The neural substrate of memory impairment demonstrated by the intracarotid amobarbital procedure

The intracarotid amobarbital sodium (Amytal) procedure (IAP) was performed for 46 patients with temporal lobe epilepsy (21 with left seizure foci; 25 with right seizure foci). After anteromedial temporal lobectomy, neuronal densities were established for hippocampal subfields CA1, CA2, and CA3; the hilum; and the dentate granule cell layer. Intracarotid amobarbital procedure memory results were related to CA3 neuronal loss only. Patients who did not demonstrate memory after injection contralateral to the seizure focus had significantly fewer cells in CA3 than patients who did. Additionally, a significant correlation was observed between the intracarotid amobarbital procedure memory examination raw score after injection contralateral to the seizure focus and CA3 cell density. Using chi 2 analysis, significant differences were documented in the frequency with which memory was demonstrated after injection contralateral to the seizure focus for groups of patients classified by degree of CA3 neuronal loss. This finding supports prior research showing subfield specificity in some memory processes.     

The neural substrate of gesture recognition

Previous studies have linked action recognition with a particular pool of neurons located in the ventral premotor cortex, the posterior parietal cortex and the superior temporal sulcus (the mirror neuron system). However, it is still unclear if transitive and intransitive gestures share the same neural substrates during action-recognition processes. In the present study, we used event-related functional magnetic resonance imaging (fMRI) to assess the cortical areas active during recognition of pantomimed transitive actions, intransitive gestures, and meaningless control actions. Perception of all types of gestures engaged the right pre-supplementary motor area (pre-SMA), and bilaterally in the posterior superior temporal cortex, the posterior parietal cortex, occipitotemporal regions and visual cortices. Activation of the posterior superior temporal sulcus/superior temporal gyrus region was found in both hemispheres during recognition of transitive and intransitive gestures, and in the right hemisphere during the control condition; the middle temporal gyrus showed activation in the left hemisphere when subjects recognized transitive and intransitive gestures; activation of the left inferior parietal lobe and intraparietal sulcus (IPS) was mainly observed in the left hemisphere during recognition of the three conditions. The most striking finding was the greater activation of the left inferior frontal gyrus (IFG) during recognition of intransitive actions. Results show that a similar neural substrate, albeit, with a distinct engagement underlies the cognitive processing of transitive and intransitive gestures recognition. These findings suggest that selective disruptions in these circuits may lead to distinct clinical deficits.     

The neural association between arithmetic and basic numerical processing depends on arithmetic problem size and not chronological age

The intraparietal sulcus (IPS) is thought to be an important region for basic number processing (e.g. symbol-quantity associations) and arithmetic (e.g. addition). Evidence for shared circuitry within the IPS is largely based on comparisons across studies, and little research has investigated number processing and arithmetic in the same individuals. It is also unclear how the neural overlap between number processing and arithmetic is influenced by age and arithmetic problem difficulty. This study investigated these unresolved questions by examining basic number processing (symbol-quantity matching) and arithmetic (addition) networks in 26 adults and 42 children. Number processing and arithmetic elicited overlapping activity in the IPS in children and adults, however, the overlap was influenced by arithmetic problem size (i.e. which modulated the need to use procedural strategies). The IPS was recruited for number processing, and for arithmetic problems more likely to be solved using procedural strategies. We also found that the overlap between number processing and small-problem addition in children was comparable to the overlap between number processing and large-problem addition in adults. This finding suggests that the association between number processing and arithmetic in the IPS is related to the cognitive operation being performed rather than age.     

The neural substrate of picture naming.

A PET study of 10 normal males was carried out using the bolus H215O intravenous injection technique to examine the effects of picture naming and semantic judgment on blood flow. In a series of conditions, subjects (1) passively viewed flashing plus signs, (2) noted the occurrence of abstract patterns, (3) named animal pictures, or (4) carried out a semantic judgment on animal pictures. Anticipatory scans were carried out after the subjects were presented with the instructions but before they began the cognitive task, as they were passively viewing plus signs. Our results serve to clarify a number of current controversies regarding the neural substrate of picture naming. The results indicate that the fusiform gyrus is unlikely to be the region where low-level perceptual processing such as shape analysis is undertaken. In fact, our evidence suggests that activation of the fusiform gyrus is most likely related to visual perceptual semantic processing. In addition, the inferior/middle frontal lobe activity observed while performing the picture naming and semantic judgment tasks does not appear to be due to the effects of anticipation or preparation. Furthermore, there appears to be a set of regions (a semantic network) that becomes activated regardless of whether the subjects perform a picture naming or semantic judgment task. Finally, picture naming of animals did not activate either parietal regions or anterior inferior left temporal regions, regardless of what subtraction baseline was used.     

