non-Alzheimer type. It is classified in a group also containing Pick's disease, progressive aphasia and dementia in motor neuron disease. Frontal lobe degeneration of non-Alzheimer type is clinically marked by frontal lobe symptoms and frontotemporal reduction of blood flow. From a histopathological point of view it is characterized by gliosis, microvacuolation, neuronal atrophy-loss and 40–50% loss of synapses in three superficial cortical laminae of the frontal convexity and anterior temporal cortex, while the deeper laminae are little or not changed. The structural changes of Alzheimer's disease including amyloid, Levy body dementia and Pick's disease are entirely lacking. A strong heredity points to a genetic cause as yet undefined.
339 citations
TL;DR: Findings suggest a pathway that is commonly used during the episodic retrieval of picture and word stimuli under these conditions, and many areas in this pathway overlap with areas previously activated by a different set of retrieval tasks using stem-cued recall, demonstrating their generality.
Abstract: Functional neuroimaging with positron emission tomography was used to study brain areas activated during memory retrieval. Subjects (n = 15) recalled items from a recent study episode (episodic memory) during two paired-associate recall tasks. The tasks differed in that PICTURE RECALL required pictorial retrieval, whereas AUDITORY WORD RECALL required word retrieval. Word REPETITION and REST served as two reference tasks. Comparing recall with repetition revealed the following observations. (1) Right anterior prefrontal activation (similar to that seen in several previous experiments), in addition to bilateral frontal-opercular and anterior cingulate activations. (2) An anterior subdivision of medial frontal cortex [pre-supplementary motor area (SMA)] was activated, which could be dissociated from a more posterior area (SMA proper). (3) Parietal areas were activated, including a posterior medial area near precuneus, that could be dissociated from an anterior parietal area that was deactivated. (4) Multiple medial and lateral cerebellar areas were activated. Comparing recall with rest revealed similar activations, except right prefrontal activation was minimal and activations related to motor and auditory demands became apparent (e.g., bilateral motor and temporal cortex). Directly comparing picture recall with auditory word recall revealed few notable activations. Taken together, these findings suggest a pathway that is commonly used during the episodic retrieval of picture and word stimuli under these conditions. Many areas in this pathway overlap with areas previously activated by a different set of retrieval tasks using stem-cued recall, demonstrating their generality. Examination of activations within individual subjects in relation to structural magnetic resonance images provided an-atomic information about the location of these activations. Such data, when combined with the dissociations between functional areas, provide an increasingly detailed picture of the brain pathways involved in episodic retrieval tasks.
TL;DR: A cortical system for "pragmatic' manipulation of simple neutral objects is defined in this functional-anatomic study and consistent anatomic landmarks from MRI scans could be identified to locate sensorimotor, ventral SMA, and SII blood flow increases.
Abstract: The functional anatomy of reaching and grasping simple objects was determined in nine healthy subjects with positron emission tomography imaging of regional cerebral blood flow (rCBF). In a prehension (grasping) task, subjects reached and grasped illuminated cylindrical objects with their right hand. In a pointing task, subjects reached and pointed over the same targets. In a control condition subjects looked at the targets. Both movement tasks increased activity in a distributed set of cortical and subcortical sites: contralateral motor, premotor, ventral supplementary motor area (SMA), cingulate, superior parietal, and dorsal occipital cortex. Cortical areas including cuneate and dorsal occipital cortex were more extensively activated than ventral occipital or temporal pathways. The left parietal operculum (putative Sll) was recruited during grasping but not pointing. Blood flow changes were individually localized with respect to local cortical anatomy using sulcal landmarks. Consistent anatomic landmarks from MRI scans could be identified to locate sensorimotor, ventral SMA, and Sll blood flow increases. The time required to complete individual movements and the amount of movement made during imaging correlated positively with the magnitude of rCBF increases during grasping in the contralateral inferior sensorimotor, cingulate, and ipsilateral inferior temporal cortex, and bilateral anterior cerebellum. This functionalanatomic study defines a cortical system for "pragmatic" manipulation of simple neutral objects.
