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Biomedical subjects

I Derakhshan

Publications and source records attributed to I Derakhshan.

At least 19 recordsLinked to original sources
PubMed2006

Crossed-uncrossed difference (CUD) in a new light: anatomy of the negative CUD in Poffenberger's paradigm.

Crossed Uncrossed Differentials (CUDs) have long been used as surrogate for the interhemispheric transfer time (IHTT). Evidence is presented that macular vision is the province of the major hemisphere, wherein all commands are initiated regardless of the laterality of the effectors of such commands. Using clinical and time-resolved data it is shown also that the above arrangement (i.e. neural handedness) corresponds to the subject's behavioral avowed (avowed, self-declared) handedness only in a statistical sense; with a substantial minority of humanity displaying a disparity of neural and behavioral handedness. Evidence is provided that the negative CUD in previously reported studies was a reflection of such incongruity in those subjects studied. Thus, to lateralize the command center it is sufficient to determine the reaction time of two symmetrically located effectors on the body. The side with longer reaction time is ipsilateral to the major hemisphere, with the difference of the two sides commensurate to transcallosal IHTT.

Brain↗
PubMed2006

Laterality of seizure onset and the simple reaction time: revamping the Poffenberger's paradigm for seizure surgery.

BACKGROUND: Crossed-uncrossed differentials (CUDs) are viewed as surrogates for interhemispheric transfer time (IHTT). Not uncommonly CUDs assume statistically significant negative values (inverted CUDs). This raises doubts of the accepted interpretation of CUDs, i.e. intra- and inter-hemispheric routings of signals in uncrossed and crossed responses, respectively. METHOD: Based on the evidence supporting directionality in callosal traffic, data are provided indicating that callosal transfers exclusively involve non-dominant responses and such transfers are modality non-specific. The evidence also indicates that neural handedness corresponds to behavioral only in a statistical manner and the former remains unchanged regardless of the subject's life experience. RESULTS: The neurally dominant side is the side that is directly connected to the major hemisphere (command center). The connection of the non-dominant side to the command center is via the corpus callosum; therefore, a delay occurs in the reaction time of all non-dominant effectors, corresponding to IHTT. Accordingly, negative CUDs indicate a mismatch of neural and behavioral (avowed) handedness of the subject. This group comprises a minority of 15-20% of the population. CONCLUSION: Comparing the response time of symmetrically located effector is a robust way of lateralizing a person's major hemisphere. The latter is also the site of initiation of seizures, as the minor hemisphere is bereft of independent motor activity. Sensory signals arising from the nondominant side of the body traverse the callosum before reaching the major hemisphere. Searching for ipsilateral somatosensory evoked potentials provides another approach in lateralizing the non-dominant side of the body (ipsilateral to the major hemisphere). Practical uses of a conceptually revamped Poffenberger paradigm in neurosurgery are briefly reviewed.

Cerebral Cortex↗
PubMed2005

Anatomy of handedness and the laterality of seizure onset: surgical implications of new understandings in motor control.

OBJECTIVES: This article pursues another corollary of the anatomy of handedness, a code for the laterality of motor control. The latter indicates the absence of any motor communication from the minor (right, in the vast majority of population) to the major hemisphere (left, in the vast majority of right handers). It also indicates that all communications between the two hemispheres are excitatory in nature. This arrangement prohibits initiation of seizure within the minor and its propagation to the major hemisphere, via the callosum. METHODS: A comprehensive review of the literature is undertaken regarding theoretical and technical reasons for the failure of seizure surgery in subjects undergoing the same for intractable epilepsy. RESULTS: Whereas the laterality of motor control is heavily biased towards the left hemisphere (approximately 80%), the operation is performed equally on both hemispheres. Failures of surgery in some series were substantially higher among those who had undergone operations on the right hemisphere. Technical reasons for this are traced to the unreliability of tests commonly employed in securing laterality of seizure onset, which is the same as that of motor control. Accordingly, the failure rate of seizure surgery may equal the rate of false lateralization of the major hemisphere in these circumstances. CONCLUSION: Given the dichotomous anatomy of handedness, the most robust test for lateralizing the hemisphere of onset of seizure is that of determining the reaction times of two symmetrically located effectors, one on each side of the body. The side with the shorter reaction time will always be opposite to the major hemisphere. The difference between the two values is commensurate to the inter-hemispheric transfer time.

Brain↗
PubMed2004

Handedness and macular vision: laterality of motor control underpins both.

This article pursues the corollaries of the anatomy of handedness recently discovered. Specifically, it addresses the issues concerning central vision as it relates to the command center and the circuitry of the saccades. It presents data that support the directionality of callosal traffic in motor and sensory realms even further. Evidence is presented that denotes a relationship between the anatomy sustaining movement control and that responsible for the part of the vision handled by the maculae. The evidence shows bypassing of the callosum by fibers serving the central vision. This aspect has ramifications for surgical approach to the third ventricle by callosotomy, relaxing the earlier prohibitions advocated in approaching the third ventricle via splenectomy.

Brain Mapping↗
PubMed2003

Callosum and movement control: case reports.

This article explores the role of directionality of callosal traffic (codified as handedness), based on personal clinical observations and a critical review of the literature. Based on this evidence, a technical definition of handedness is offered as opposed to the behavioral method in use until now. In the vast majority of right-handers neural and behavioral handedness match. The situation is the opposite in left-handers where two thirds of them are wired to be right-handers, causing the well-known heterogeneity seen in left-handed cohorts. The callosum-length proximity of the dominant side of the body to the command center in the major hemisphere is the source of its neurophysiological superiority compared to the nondominant side. Clinical syndromes in which the new scheme are manifested are reviewed, indicating the existence of an excitatory influence by the neuronal aggregate devoted to voluntary actions, housed in the major hemisphere, on their counterparts in the minor hemisphere. The latter is exclusively devoted to volitional movements occurring on the nondominant side. Thus, it is the directionality of callosal traffic that is responsible for cerebral asymmetries seen in the motor realm.

Adult↗