Biomedical subjects

Giri P Krishnan

Publications and source records attributed to Giri P Krishnan.

5 recordsLinked to original sources

PubMed2006

Psychophysiological evidence of altered neural synchronization in cannabis use: relationship to schizotypy.

OBJECTIVE: Cannabis use may produce neurophysiological disturbances similar to those observed in schizophrenia, particularly in relation to altered neural synchronization. Therefore, the current experiment examined the effect of cannabis use on EEG neural synchronization using the auditory steady-state evoked potential. METHOD: Auditory steady-state evoked potentials were assessed using varying rates of stimulation (auditory click-trains of 20, 30, 40 Hz) in current cannabis users (N=17) and drug-naive comparison subjects (N=16). EEG spectral power and signal-to-noise ratio at each stimulation frequency were compared between groups. RESULTS: Cannabis users showed decreased EEG power and signal-to-noise ratio at the stimulation frequency of 20 Hz. In addition, current cannabis users demonstrated increased schizotypal personality characteristics as assessed with the Schizotypal Personality Questionnaire, which positively correlated with total years of cannabis use. Finally, within the cannabis group, 20-Hz power values were negatively correlated with Schizotypal Personality Questionnaire scores. CONCLUSIONS: These data provide evidence for neural synchronization and early-stage sensory processing deficits in cannabis use. This finding, along with the observed increased rates of schizotypy in cannabis users, adds support for a cannabinoid link to schizophrenia spectrum disorders.

Acoustic Stimulation↗

PubMed2005

The effect of cannabis use and gender on the visual steady state evoked potential.

OBJECTIVE: Cannabis use often induces subjective distortions of perception. However, little work has been done examining the electroencephalographic (EEG) correlates of early sensory processing in cannabis users. The present study therefore examined visual function in cannabis users as assessed via the steady state visual evoked potential. (SSVEP). METHODS: SSVEPs were examined in current cannabis users (n = 17; 59% male; mean age = 23.2 (S.D. = 5.3)) and drug-naive controls (n = 16; 38% male; mean age = 21.3 (S.D. = 3.1)) to periodic photic stimulation presented at 18 and 25 Hz. The visual SSVEP was quantified via spectral power and the phase-locking factor (PLF) at each frequency of stimulation. The transient N160 event-related potential (ERP) was also evaluated at stimulus onset. RESULTS: The results showed that for both frequencies, female subjects in general displayed larger visual SSVEPs. A significant gender X group interaction also occurred at 18 Hz of stimulation, and age of onset of cannabis use positively correlated with 18 Hz spectral power values. Finally, the transient N160 component was shown to be reduced in cannabis users, regardless of gender. CONCLUSIONS: The present study was the first to demonstrate altered visual SSVEPs in cannabis users, and extends previous research demonstrating increased steady state responses in female subjects. While decreased SSVEPs provide initial evidence of altered oscillatory properties in primary visual circuits, reduction of the transient N160 component suggests disruption of later-stage visual processing in cannabis users. SIGNIFICANCE: These data provide evidence of cannabinoid modulation of sensory/perceptual function in the visual system, and indicates that cannabis use may affect the oscillatory properties of sensory cortical circuits.

Adolescent↗

PubMed2005

Relationship between steady-state and induced gamma activity to motion.

When a moving stimulus is presented at a specific temporal frequency, both steady-state responses and induced gamma activity may be elicited in the electroencephalogram. The electroencephalogram was recorded when study participants viewed random dot kinematograms under three conditions: coherent motion, incoherent motion and stationary. Dot position was changed at a rate of 9.3 Hz in the coherent and incoherent conditions. Induced power at 40 Hz was increased during coherent motion compared with the other conditions. In contrast, the steady-state response at 9.3 Hz showed a trend for increased power during the incoherent condition. These results suggest that steady-state responses to moving stimuli reflect sensory activation, while the induced gamma activity indexes perceptual processes.

Adult↗

PubMed2005

Steady state visual evoked potential abnormalities in schizophrenia.

OBJECTIVE: The steady state visual evoked potential (SSVEP) can be used to test the frequency response function of neural circuits. Previous studies have shown reduced SSVEPs to alpha and lower frequencies of stimulation in schizophrenia. We investigated SSVEPs in schizophrenia at frequencies spanning the theta (4Hz) to gamma (40Hz) range. METHODS: The SSVEPs to seven different frequencies of stimulation (4, 8, 17, 20, 23, 30 and 40Hz) were obtained from 18 schizophrenia subjects and 33 healthy control subjects. Power at stimulating frequency (signal power) and power at frequencies above and below the stimulating frequency (noise power) were used to quantify the SSVEP responses. RESULTS: Both groups showed an inverse relationship between power and frequency of stimulation. Schizophrenia subjects showed reduced signal power compared to healthy control subjects at higher frequencies (above 17Hz), but not at 4 and 8Hz at occipital region. Noise power was higher in schizophrenia subjects at frequencies between 4 and 20Hz over occipital region and at 4, 17 and 20Hz over frontal region. CONCLUSIONS: SSVEP signal power at beta and gamma frequencies of stimulation were reduced in schizophrenia. Schizophrenia subjects showed higher levels of EEG noise during photic stimulation at beta and lower frequencies. SIGNIFICANCE: Inability to generate or maintain oscillations in neural networks may contribute to deficits in visual processing in schizophrenia.

Adult↗

PubMed2004

Neural synchronization deficits to auditory stimulation in bipolar disorder.

Patients with bipolar disorder show cognitive deficits and disorganized behavior, which may reflect a disturbance in neural synchronization. We tested whether EEG measures of auditory neural synchronization were abnormal in bipolar disorder. Nineteen symptomatic patients with bipolar disorder and 32 non-psychiatric control subjects were evaluated. Click trains (500 ms duration) presented at 20, 30, 40 and 50 Hz were used to evoke EEG synchronization. Patients with bipolar disorder showed reduced power across the frequencies of stimulation. Phase-locking across trials was also disturbed in bipolar disorder, consistent with poor phase synchronization between the stimulus and EEG. Abnormal high frequency neural synchronization may contribute to cognitive deficits in bipolar disorder.

Acoustic Stimulation↗