TL;DR: Results provide evidence that the so-called dorsal route known to process visuospatial features can be recruited by auditory verbal stimuli and confirm previous reports indicating that some mental imagery tasks may not involve any significant participation of early visual areas.
Abstract: Positron emission tomography (PET) was used to monitor regional cerebral blood flow variations while subjects were constructing mental images of objects made of three-dimensional cube assemblies from auditorily presented instructions. This spatial mental imagery task was contrasted with both passive listening (LIST) of phonetically matched nonspatial word lists and a silent rest (REST) condition. All three tasks were performed in total darkness. Mental construction (CONS) specifically activated a bilateral occipitoparietal‐frontal network, including the superior occipital cortex, the inferior parietal cortex, and the premotor cortex. The right inferior temporal cortex also was activated specifically during this condition, and no activation of the primary visual areas was observed. Bilateral superior and middle temporal cortex activations were common to CONS and LIST tasks when both were compared with the REST condition. These results provide evidence that the so-called dorsal route known to process visuospatial features can be recruited by auditory verbal stimuli. They also confirm previous reports indicating that some mental imagery tasks may not involve any significant participation of early visual areas.
TL;DR: In this paper, the neural correlates of inner speech and of auditory verbal imagery were examined in normal volunteers, using positron emission tomography (PET) in order to examine the neural networks associated with these two tasks.
Abstract: The neural correlates of inner speech and of auditory verbal imagery were examined in normal volunteers, using positron emission tomography (PET). Subjects were shown single words which they used to generate short, stereotyped sentences without speaking. In an inner speech task, sentences were silently articulated, while in an auditory verbal imagery condition, subjects imagined sentences being spoken to them in an another person's voice. Inner speech was associated with increased activity in the left inferior frontal gyrus. Auditory verbal imagery was associated with increases in the same region, and in the left premotor cortex, the supplementary motor area and the left temporal cortex. The data suggest that the silent articulation of sentences involves activity in an area concerned with speech generation, while imagining speech is associated with additional activity in regions associated with speech perception.
TL;DR: In this paper, the authors examined the neural correlates of verbal self-monitoring by measuring the response to alterations in auditory verbal feedback while subjects read aloud and found that self-and externally generated speech are processed in similar regions of temporal cortex, and the monitoring of self-generated speech involves the temporal cortex bilaterally, in areas associated with the processing of speech which has been generated externally.
Abstract: Summary The neural correlates of verbal self-monitoring were examined by measuring the response to alterations in auditory verbal feedback while subjects read aloud. Six normal subjects were studied with PET, using H215O as a tracer of regional CBF. There was no difference between the temporal cortical response to reading aloud (and hearing one's own speech) and reading silently while hearing the words spoken by someone else. Distortion of subjects' speech (by pitch elevation) while they read aloud led to a bilateral activation of lateral temporal cortex, with a greater response on the right side than the left. A similar pattern of activation was evident when subjects read aloud, but the words they heard were spoken by someone else. These data suggest that (i) self- and externally generated speech are processed in similar regions of temporal cortex, and (ii) the monitoring of self-generated speech involves the temporal cortex bilaterally, in areas associated with the processing of speech which has been generated externally.
TL;DR: The hypothesis that an aborted attempt of terminally differentiated neurones to re-enter the cell cycle might be a critical event in the pathology of Alzheimer's disease is supported.
Abstract: Recent evidence indicates that an impairment of neuronal adaptive and reparative processes might be a key feature of the pathomechanism of Alzheimer's disease. Aberrations in the reparative neuronal response are likely to result from alterations of intracellular signal transduction cascades. As a consequence of abnormal intracellular signalling, the activation of those molecular events might be triggered in neurones which, in dividing cells, would lead to cellular transformation. In the present study, changes in the expression of the cyclin-dependent kinase inhibitor p16, a regulator of the orderly progression through the cell cycle, were investigated by immunocytochemical methods in the temporal cortex of patients with Alzheimer's disease. Both neurofibrillary tangles and neuritic components of plaques showed strong p16 immunoreactivity. These findings support the hypothesis that an aborted attempt of terminally differentiated neurones to re-enter the cell cycle might be a critical event in the pathology of Alzheimer's disease.
