Role of Lead in the Central Nervous System: Effect on Electroencephlography, Evoked Potentials, Electroretinography, and Nerve Conduction.

The toxic effects of lead on the brain are well known, but its effects on EEG and evoked potentials (EPs) are not generally known in the neurodiagnostic community. Despite public health efforts, lead is still widely present at low levels in the environment. Even at low concentrations, lead is known to cause biochemical and physiological dysfunction. The present article reviews the effects of lead exposure on the central nervous system, with a special emphasis on the developing brain. Additionally, it describes the effects of lead on EEG, EPs, electroretinography, and nerve conduction studies.

Single-unit responses selective for whole faces in the human amygdala.

The human amygdala is critical for social cognition from faces, as borne out by impairments in recognizing facial emotion following amygdala lesions [1] and differential activation of the amygdala by faces [2-5]. Single-unit recordings in the primate amygdala have documented responses selective for faces, their identity, or emotional expression [6, 7], yet how the amygdala represents face information remains unknown. Does it encode specific features of faces that are particularly critical for recognizing emotions (such as the eyes), or does it encode the whole face, a level of representation that might be the proximal substrate for subsequent social cognition? We investigated this question by recording from over 200 single neurons in the amygdalae of seven neurosurgical patients with implanted depth electrodes [8]. We found that approximately half of all neurons responded to faces or parts of faces. Approximately 20% of all neurons responded selectively only to the whole face. Although responding most to whole faces, these neurons paradoxically responded more when only a small part of the face was shown compared to when almost the entire face was shown. We suggest that the human amygdala plays a predominant role in representing global information about faces, possibly achieved through inhibition between individual facial features.

Statistical parameters of epileptiform brain activity differentiate frontal and temporal lobe patients.

Statistical properties of electromagnetic brain activity may increase the understanding of the human brain by providing precise numerical vales associated with neuronal activity. A statistical analysis was performed on frontal and temporal lobe patients to investigate possible differences between the two populations. Results were then compared to clinical results to confirm findings. Frontal lobe patients had a larger spatial distribution of interictal spikes when compared to temporal lobe patients. Statistical properties from interictal spike data may differentiate patients with frontal and temporal lobe epilepsy.

Hemispheric language dominance in magnetoencephalography: sensitivity, specificity, and data reduction techniques.

Understanding the areas involved in language functions not only enables investigators to understand neuroanatomical structures, but may be a promising technique in the presurgical evaluation of epilepsy. The predictive power of various data reduction techniques was tested on language data obtained by magnetoencephalography (MEG) of 16 patients and 12 control subjects. Words were presented aurally in two phases: the study phase and the recognition phase. Subjects were asked to remember words from the study phase and indicate if they remembered those words during the recognition phase. Single equivalent-current dipoles were calculated to determine laterality indices and the neuroanatomical correlates of language function. For all patients, results indicated a concordance, sensitivity, and specificity of 0.75. After consideration of IQ scores and exclusion from the analysis of those patients with scores below the average range, the results indicated a concordance of 0.90, sensitivity of 0.86, and specificity of 1.00. These findings are consistent with previous MEG investigations of language function in comparison with the Wada technique and support the use of MEG language mapping in most patients with an IQ within or above the average range.

Spatial selectivity in human ventrolateral prefrontal cortex.

The functional organization of lateral prefrontal cortex is not well understood, and there is debate as to whether the dorsal and ventral aspects mediate distinct spatial and non-spatial functions, respectively. We show for the first time that recordings from human ventrolateral prefrontal cortex show spatial selectivity, supporting the idea that ventrolateral prefrontal cortex is involved in spatial processing. Our results also indicate that prefrontal cortex may be a source of control signals for neuroprosthetic applications.