Mapping cortical representations of the rodent forepaw and hindpaw with BOLD fMRI reveals two spatial boundaries

Abstract

Electrical stimulation of the rat forepaw and hindpaw was employed to study the spatial distribution of BOLD fMRI. Averaging of multiple fMRI sessions significantly improved the spatial stability of the BOLD signal and enabled quantitative determination of the boundaries of the BOLD fMRI maps. The averaged BOLD fMRI signal was distributed unevenly over the extent of the map and the data at the boundaries could be modeled with major and minor spatial components. Comparison of three-dimensional echo-planar imaging (EPI) fMRI at isotropic 300 μm resolution demonstrated that the border locations of the major spatial component of BOLD signal did not overlap between the forepaw and hindpaw maps. Interestingly, the border positions of the minor BOLD fMRI spatial components extended significantly into neighboring representations. Similar results were found for cerebral blood volume (CBV) weighted fMRI obtained using iron oxide particles, suggesting that the minor spatial components may not be due to vascular mislocalization typically associated with BOLD fMRI. Comparison of the BOLD fMRI maps of the forepaw and hindpaw to histological determination of these representations using cytochrome oxidase (CO) staining demonstrated that the major spatial component of the BOLD fMRI activation maps accurately localizes the borders. Finally, 2–3 weeks following peripheral nerve denervation, cortical reorganization/plasticity at the boundaries of somatosensory limb representations in adult rat brain was studied. Denervation of the hindpaw caused a growth in the major component of forepaw representation into the adjacent border of hindpaw representation, such that fitting to two components no longer led to a better fit as compared to using one major component. The border of the representation after plasticity was the same as the border of its minor component in the absence of any plasticity. It is possible that the minor components represent either vascular effects that extend from the real neuronal representations or the neuronal communication between neighboring regions. Either way the results will be useful for studying mechanisms of plasticity that cause alterations in the boundaries of neuronal representations.

Functional magnetic resonance microscopy at single-cell resolution in Aplysia californica

“…The difference between the two stimulation times was 5%, on average, over all 14 identified cells. These results are in agreement with previous reports showing that exposure to food stimuli soon elicits a state of food-induced arousal and food consumption, which can last tenths of minutes and is associated with an increase in the neuronal excitability in several ganglia, including the buccal ganglia (7,22). However, prolonged stimulation leads to a gradual decrease in these behavioral and neuronal responses as a result of satiation, sensory adaptation, and habituation (23-25).…”

“…These data agreed well with the strong increase in the Mn 2+ concentration measured in the buccal ganglia coming from animals that were allowed to ingest food (STIM1 or STIM3). Moreover, the presence of food in the animal's surrounding environment, in contrast to its presence in the buccal cavity, stimulates the perioral zone (lips and rhinophores) and generates an appetitive behavior that does not require neuronal activity in the buccal ganglia (7,23). The stimuli from this perioral zone are conveyed by peripheral nerves to the cerebral ganglion, which triggers activity in neuronal networks that are primarily located in the pedal-pleural ganglia rather than the buccal ganglia.…”

“…Among these techniques, MRI has been extensively applied to functional studies of mammalian brains. At present, the highest spatial resolution of such MRI experiments is of the order of (0.3 mm) 3 , averaging the signal from clusters of hundreds of neurons (7). Magnetic resonance (MR) microscopy (MRM) achieves higher resolution (of only a few micrometers) but requires long acquisition times, which prohibit its application to studying individual neurons in mammalian brains (8,9).…”

Imaging the Spatio-Temporal Dynamics of Supragranular Activity in the Rat Somatosensory Cortex in Response to Stimulation of the Paws

“…Electrophysiological studies of the infragranular layers have similarly shown larger responses to forepaw stimulation compared with hindpaw stimulation both with single-neuron recordings [48] and with local field potentials [51]. Moreover, studies employing intrinsic optical imaging [52] and BOLD fMRI [53] have also shown the same result. Larger responses to forepaw compared to hindpaw stimuli could therefore represent a general property of the rat somatosensory system.…”

The Characteristics of Brain Structural Network in Patients with Low Grade Glioma Revealed by Diffusion Tensor Imaging

“…In recent years, blood oxygenation level dependence functional MRI (BOLD-fMRI) has demonstrated its particular value in preoperative risk assessment in patients with LGG, which can facilitate planning of surgery, shorten the duration of the operation, and obtain prognostic information prior to surgery [3]. Nevertheless, BOLD-fMRI only provides information on cortical representation of brain function, but not on the course of the subcortical and deep white matter tracts [4,5]. As the white matter possesses about 50% of the adult brain volume and consists of a complex array of neuronal fiber connectivity [6], brain lesions often affect the white matter and may alter the known anatomical path in which the fiber pass.…”