Differences In Cortical Organization Research Articles

Functional System and Areal Organization of a Highly Sampled Individual Human Brain

Resting state functional MRI (fMRI) has enabled description of group-level functional brain organization at multiple spatial scales. However, cross-subject averaging may obscure patterns of brain organization specific to each individual. Here, we characterized the brain organization of a single individual repeatedly measured over more than a year. We report a reproducible and internally valid subject-specific areal-level parcellation that corresponds with subject-specific task activations. Highly convergent correlation network estimates can be derived from this parcellation if sufficient data are collected-considerably more than typically acquired. Notably, within-subject correlation variability across sessions exhibited a heterogeneous distribution across the cortex concentrated in visual and somato-motor regions, distinct from the pattern of intersubject variability. Further, although the individual's systems-level organization is broadly similar to the group, it demonstrates distinct topological features. These results provide a foundation for studies of individual differences in cortical organization and function, especially for special or rare individuals. VIDEO ABSTRACT.

Role of cortical reorganization on the effect of 5-HT pharmacotherapy for spinal cord injury

Cortical reorganization or expansion of the intact cortical regions into the deafferented cortex after complete spinal transection in neonatally spinalized rats was shown to be essential for increases in weight-supported stepping at adulthood. The novel somatotopic organization identified in these animals can be induced by exercise or spinal transplants that bridge the site of injury. However, the role of cortical reorganization in increased weight-supported (WS) stepping after pharmacotherapy is unknown. For the neonatally spinalized rat model, the 5-HT2C receptor agonist 1-(m-chlorophenyl)-piperazine hydrochloride (mCPP) increases the number of WS steps taken when administered to adult rats spinalized as neonates (mCPP+) though not all animals showed this effect (mCPP−). Since no differences in the behavior of the animals off-drug has been demonstrated, it is unclear why acute administration of 5-HT affects only a subset of animals. One possibility is that differences in cortical organization between mCPP+ and mCPP− may contribute to the differences in the functional effect of mCPP. To test this, we recorded from single neurons in the deafferented hindlimb sensorimotor cortex during passive sensory stimulation of the cutaneous surface of the forepaws and during active sensorimotor stimulation of the forepaws while the animals locomoted on a motorized treadmill. Our results show that neurons recorded from mCPP+ animals increased their responsiveness to both passive and active stimulation off-drug in comparison to neurons from mCPP− animals. These data suggest that differences in the cortical organization of mCPP+ compared to mCPP− animals may be at least partially responsible for the effect of a 5-HT2C receptor agonist on functional outcome.

Language networks in anophthalmia: maintained hierarchy of processing in ‘visual’ cortex

Imaging studies in blind subjects have consistently shown that sensory and cognitive tasks evoke activity in the occipital cortex, which is normally visual. The precise areas involved and degree of activation are dependent upon the cause and age of onset of blindness. Here, we investigated the cortical language network at rest and during an auditory covert naming task in five bilaterally anophthalmic subjects, who have never received visual input. When listening to auditory definitions and covertly retrieving words, these subjects activated lateral occipital cortex bilaterally in addition to the language areas activated in sighted controls. This activity was significantly greater than that present in a control condition of listening to reversed speech. The lateral occipital cortex was also recruited into a left-lateralized resting-state network that usually comprises anterior and posterior language areas. Levels of activation to the auditory naming and reversed speech conditions did not differ in the calcarine (striate) cortex. This primary 'visual' cortex was not recruited to the left-lateralized resting-state network and showed high interhemispheric correlation of activity at rest, as is typically seen in unimodal cortical areas. In contrast, the interhemispheric correlation of resting activity in extrastriate areas was reduced in anophthalmia to the level of cortical areas that are heteromodal, such as the inferior frontal gyrus. Previous imaging studies in the congenitally blind show that primary visual cortex is activated in higher-order tasks, such as language and memory to a greater extent than during more basic sensory processing, resulting in a reversal of the normal hierarchy of functional organization across 'visual' areas. Our data do not support such a pattern of organization in anophthalmia. Instead, the patterns of activity during task and the functional connectivity at rest are consistent with the known hierarchy of processing in these areas normally seen for vision. The differences in cortical organization between bilateral anophthalmia and other forms of congenital blindness are considered to be due to the total absence of stimulation in 'visual' cortex by light or retinal activity in the former condition, and suggests development of subcortical auditory input to the geniculo-striate pathway.