TL;DR: The ability of inferotemporal neurons to represent association between picture pairs was lost after the lesion of entorhinal and perirhinal cortex, most likely through disruption of backward neural signals to the inferotmporal neurons, while the ability of the neurons to respond to a particular visual stimulus was left intact.
Abstract: Functional roles of the cortical backward signal in long-term memory formation were studied in monkeys performing a visual pair-association task. Before the monkeys learned the task, the anterior commissure was transected, disconnecting the anterior temporal cortex of each hemisphere. After training with 12 pairs of pictures, single units were recorded from the inferotemporal cortex of the monkeys as the control. By injecting a grid of ibotenic acid, we unilaterally lesioned the entorhinal and perirhinal cortex, which provides massive direct and indirect backward projections ipsilaterally to the inferotemporal cortex. After the lesion, the monkeys fixated the cue stimulus normally, relearned the preoperatively learned set (set A), and learned a new set (set B) of paired associates. Then, single units were recorded from the same area as for the prelesion control. We found that (i) in spite of the lesion, the sampled neurons responded strongly and selectively to both the set A and set B patterns and (ii) the paired associates elicited significantly correlated responses in the control neurons before the lesion but not in the cells tested after the lesion, either for set A or set B stimuli. We conclude that the ability of inferotemporal neurons to represent association between picture pairs was lost after the lesion of entorhinal and perirhinal cortex, most likely through disruption of backward neural signals to the inferotemporal neurons, while the ability of the neurons to respond to a particular visual stimulus was left intact.
TL;DR: The acquired data provide exquisite delineation of 5-HT1A receptors in brain, with the ratio of radioactivity uptake in receptor-rich regions, such as medial temporal cortex, to that in receptors-devoid cerebellum reaching 25 by 60 min after radioligand injection.
TL;DR: The representation of emotional faces over a delay period, compared to either the nonemotional or the fixation condition, was associated with significant activation in the left ventral prefrontal cortex, the left anterior cingulate cortex, and the right fusiform gyrus.
TL;DR: Despite the association of a hydrophobic fragment of NACP with senile plaques, the data suggest that the precursor itself is not a significant component of plaques and NACP synthesis is not substantially altered in AD, and the protein is an abundant component of synaptic regions prone to degeneration in AD.
Abstract: A novel and highly conserved presynaptic protein has been independently described in rodents (synuclein/SYN-1), songbirds (synelfin), and humans (the precursor protein of the non-A beta component of senile plaques, NACP); a fragment of the latter has been detected in senile plaques in Alzheimer's disease (AD). We characterized the expression of NACP in human AD and non-AD brain. A subcellular fractionation study demonstrated that NACP was mainly localized to cytosolic fractions of human temporal cortex. NACP was also detectable in various membrane and vesicular fractions, suggesting that the protein was associated with membrane structures including synaptic vesicles. Pericellular immunostaining of the neuropil was observed in neocortical and limbic regions, supporting a synaptic localization. Senile plaques in AD brains were not immunoreactive, and confocal microscopy suggested a loss of NACP immunoreactivity in cored plaques. No difference was found in the amount of protein in AD and control frontal cortex, as measured by immunoblotting. PCR analysis showed that the full-length mRNA product was the major splice form in both AD and control human brains. Thus, despite the association of a hydrophobic fragment of NACP with senile plaques, our data suggest that the precursor itself is not a significant component of plaques and NACP synthesis is not substantially altered in AD. Nevertheless, the protein is an abundant component of synaptic regions prone to degeneration in AD, and may have a role in the expression or advancement of the disease.
TL;DR: It is concluded that low BMI correlates best and specifically with MTC atrophy, which supports a connection between limbic system damage and low body weight in AD.