The neural substrate of orientation working memory

We have used positron emission tomography (PET) to identify the neural substrate of two major cognitive components of working memory (WM), maintenance and manipulation of a single elementary visual attribute, i.e., the orientation of a grating presented in central vision. This approach allowed us to equate difficulty across tasks and prevented subjects from using verbal strategies or vestibular cues. Maintenance of orientations involved a distributed fronto-parietal network, that is, left and right lateral superior frontal sulcus (SFSl), bilateral ventrolateral prefrontal cortex (VLPFC), bilateral precuneus, and right superior parietal lobe (SPL). A more medial superior frontal sulcus region (SFSm) was identified as being instrumental in the manipulative operation of updating orientations retained in the WM. Functional connectivity analysis revealed that orientation WM relies on a coordinated interaction between frontal and parietal regions. In general, the current findings confirm the distinction between maintenance and manipulative processes, highlight the functional heterogeneity in the prefrontal cortex (PFC), and suggest a more dynamic view of WM as a process requiring the coordinated interaction of anatomically distinct brain areas.     

Information complexity of neural networks.

This paper studies the question of lower bounds on the number of neurons and examples necessary to program a given task into feed forward neural networks. We introduce the notion of information complexity of a network to complement that of neural complexity. Neural complexity deals with lower bounds for neural resources (numbers of neurons) needed by a network to perform a given task within a given tolerance. Information complexity measures lower bounds for the information (i.e. number of examples) needed about the desired input-output function. We study the interaction of the two complexities, and so lower bounds for the complexity of building and then programming feed-forward nets for given tasks. We show something unexpected a priori--the interaction of the two can be simply bounded, so that they can be studied essentially independently. We construct radial basis function (RBF) algorithms of order n3 that are information-optimal, and give example applications.     

The nature of the sense of effort and its neural substrate

INTRODUCTION: What are the nature and the neural substrate of voluntary force perception? STATE OF ART: Experimental findings demonstrate that efferent signals related to motor command play a dominant role in perceiving voluntary muscular force. This suggests that voluntary force perception is provided through a sense of effort and not through a sense of intramuscular tension. Nevertheless, experimental data show that the contribution of sensory input to effort awareness must not be dismissed. Sensory signals are not involved in generating a signal of effort but rather in calibrating and modulating its magnitude. Neuroimaging and neuropsychological studies revealed that many cortical structures are activated during tasks of voluntary muscular force perception. PERSPECTIVES AND CONCLUSION: In such tasks, the basal ganglia might support the coherence of cortical activity.     

Analgesia and the neural substrate of reward

All the known strong analgesics have high abuse potential and, conversely, powerful rewards such as self-stimulation and drugs of abuse have analgesic properties. This coincidence of effects suggests that analgesia and reward may be related processes. Two types of analgesia have been described. One type is antinociceptive in that the analgesic reduces the intensity of the sensory input reaching the CNS from nociceptors. Another type of analgesia, sometimes called dissociative analgesia and exemplified by the patient reporting "It hurts but the pain does not bother me," has been described by clinicians. Thus strong analgesics can relieve the suffering without necessarily reducing the sensory intensity of pain. If analgesia and abuse potency are related it should be expected that the neural substrates of analgesia and abuse liability have considerable overlap. This paper discusses evidence that the analgesic effects of morphine and amphetamine in the formalin test are synergistic, and depend on dopaminergic neurotransmission involving the dopamine cells of the ventral tegmental area.     

