Functional Magnetic Resonance Imaging and Somatosensory Evoked Potentials in Rats With a Neonatally Induced Freeze Lesion of the Somatosensory Cortex

Abstract

Summary:Brain plasticity is an important mechanism for functional recovery from a cerebral lesion. The authors aimed to visualize plasticity in adult rats with a neonatal freeze lesion in the somatosensory cortex using functional magnetic resonance imaging (fMRI), and hypothesized activation outside the primary projection area. A freeze lesion was induced in the right somatosensory cortex of newborn Wistar rats (n ‫ס‬ 12). Sham-operated animals (n ‫ס‬ 7) served as controls. After 6 or 7 months, a neurologic examination was followed by recording of somatosensory evoked potentials (SSEPs) and magnetic resonance experiments (anatomical images, fMRI with blood oxygen level-dependent contrast and perfusion-weighted imaging) with electrical forepaw stimulation under ␣-chloralose anesthesia. Lesioned animals had no obvious neurologic deficits. Anatomical magnetic resonance images showed a malformed cortex or hyperintense areas (cysts) in the lesioned hemisphere. SSEPs were distorted and smaller in amplitude, and fMRI activation was significantly weaker in the lesioned hemisphere. Only in a few animals were cortical areas outside the primary sensory cortex activated. The results are discussed in respect to an apparent absence of plasticity, loss of excitable tissue, the excitability of the lesioned hemisphere, altered connectivity, and a disturbed coupling of increased neuronal activity to the hemodynamic response.

Feasibility of imaging evoked activity throughout the rat brain using electrical impedance tomography

“…Cortical evoked potentials recorded in this study had an average latency of 12.1 AE 1.6 ms which is consistent with Huttunen et al (2008), Koyanagi and Tator (1996) and Schwindt et al (2004) who report cortical evoked potentials occurring between 12 and 17 ms after forepaw stimulation under α-chloralose anaesthesia. There is greater variation in the magnitude of the evoked potential presented in literature which can be attributed to differing recording techniques.…”

Functional organization of human visual cortex in occipital polymicrogyria

“…Our results showed stimulus-driven fMRI modulation in the PMG. The finding that signals can be elicted from PMG is consistent with previous functional imaging studies of visual system in animals [Schwindt et al, 2004] and humans [Burneo et al, 2004;Innocenti et al, 2001;Janszky et al, 2003;Paetau et al, 2004].…”

“…Animal studies have demonstrated that PMG may show variable responses to stimulation in terms of activation and organization. Some studies have shown reduced activations with sensory stimulation [Schwindt et al, 2004], while other studies showed a disruption of cortical organization in the somatosensory cortex [Jacobs et al, 1999b;Rosen et al, 2001] and a disruption of retinotopic organization following lesions in the immature occipital cortex [Restrepo et al, 2003].…”

Use of magnetic stimulation to elicit motor evoked potentials, somatosensory evoked potentials, and H-reflexes in non-sedated rodents

“…Latencies of electrically induced SSEPs in rats reported by others (Nashmi et al, 1997;Schlag et al, 2001;Schwindt et al, 2004) are similar to those recorded in our study (Table 2). We compared electrically induced SSEPs in parallel with M-SSEPs which revealed slightly (but not significantly) shorter latencies but similar amplitudes.…”