Abstract: There are reports of weight loss and low body mass index (BMI) in patients with AD. The mesial temporal cortex (MTC) is involved in feeding behavior and memory and is preferentially involved in AD. We studied 74 subjects, including 58 AD patients and 16 control subjects, to determine whether BMI is associated with atrophy of the MTC or other brain regions. We used MRI morphometric analysis to provide measures of regional brain atrophy. AD patients had significant brain atrophy in all measured brain regions, except the white matter, compared with normal control subjects. The MTC was the only brain region significantly associated with BMI in AD patients (r = 0.39, p = 0.003). Multiple-regression analysis indicated that addition of brain regions other than the MTC to the model did not significantly add to the prediction of BMI. We conclude that low BMI correlates best and specifically with MTC atrophy. This finding supports a connection between limbic system damage and low body weight in AD.
TL;DR: The data are interpreted to suggest that when subjects use cognitive strategies of semantic processing and rote-rehearsal to learn words, they invoke discrete regions of the left prefrontal cortex which leads to a neurophysiological memory trace which can be used to guide subsequent memory retrieval.
TL;DR: Findings confirm that, in human subjects, memory for object features is mediated by a distributed system that includes ventral prestriate cortex and both anterior and posterior regions of the inferior temporal gyrus and that memory for the locations of objects appears to be mediated by an anatomically distinct system.
Abstract: Regional cerebral blood flow was measured with positron-emission tomography during two encoding and two retrieval tasks that were designed to compare memory for object features with memory for object locations. Bilateral increases in regional cerebral blood flow were observed in both anterior and posterior regions of inferior temporal cortex and in ventral regions of prestriate cortex, when the condition that required retrieval of object locations was subtracted from the condition that required retrieval of object features. During encoding, these changes were less pronounced and were restricted to the left inferior temporal cortex and right ventral prestriate cortex. In contrast, both encoding and retrieval of object location were associated with bilateral changes in dorsal prestriate and posterior parietal cortex. Finally, the two encoding conditions activated left frontal lobe regions preferentially, whereas the two retrieval conditions activated right frontal lobe regions. These findings confirm that, in human subjects, memory for object features is mediated by a distributed system that includes ventral prestriate cortex and both anterior and posterior regions of the inferior temporal gyrus. In contrast, memory for the locations of objects appears to be mediated by an anatomically distinct system that includes more dorsal regions of prestriate cortex and posterior regions of the parietal lobe.
TL;DR: Regional cerebral blood flow was measured using positron emission tomography during eyeblink conditioning in young adults to suggest that the same brain regions in animals and humans mediate multiple forms of associative learning that give meaning to a previously neutral stimulus.
Abstract: Regional cerebral blood flow (rCBF) was measured using positron emission tomography during eyeblink conditioning in young adults. Subjects were scanned in three experimental conditions: delay conditioning, in which binaural tones preceded air puffs to the right eye by 400 msec; pseudoconditioning, in which presentations of tone and air puff stimuli were not correlated in time; and fixation rest, which served as a baseline control. Compared with fixation, pseudoconditioning produced rCBF increases in frontal and temporal cortex, basal ganglia, left hippocampal formation, and pons. Learning-specific activations were observed in conditioning as compared with pseudoconditioning in bilateral frontal cortex, left thalamus, right medial hippocampal formation, left lingual gyrus, pons, and bilateral cerebellum; decreases in rCBF were observed for bilateral temporal cortex, and in the right hemisphere in putamen, cerebellum, and the lateral aspect of hippocampal formation. Blood flow increased as the level of learning increased in the left hemisphere in caudate, hippocampal formation, fusiform gyrus, and cerebellum, and in right temporal cortex and pons. In contrast, activation in left frontal cortex decreased as learning increased. These functional imaging results implicate many of the same structures identified by previous lesion and recording studies of eyeblink conditioning in animals and humans and suggest that the same brain regions in animals and humans mediate multiple forms of associative learning that give meaning to a previously neutral stimulus.
TL;DR: In situ hybridization using an antisense cRNA-probe demonstrated that the melatonin receptor mRNA is localized in the cerebellar granule cells, and a quite widespread distribution of the transcript, although expressed at very low levels.
TL;DR: Neural activity during the delay period of spatial delayed response (DR) and delayed matching (DM) tasks was investigated by positron emission tomography and activation of a distributed cortical system was activated in each condition.