The neural correlates of mental arithmetic in adolescents: a longitudinal fNIRS study

Background

Arithmetic processing in adults is known to rely on a frontal-parietal network. However, neurocognitive research focusing on the neural and behavioral correlates of arithmetic development has been scarce, even though the acquisition of arithmetic skills is accompanied by changes within the fronto-parietal network of the developing brain. Furthermore, experimental procedures are typically adjusted to constraints of functional magnetic resonance imaging, which may not reflect natural settings in which children and adolescents actually perform arithmetic. Therefore, we investigated the longitudinal neurocognitive development of processes involved in performing the four basic arithmetic operations in 19 adolescents. By using functional near-infrared spectroscopy, we were able to use an ecologically valid task, i.e., a written production paradigm.

Results

A common pattern of activation in the bilateral fronto-parietal network for arithmetic processing was found for all basic arithmetic operations. Moreover, evidence was obtained for decreasing activation during subtraction over the course of 1 year in middle and inferior frontal gyri, and increased activation during addition and multiplication in angular and middle temporal gyri. In the self-paced block design, parietal activation in multiplication and left angular and temporal activation in addition were observed to be higher for simple than for complex blocks, reflecting an inverse effect of arithmetic complexity.

Conclusions

In general, the findings suggest that the brain network for arithmetic processing is already established in 12–14 year-old adolescents, but still undergoes developmental changes.

     

On the node complexity of neural networks

New results are presented for the node complexity of threshold logic circuit implementations of n-input, m-output logic functions. When no restrictions are imposed on the network the node complexity is shown to be . One-hidden-layer networks are shown to have a node complexity of O(2ⁿ + m) and θ(m2ⁿ/[n(n + m)]). Networks with weights restricted to the set {−1, 0, 1} are shown to have a node complexity of , and networks for which fan-in is restricted to 2 are shown to have a node complexity of θ(m2ⁿ/(n + log m)).     

The neural response to changing semantic and perceptual complexity during language processing

Speech comprehension involves processing at different levels of analysis, such as acoustic, phonetic, and lexical. We investigated neural responses to manipulating the difficulty of processing at two of these levels. Twelve subjects underwent positron emission tomographic scanning while making decisions based upon the semantic relatedness between heard nouns. We manipulated perceptual difficulty by presenting either clear or acoustically degraded speech, and semantic difficulty by varying the degree of semantic relatedness between words. Increasing perceptual difficulty was associated with greater activation of the left superior temporal gyrus, an auditory‐perceptual region involved in speech processing. Increasing semantic difficulty was associated with reduced activity in both superior temporal gyri and increased activity within the left angular gyrus, a heteromodal region involved in accessing word meaning. Comparing across all the conditions, we also observed increased activation within the left inferior prefrontal cortex as the complexity of language processing increased. These results demonstrate a flexible system for language processing, where activity within distinct parts of the network is modulated as processing demands change. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Classes of feedforward neural networks and their circuit complexity

This paper aims to place neural networks in the context of boolean circuit complexity. We define appropriate classes of feedforward neural networks with specified fan-in, accuracy of computation and depth and using techniques of communication complexity proceed to show that the classes fit into a well-studied hierarchy of boolean circuits. Results cover both classes of sigmoid activation function networks and linear threshold networks. This provides a much needed theoretical basis for the study of the computational power of feedforward neural networks.     

The goal priority network as a neural substrate of Conscientiousness

Conscientiousness is a personality trait associated with many important life outcomes, but little is known about the mechanisms that underlie it. We investigated its neural correlates using functional connectivity analysis in fMRI, which identifies brain regions that act in synchrony. We tested the hypothesis that a broad network resembling a combination of the salience and ventral attention networks, which we provisionally label the goal priority network (GPN), is a neural correlate of Conscientiousness. Self‐ and peer‐ratings of Conscientiousness were collected in a community sample of adults who underwent a resting‐state fMRI scan (N = 218). An independent components analysis yielded five components that overlapped substantially with the GPN. We examined synchrony within and between these GPN subcomponents. Synchrony within one of the components—mainly comprising regions of anterior insula, dorsal anterior cingulate cortex, and dorsolateral prefrontal cortex—was significantly associated with Conscientiousness. Connectivity between this component and the four other GPN components was also significantly associated with Conscientiousness. Our results support the hypothesis that variation in a network that enables prioritization of multiple goals may be central to Conscientiousness.     

