Mapping The Cerebral Cortex
Andrew P. Wickens in A History of the Brain, 2014
By the mid-nineteenth century, few researchers interested in brain function would have accepted mental faculties could be localised to distinct regions of the cerebral cortex. Rather, he regarded the cerebral cortex as a single system whose diffused parts 'concur, consent and are in accord'. It was a pivotal moment when new theories of the cerebral cortex had to be formulated, not least when the Englishman John Hughlings Jackson provided clinical evidence to show the right and left cerebral hemispheres had different mental functions. His work was supported when a second language centre was discovered by Carl Wernicke in 1874. He was also an admirer of Gall's work, and by the early 1820s as a young doctor, had began to notice some individuals with speech loss had damage to the frontal part of their cerebral cortex. Language was not the only function to become associated with a specific area of the cerebral cortex.
Limits on Short-Term Plasticity in Somatosensory Cortex
Mark J Rowe, Yoshiaki Iwamura in Somatosensory Processing: From Single Neuron to Brain Imaging, 2001
Ultimately the limit on short-term unmasking-based plasticity resulting from discrete peripheral denervation must be set by the underlying anatomy. In addition to the role of local inhibition in limiting the extent of receptive fields which is implied from short-term unmasking studies, there are a number of direct physiological manifestations of the action of inhibitory intemeurons in the somatosensory cortex. In consideration of a possible source of tonic peripheral activity that may provide a source of input to central inhibitory neurons, C-fibre activity has been blocked using the selective neurotoxin, capsaicin. With extracellular recording from primary somatosensory cortex of anaesthetized macaque monkeys it was found that many neurons within the ‘hand’ representation had secondary receptive fields on the lower part of the face. The increased density, seen with anterograde transport of biocytin, was interpreted as resulting from axonal sprouting of intrinsic excitatory neurons and the formation of new terminal branches.
David Hunter Hubel (1926–2013) and Torsten Nils Wiesel (b. 1924)
Andrew P. Wickens in Key Thinkers in Neuroscience, 2018
David Hunter Hubel and Torsten Nils Wiesel will always be known for characterising the responses of single cells in the primary visual cortex, although they made many other groundbreaking discoveries concerning cortical architecture, along with highlighting the importance of experience in the visual system's development. Hubel and Wiesel identified the presence of "orientation columns". In brief, when they lowered a recording electrode perpendicularly into the visual cortex, they found that the receptive fields of the cells all had the same preferred line orientations. One of their most important was to show that the visual cortex consists of cube-like units, which they called 'hypercoloumns'. Hubel and Wiesel undertook an important work on the development of the visual cortex – and in particular the age at which the structure of the visual cortex was modifiable through experience. Another seminal contribution of Hubel and Wiesel was to demonstrate that the nature of visual processing is hierarchical.
Direct Comparison of Episodic Encoding and Retrieval of Words: An Event-related fMRI Study
Published in Memory, 1999
Kathleen B. McDermott, Jeffrey G. Ojemann, Steven E. Petersen, John M. Ollinger, Abraham Z. Snyder, Erbil Akbudak, Thomas E. Conturo, Marcus E. Raichle
Functional magnetic resonance imaging (fMRI) was used to compare directly episodic encoding and retrieval. During encoding, subjects studied visually presented words and reported via keypress whether each word represented a pleasant or unpleasant concept (intentional, deep encoding). During the retrieval phase, subjects indicated (via keypress) whether visually presented words had previously been studied. No reliable differences were found during the recognition phase for words that had been previously studied and those that had not been studied. Areas preferentially active during encoding (relative to retrieval) included left superior frontal cortex, medial frontal cortex, left superior temporal cortex, posterior cingulate, left parahippocampal gyrus, and left inferior frontal gyrus. Regions more active in retrieval than encoding included bilateral inferior parietal cortex, bilateral precuneus, right frontal polar cortex, right dorsolateral prefrontal cortex, and right inferior frontal/insular cortex.
Motor cortex stimulation in patients with post-stroke pain: Conscious somatosensory response and pain control
Published in Neurological Research, 2003
Chikashi Fukaya, Yoichi Katayama, Takamitsu Yamamoto, Kazutaka Kobayashi, Masahiko Kasai, Hideki Oshima
We analyzed the conscious sensory responses to cortical stimulation of 31 patients with post-stroke pain who underwent motor cortex stimulation (MCS) therapy. During surgery for electrode placement, a sensory response (tingle projected to a localized peripheral area) was elicited by high-frequency stimulation (50 Hz) in 23 (84%) from the somatosensory cortex, and in 16 (52%) from the motor cortex without muscle contraction. Unpleasant painful sensation was induced or their original pain was exacerbated in 12 patients (39%) when the somatosensory cortex was stimulated and in two (6%) when the motor cortex was stimulated. Somatosensory responses were induced in eight (25%) even by low-frequency stimulation (1–f the motor cortex at an intensity below the threshold for muscle contraction. In contrast, among 20 nonpain patients who underwent a similar procedure for cortical mapping in epilepsy or brain tumor surgery, a sensory response was produced by high-frequency stimulation in only eight (40%; p < 0.02) from the somatosensory cortex and four (20%; p < 0.03) from the motor cortex. Pain sensation was not induced by stimulation of the somatosensory cortex (p < 0.002) or motor cortex in any of these patients. In addition, none of these patients reported a sensory response to low-frequency stimulation. In both of the two post-troke pain patients who reported abnormal pain sensation in response to stimulation of the motor cortex, MCS failed to control their post-stroke pain. These findings imply that the sensitivity of the perceptual system even to activity of the motor cortex is heightened in post-stroke pain patients, which can sometimes hinder pain control by MCS.
The organization of somatosensory cortex in the short-tailed opossum ( Monodelphis domestica )
Published in Somatosensory & Motor Research, 2000
K. C. Catania, N. Jain, J. G. Franca, E. Volchan, J. H. Kaas
The organization of neocortex in the short-tailed opossum ( Monodelphis domestica ) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.