Abstract: Neural activity during the delay period of spatial delayed response (DR) and delayed matching (DM) tasks was investigated by positron emission tomography A distributed cortical system was activated in each condition. The bilateral dorsolateral prefrontal cortex (DLPFC) was activated in the delay period of both tasks; activation was of higher significance on the right in the DR task and the left in the DM task, and extended to the anterolateral prefrontal cortex in the DM condition. Active representation of spatial location in the DR task was associated with co-activation of the medial and lateral parietal cortex and the extrastriate visual cortex. Active representation of shape in the DM task was associated with co-activation of the medial and lateral parietal cortex and the inferior temporal cortex. Response-related activity was observed in both tasks. Activation of anterior cingulate, inferior frontal, lateral premotor and rostral inferior parietal cortex was observed in the DR condition, a task characterized by preparation of a movement to a predetermined location. In contrast, preparation to move to an undetermined location in the DM task was associated with activation predominantly in rostral SMA.
TL;DR: Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit of VNS, consistent with the role of theThalamus as a generator and modulator of cerebral activity.
Abstract: OBJECTIVE : To determine the central areas of activation by vagal nerve stimulation (VNS) in epilepsy. VNS is a promising neurosurgical method for treating patients with partial and secondary generalized epilepsy. The anti-epileptic mechanism of action from VNS is not well understood. METHODS : We performed H 2 15 O PET blood flow functional imaging on three patients with epilepsy in a vagal nerve stimulation study (E04 Protocol with Cyberonics). The three patients included two that had previous epilepsy surgery but continued to have frequent seizures. Seizure onset was frontal in two patients and bitemporal in the third patient. Twelve PET scans per subject were acquired every 10 minutes with a Siemens 953/A scanner. In 6 stimulus scans, VNS was activated for 60 seconds (2 mA, 30 Hz) commensurate with isotope injection. In 6 control scans no VNS was administered. No clinical seizures were present during any scan. Three way ANOVA with linear contrasts (subject, task, repetition) of coregistered images identified significant treatment effects. RESULTS : The difference between PET with VNS and without revealed that left VNS activated right thalamus (P<0.0006), right posterior temporal cortex (P<0.0003), left putamen (P<0.0002), and left inferior cerebellum (P<0.0009). CONCLUSIONS : VNS causes activation of several central areas including contralateral thalamus. Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit, consistent with the role of the thalamus as a generator and modulator of cerebral activity.
TL;DR: The finding that these cells are among the most vulnerable types of GABAergic interneurons in the epileptogenic temporal cortex indicates that they might be of great functional importance, since the axon terminals of chandelier cells are likely to exert powerful regulation of impulse generation in cortical pyramidal cells.
Abstract: Immunocytochemical methods were used to study alterations in inhibitory neuronal circuits in human neocortex resected during surgical treatment of intractable temporal epilepsy associated or not with brain tumours. The epileptogenic cortex was characterized and divided into spiking or non-spiking zones by intraoperative electrocorticography (ECOG). The resected cortex was cut into blocks, sectioned and stained immunocytochemically for visualization of glutamic acid decarboxylase (GAD), the calcium-binding protein, parvalbumin (PV) and glial fibrillary acidic protein (GFAP). A variety of alterations in cortical neuronal circuits as revealed by immunocytochemical and histological methods were found. Similar alterations in inhibitory neuronal circuits appear to occur independently of the primary epileptogenic site and pathology associated with epilepsy, which suggests that there is possibly a common basic underlying mechanism that leads to seizure activity. These changes were apparently unrelated to ECOG findings at surgery, which bring into question the value of the use of interictal epileptic discharges recorded by ECOG to guide cortical resections. The most conspicuous and common change was the loss of chandelier cells. The finding that these cells are among the most vulnerable types of GABAergic interneurons in the epileptogenic temporal cortex indicates that they might be of great functional importance, since the axon terminals of chandelier cells are likely to exert powerful regulation of impulse generation in cortical pyramidal cells. Therefore, these cells might represent a key component in the aetiology of human epilepsy.
TL;DR: Two interconnected networks are distinguished that are associated with the inferotemporal cortex and includes areas of the ventral bank and fundus of the superior temporal sulcus, lateral FEF and ventral prestriate cortex, which emphasizes central vision, small accades and form recognition.