The neural substrate for working memory of tactile surface texture

Fine surface texture is best discriminated by touch, in contrast to macro geometric features like shape. We used functional magnetic resonance imaging and a delayed match‐to‐sample task to investigate the neural substrate for working memory of tactile surface texture. Blindfolded right‐handed males encoded the texture or location of up to four sandpaper stimuli using the dominant or non‐dominant hand. They maintained the information for 10–12 s and then answered whether a probe stimulus matched the memory array. Analyses of variance with the factors Hand, Task, and Load were performed on the estimated percent signal change for the encoding and delay phase. During encoding, contralateral effects of Hand were found in sensorimotor regions, whereas Load effects were observed in bilateral postcentral sulcus (BA2), secondary somatosensory cortex (S2), pre‐SMA, dorsolateral prefrontal cortex (dlPFC), and superior parietal lobule (SPL). During encoding and delay, Task effects (texture > location) were found in central sulcus, S2, pre‐SMA, dlPFC, and SPL. The Task and Load effects found in hand‐ and modality‐specific regions BA2 and S2 indicate involvement of these regions in the tactile encoding and maintenance of fine surface textures. Similar effects in hand‐ and modality‐unspecific areas dlPFC, pre‐SMA and SPL suggest that these regions contribute to the cognitive monitoring required to encode and maintain multiple items. Our findings stress both the particular importance of S2 for the encoding and maintenance of tactile surface texture, as well as the supramodal nature of parieto‐frontal networks involved in cognitive control. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.     

The neural substrate of analogical reasoning: an fMRI study

This study investigated the anatomical substrate of analogical reasoning using functional magnetic resonance imaging. In the study, subjects performed a verbal analogy task (e.g., soldier is to army as drummer is to band) and, to control for activation caused by purely semantic access, a semantic judgment task. Significant activation differences between the verbal analogy and the semantic judgment task were found bilaterally in the prefrontal cortex (right BA 11/BA 47 and left BA45), the fusiform gyrus, and the basal ganglia; left lateralized in the postero-superior temporal gyrus (BA 22) and the (para) hippocampal region; and right lateralized in the anterior cingulate. The role of these areas in analogical reasoning is discussed.     

The neural substrate of orientation short-term memory and resistance to distractor items

We used Positron Emission Tomography to map the neural substrate of human short-term memory for orientation, defined as retaining a single orientation in memory over a long delay, by comparing a successive discrimination task with a 6-s delay to the same task with a brief 0.3 s delay and to an identification control task. Short-term memory engaged the superior parietal lobe bilaterally, the middle occipital gyrus bilaterally and the left dorsolateral prefrontal cortex. In addition, we studied the resistance to a distractor item by comparing the successive discrimination task with long delay, with and without an intervening distractor stimulus. This manipulative process engaged left ventral premotor cortex and left dorsolateral prefrontal cortex. The activation of left dorsolateral prefrontal cortex is interpreted as reflecting co-ordination between task components. These results, combined with those of two previous studies using an identical reduction strategy, underscore the functional heterogeneity in the prefrontal cortex during short-term and working memory.     

The neural correlates of morphological complexity processing: Detecting structure in pseudowords

Morphological complexity is a highly debated issue in visual word recognition. Previous neuroimaging studies have shown that speakers are sensitive to degrees of morphological complexity. Two‐step derived complex words (bridging through bridge_N > bridge_V > bridging) led to more enhanced activation in the left inferior frontal gyrus than their 1‐step derived counterparts (running through run_V > running). However, it remains unclear whether sensitivity to degrees of morphological complexity extends to pseudowords. If this were the case, it would indicate that abstract knowledge of morphological structure is independent of lexicality. We addressed this question by investigating the processing of two sets of pseudowords in German. Both sets contained morphologically viable two‐step derived pseudowords differing in the number of derivational steps required to access an existing lexical representation and therefore the degree of structural analysis expected during processing. Using a 2 × 2 factorial design, we found lexicality effects to be distinct from processing signatures relating to structural analysis in pseudowords. Semantically‐driven processes such as lexical search showed a more frontal distribution while combinatorial processes related to structural analysis engaged more parietal parts of the network. Specifically, more complex pseudowords showed increased activation in parietal regions (right superior parietal lobe and left precuneus) relative to pseudowords that required less structural analysis to arrive at an existing lexical representation. As the two sets were matched on cohort size and surface form, these results highlight the role of internal levels of morphological structure even in forms that do not possess a lexical representation.     

