Biomedical subjects

Li Min Chen

Publications and source records attributed to Li Min Chen.

4 recordsLinked to original sources

PubMed2005

Optical imaging of SI topography in anesthetized and awake squirrel monkeys.

Orderly topographic maps in the primary somatosensory cortex (SI) serve as an anchor for our understanding of somatosensory cortical organization. However, this view is mostly based on data collected in the anesthetized animal. Less is known about these topographies in the awake primate. Even less is known about the relative activations of different subdivisions of SI (areas 3a, 3b, 1, and 2). Toward the goal of understanding the functional activation of SI, we conducted intrinsic signal optical imaging of areas 3b and 1 in awake squirrel monkeys. Monkeys were imaged repeatedly for a period of >2 years in awake and anesthetized states in response to vibrotactile and electrocutaneous stimuli presented to individual fingerpads. During this period, we found stable somatotopic maps in both the anesthetized and awake states, consistent with electrophysiologically recorded maps in areas 3b and 1 in the anesthetized state. In the awake animal, signal sizes were larger, but variability was greater, leading to decreased signal-to-noise ratios. Topographic activations were larger (in both area and amplitude) in the awake animal, suggesting either a less precise topography and/or more complex integration. This brings into question the role of a precise topographic map during behavior. In addition, whereas in the anesthetized animal strongest imaging signals were obtained from area 3b, in the awake animal, area 1 activation dominated over that in area 3b. Differences in relative dominance of area 3b versus area 1 suggest that inter-areal interactions in the alert animal differ substantially from that in the anesthetized animal.

Anesthesia↗

PubMed2004

Modality maps within primate somatosensory cortex.

The sensations of pressure, flutter, and vibration are psychophysically distinct tactile modalities produced by frequency-specific vibrotactile stimulation of different mechanoreceptors in the skin. The information coded by the different low-threshold mechanoreceptors are carried by anatomically and electrophysiologically distinct pathways that remain separate at least up to and including the input stage of primary somatosensory cortex (SI) in primates, area 3b. Little is known about the functional organization of tactile representation beyond that stage. By using intrinsic optical imaging methods to record from area 1, the second processing stage of SI, we present evidence that pressure, flutter, and vibratory stimuli activate spatially distinct cortical domains in area 1, further strengthening the foundation for modality-specific processing streams in SI. These modality domains exhibit an organization that is unlike the discontinuous modality maps in visual area V2 but more like the continuous visual orientation maps in V1. The results demonstrate that psychophysically distinct sensory modalities can have fundamentally different modes of cortical representation.

Animals↗

PubMed2004

Intraoperative optical imaging of human face cortical topography: a case study.

We used intrinsic signal optical imaging to obtain maps of human somatosensory cortex during electrocutaneous stimulation of the face during a neurosurgical procedure for epilepsy. We found that human face somatotopy is organized like the macaque or cebus monkey, with peri-orbital skin located medial to peri-buccal skin, and that cortical magnification in the human is comparable to that in non-human primates. This study demonstrates that intrinsic signal imaging can be performed on humans during operative procedures with sufficient spatial resolution to reveal high-resolution topographic maps.

Adult↗

PubMed2002

A chamber and artificial dura method for long-term optical imaging in the monkey.

Optical imaging over extended periods of time in non-human primates presents serious challenges because the dura mater must be removed to expose the cortical surface. We present a novel nylon imaging chamber with a transparent artificial dura implant, which allows repeated, long-term optical recordings from the cortex. The cylinder of the chamber is inserted into a cranial trephination and held in place with a minimum of screws and acrylic cement. A round patch of artificial dura with a perpendicular wall protects the cortical surface and slows re-growth of dural tissue within the chamber. A cap, manufactured from the same material as the cylinder, is screwed into the chamber and seals it completely. Over a period of 1-4 months, the chamber required a minimum of maintenance and stayed infection-free without local antibiotic application. We repeatedly performed optical imaging in the same animal with the advantages of shortened preparation time. To permit precise alignment and comparison of maps obtained from different imaging sessions, we developed a program that calculated a 2-dimensional spatial transformation between maps of different magnifications, translations, and distortions. We suggest that these methods provide a practical solution to long-term optical imaging in the anesthetized or alert monkey. The exclusive use of non-metallic materials offers the benefit of a lighter and more compact implant, and the possibility to perform MRI scans after chamber implantation.

Anesthesia↗