Biomedical subjects

Alexander Leff

Publications and source records attributed to Alexander Leff.

3 recordsLinked to original sources

PubMed2004

A historical review of the representation of the visual field in primary visual cortex with special reference to the neural mechanisms underlying macular sparing.

This article comprises a historical review of the literature pertaining to the representation of the visual field in human primary visual cortex. A brief survey of the anatomy of the visual system is followed by a critical evaluation of the key studies that have informed both the issue of the disproportionate representation of central vision within primary visual cortex, and the anatomical basis underlying the phenomena of macular sparing and macular splitting hemianopia.

Hemianopsia↗

PubMed2003

Defining a left-lateralized response specific to intelligible speech using fMRI.

Functional imaging studies of language have shown bilateral superior temporal activations in response to 'passive' perception of speech when the baseline condition did not control for the acoustic complexity of speech. Controlling for this complexity demonstrates speech-specific processing lateralized to the left temporal lobe, and our recent positron emission tomography study has emphasized a role for left anterolateral temporal cortex in speech comprehension. This contrasts with the more usual view that relates speech comprehension to left temporal-parietal cortex, the ill-defined area of Wernicke. This study attempted to reconcile these differences, using a more sensitive 3 T functional magnetic resonance imaging system, and a sparse sampling paradigm. We found left lateralized activations for intelligible speech with two distinct foci, one in the anterior superior temporal sulcus and the other on the posterior temporal lobe. Therefore, the results demonstrate that there are neural responses to intelligible speech along the length of the left lateral temporal neocortex, although the precise processing roles of the anterior and posterior regions cannot be determined from this study.

Acoustic Stimulation↗

PubMed2002

A physiological change in the homotopic cortex following left posterior temporal lobe infarction.

We investigated the relationship between cerebral activity (measured with positron emission tomography) and word rate in normal subjects and aphasic patients listening to monosyllabic words at rates up to those encountered in normal speech. By measuring the slope of the regression of the individual activity-word rate responses in the temporal cortex in normal subjects, we identified a functional asymmetry in the posterior superior temporal sulcus. The response was greater (steeper) on the left. Using the same study design, we identified a steeper activity-word rate response in the right posterior superior temporal sulcus of patients who had recovered single-word auditory comprehension after infarction of the left posterior temporal cortex. This response was significantly different from that observed in both normal subjects and a group of patients with left hemisphere infarcts that spared the posterior temporal cortex. The results demonstrated a change in physiological responsiveness in the contralateral homotopic cortex after posterior temporal infarction.

Adult↗