The neural correlates of retrieval and procedural strategies in mental arithmetic: A functional neuroimaging meta-analysis

Mental arithmetic is a complex skill of great importance for later academic and life success. Many neuroimaging studies and several meta-analyses have aimed to identify the neural correlates of mental arithmetic. Previous meta-analyses of arithmetic grouped all problem types into a single meta-analytic map, despite evidence suggesting that different types of arithmetic problems are solved using different strategies. We used activation likelihood estimation (ALE) to conduct quantitative meta-analyses of mental arithmetic neuroimaging (n = 31) studies, and subsequently grouped contrasts from the 31 studies into problems that are typically solved using retrieval strategies (retrieval problems) (n = 18) and problems that are typically solved using procedural strategies (procedural problems) (n = 19). Foci were compiled to generate probabilistic maps of activation for mental arithmetic (i.e., all problem types), retrieval problems, and procedural problems. Conjunction and contrast analyses were conducted to examine overlapping and distinct activation for retrieval and procedural problems. The conjunction analysis revealed overlapping activation for retrieval and procedural problems in the bilateral inferior parietal lobules, regions typically associated with magnitude processing. Contrast analyses revealed specific activation in the left angular gyrus for retrieval problems and specific activation in the inferior frontal gyrus and cingulate gyrus for procedural problems. These findings indicate that the neural bases of arithmetic systematically differs according to problem type, providing new insights into the dynamic and task-dependent neural underpinnings of the calculating brain.     

The neural substrate of human empathy: effects of perspective-taking and cognitive appraisal

Whether observation of distress in others leads to empathic concern and altruistic motivation, or to personal distress and egoistic motivation, seems to depend upon the capacity for self-other differentiation and cognitive appraisal. In this experiment, behavioral measures and event-related functional magnetic resonance imaging were used to investigate the effects of perspective-taking and cognitive appraisal while participants observed the facial expression of pain resulting from medical treatment. Video clips showing the faces of patients were presented either with the instruction to imagine the feelings of the patient ("imagine other") or to imagine oneself to be in the patient's situation ("imagine self"). Cognitive appraisal was manipulated by providing information that the medical treatment had or had not been successful. Behavioral measures demonstrated that perspective-taking and treatment effectiveness instructions affected participants' affective responses to the observed pain. Hemodynamic changes were detected in the insular cortices, anterior medial cingulate cortex (aMCC), amygdala, and in visual areas including the fusiform gyrus. Graded responses related to the perspective-taking instructions were observed in middle insula, aMCC, medial and lateral premotor areas, and selectively in left and right parietal cortices. Treatment effectiveness resulted in signal changes in the perigenual anterior cingulate cortex, in the ventromedial orbito-frontal cortex, in the right lateral middle frontal gyrus, and in the cerebellum. These findings support the view that humans' responses to the pain of others can be modulated by cognitive and motivational processes, which influence whether observing a conspecific in need of help will result in empathic concern, an important instigator for helping behavior.     

Putative neural substrate of normal and abnormal general movements

During the last decade it has become clear that the assessment of the quality of general movements (GMs) in foetus and young infant is a sensitive tool to evaluate the integrity of the young nervous system. GMs are movements in which all parts of the body participate. The hallmark of typical GMs is movement complexity and variation; in abnormal GMs movement complexity and variation is reduced or absent. Abnormal GMs may predict developmental outcome. Prediction on the basis of longitudinal series of GM assessments is best. Second best is prediction on the basis of an assessment at ‘fidgety’ GM age, i.e. at 2–4 months post-term. Definitely abnormal GMs at ‘fidgety’ age are related to cerebral palsy, mildly abnormal GMs to minor neurological dysfunction at school age. In the present paper the hypothesis is advanced that GM complexity and variation are brought about by the transiently present cortical subplate and that abnormal GMs are the result of damage or dysfunction of the subplate and its efferent motor connections in the periventricular white matter.