Stimulation of STN impairs aspects of cognitive control in PD.

OBJECTIVE: To test the hypothesis that subthalamic nucleus (STN) stimulation in Parkinson disease (PD) patients affects working memory and response inhibition performance, particularly under conditions of high demand on cognitive control. METHODS: To test this hypothesis, spatial working memory (spatial delayed response [SDR]) and response inhibition (Go-No-Go [GNG]) tasks requiring varying levels of cognitive control were administered to patients with PD with previously implanted bilateral STN stimulators (n = 24). Patients did not take PD medications overnight. Data were collected while bilateral stimulators were on and off, counterbalancing the order across subjects. RESULTS: On the SDR task, STN stimulation decreased patients' working memory performance under a high but not low memory load condition (effect of stimulator condition on high load only and condition x load interaction, p < 0.05). On the GNG task, STN stimulation reduced discriminability on a high but not medium inhibition condition (effect of stimulator condition on high inhibition level only, p = 0.05; condition x inhibition level interaction, p = 0.07). CONCLUSION: STN stimulation reduces working memory and response inhibition performance under conditions of greater challenge to cognitive control despite significant improvement of motor function.

Cortical and subcortical blood flow effects of subthalamic nucleus stimulation in PD.

OBJECTIVE: To assess whether subthalamic nuclei (STN) stimulation's primary mechanism of action is to drive or inhibit output neurons. METHODS: Cerebral blood flow responses to STN stimulation were measured using PET in 13 patients with Parkinson disease. Patients were scanned with stimulators off and on (six scans each condition). Clinical ratings, EMG, and videotaping of movements were obtained at each scan. Scans with observable tremor or movement were eliminated from analysis. Brain regions where STN stimulation significantly altered blood flow were identified. RESULTS: STN stimulation increased blood flow in midbrain (including STN), globus pallidus, and thalamus, primarily on the left side, but reduced blood flow bilaterally in frontal, parietal, and temporal cortex. CONCLUSIONS: These data suggest that STN stimulation increases firing of STN output neurons, which increases inhibition of thalamocortical projections, ultimately decreasing blood flow in cortical targets. STN stimulation appears to drive, rather than inhibit, STN output neurons.

Wada testing reveals frontal lateralization for the memorization of words and faces.

Neuroimaging studies have suggested that specific regions of the frontal and medial temporal cortex are engaged during memory formation. Further, there is specialization across these regions such that verbal materials appear to preferentially engage the left regions while nonverbal materials primarily engage the right regions. An open question, however, has been to what extent frontal regions contribute to successful memory formation. The present study investigates this question using a reversible lesion technique known as the Wada test. Patients memorized words and unfamiliar faces while portions of their left and right hemispheres were temporarily anesthetized with sodium amytal. Subsequent memory tests revealed that faces were remembered better than words following left-hemisphere anesthesia, whereas words were remembered better than faces following right-hemisphere anesthesia. Importantly, inspection of the circulation affected by the amytal further suggests that these memory impairments did not result from direct anesthetization of the medial temporal regions. Taken in the context of the imaging findings, these results suggest that frontal regions may also contribute to memory formation in normal performance.

Rapid optical imaging of whisker responses in the rat barrel cortex.

Videomicroscopy was used to image 'intrinsic' responses over the rat barrel cortex through a closed cranial window during controlled whisker stimulation. With a Macintosh IIfx running Image 1.49 VDM, video frames from a CCD camera were captured and averaged before, during and after whisker stimulation. The technique presented here is a functional imaging modality--using conventional videomicroscopic equipment, a small computer, and public domain NIH Image software--with a temporal resolution of 33 ms. Images can be obtained directly from the CCD camera or recorded to videotape for post hoc analysis. Pixel by pixel comparison of prestimulation images to images obtained during stimulation revealed changes in the reflectance characteristics of cortex and vessels overlying the barrel field. Imaged responses superimposed on barrel histology to map intrinsic signal matched barrels of the stimulated whiskers in every case. Video imaging of the rat barrel cortex provides a useful method for rapid targeting for other experimental protocols and has potential for analyzing localized responses to physiologic stimuli in vivo.

LCBF changes in rat somatosensory cortex during whisker stimulation monitored by dynamic H2 clearance.

We evaluated increases in local cerebral blood flow (LCBF) localized to single activated cortical columns by H2 clearance methods. The rat whisker-barrel cortex is a model for cortical function and neural processing in active explorative behaviors. Up to four 30-40 microns Pt wire electrodes were inserted in or near the rat whisker-barrel cortex. Electrode positions were mapped by postmortem histology. H2 was generated electrochemically by constant current from one electrode and detected by one or more other electrodes 300-500 microns away. Changes in LCBF produced inverse changes in PH2. Shifts during steady H2 generation were calibrated against standard H2 inhalation clearance curves at rest and during inhalation of 7.5% CO2 for 1 min for quantitative estimates of LCBF. Contralateral whisker stimulation at 3 Hz, 1 min duration and delivered every 2 min produced the largest increases in LCBF. LCBF responses were detected in approximately 1 s. Stimulation of single whiskers produced the largest responses when an electrode was in the corresponding barrel. These results indicate that increased neural activity in a single cortical column produces blood flow responses primarily in that column.

"Nulla per os [NPO] after midnight" reassessed.

The concept that fasting produces an "empty stomach" has been shown to be incorrect. Numerous studies demonstrate that fasting neither diminishes gastric volume nor decreases gastric acidity and the risk of pulmonary aspiration is not increased by the preoperative intake of clear liquids. Nevertheless, most surgeons and anesthesiologists continue to adhere to the traditional NPO after midnight tradition, a tradition which should be abandoned. Withholding fluids preoperatively is not only of no benefit to patients but may even be harmful. Based on current knowledge and experience, the following guidelines, which represent a beneficial and humane advance for all surgical patients, are recommended. 1) Adults and children undergoing elective surgery under general anesthesia as inpatients or outpatients in good health (ASA Class I or II) and without specific contra-indications (such as morbid obesity, gastrointestinal disease, etc.) should be allowed and encouraged to drink clear fluids up to two hours before surgery. 2) Patients undergoing elective surgery under general anesthesia and major regional blocks that might require conversion to general anesthesia should remain NPO for solids and non-clear liquids for a minimum of six hours before scheduled surgery. 3) Patients undergoing elective surgery under regional local anesthesia in good health and without specific contra-indication should be allowed and encouraged to have their normal breakfast and fluids as desired on the day of surgery.

Primary glaucoma associated with iridotrabecular dysgenesis and ectropion uveae.

We present nine patients with unilateral congenital ectropion uveae (hyperplasia of the iris pigment border), iris hypoplasia, characteristic gonioscopic findings, and glaucoma. A majority of these patients also demonstrated mild ptosis. In none of these patients were there any associated systemic abnormalities. The apparent ectropion uveae results from spread of the iris pigment epithelium beyond the iris ruff and onto the anterior surface of the iris. In two patients with this abnormality, histopathologic and electron microscopic findings are presented. All patients with congenital ectropion uveae should be carefully examined periodically to detect glaucoma.

A survey of current cataract surgical techniques.

A survey of 674 ophthalmologists in the United States confirmed that intraocular implants, along with extracapsular extraction and ambulatory surgery, are emerging as widely practiced surgical techniques. The data were analyzed geographically and statistically significant differences by region were found. More ophthalmic surgeons are likely to use both extracapsular extractions and ambulatory surgery in the future.