Visual orienting and alerting in rhesus monkeys: comparison with humans

The behavioral capacities of the rhesus monkey for several sensory and cognitive tasks appear quite similar to those of humans. To evaluate the monkey's attentional capacities, we have compared monkey and human performance on a visuospatial attentional task, the cued target detection [dyCTD) paradigm. Animals were trained to fixate a small spot of light while a cue and a subsequent target, are flashed in the visual periphery. In valid trials, the cue and target appeared in the same spatial location; in invalid trials, the cue and target appeared in the opposite location; in double trials, two cues were presented and the target appeared in one of their locations; in no-cue trials, the cue was omitted and the target appeared in one location. In addition, we varied cognitive control over the task initiation by making the trial onset either self-paced or computer-paced. Reaction times (RTs) to target presentation, response accuracy, and frequency of aborted trials were measured for all subjects. No significant species differences were found for the patterns of RTs for different trial types or for attentional dynamics, as indexed by the decreases in RT with increasing cue-target interval. However, humans and non-human primates reacted differently to changes in cognitive control. Humans shows significant increases in no-cue trial RTs in the auto-paced task compared to the self-paced, but no differences in overall RT between tasks; monkeys showed a significant faster overall RT for the self-paced than the computer-paced task, but no difference between no-cue RTs. The performance differences between species may be related to the training history of the animals or to known anatomical differences in cortical organization, especially in the parietal lobe.

Cortical organization after treatment of a peripheral nerve with ricin: an evaluation of the relationship between sensory neuron death and cortical adjustments after nerve injury.

The present study was designed to assess whether cortical changes after peripheral nerve damage are related to the degree of death of primary sensory neurons in the damaged nerve. The cytotoxin ricin was injected into the sciatic nerves of adult rats to kill primary sensory neurons with axons through the injection site. Following periods of 6-101 days, the S-I hindpaw map was evaluated with neurophysiological techniques and compared with the hindpaw maps of previously studied normal adult rats and adult rats that had undergone adult or neonatal sciatic section at a comparable level of the nerve. These comparisons allowed evaluation of cortical functional organization following different degrees of sensory neuron loss after sciatic nerve injury. There were three main results. 1) The comparison of ricin-treated and normal adult rats indicated that ricin treatment interrupted inputs from the sciatic skin territory on the hindpaw and caused a limited increase in the size of the cortical area that was activated by stimulation of hindpaw skin innervated by the remaining saphenous nerve. 2) The cortical maps of rats that had undergone adult ricin treatment (relatively large primary neuron loss) or section during adulthood (small to moderate primary neuron loss) were similar. In both groups, only the saphenous hindpaw skin was represented in cortex, and the cortical area that was activated by stimulation of the saphenous hindpaw skin had undergone a comparable limited enlargement. 3) The comparison of ricin-treated adult rats (relatively large primary neuron loss) and adult rats that had undergone neonatal section (relatively large primary neuron loss) indicated that cortical organization differed after these treatments. In particular, after ricin treatment the cortical area that was activated by stimulation of the saphenous hindpaw skin was larger than the comparable area in neonatal denervates, and the topographical progressions between the hindpaw and adjacent body representations were not as variable as after neonatal section. These findings indicate that cortical maps are altered after injection of ricin into a nerve. The similarity in cortical organization after ricin treatment (relatively large sensory neuron loss) and nerve section in adults (relatively small sensory neuron loss) and the differences in cortical organization after ricin treatment and nerve section in neonates (both relatively large sensory neuron loss) indicate cortical changes do not covary as a simple function of the degree of peripheral neuron death.