Biomedical subjects

M N Franowicz

Publications and source records attributed to M N Franowicz.

3 recordsLinked to original sources

PubMed2001

Coding specificity in cortical microcircuits: a multiple-electrode analysis of primate prefrontal cortex.

Neurons with directional specificities are active in the prefrontal cortex (PFC) during tasks that require spatial working memory. Although the coordination of neuronal activity in PFC is thought to be maintained by a network of recurrent connections, direct physiological evidence regarding such networks is sparse. To gain insight into the functional organization of the working memory system in vivo, we recorded simultaneously from multiple neurons spaced 0.2-1 mm apart in monkeys performing an oculomotor delayed response task. We used cross-correlation analysis and characterized the effective connectivity between neurons in relation to their spatial and temporal response properties. The majority of narrow (<5 msec) cross-correlation peaks indicated common input and were most often observed between pairs of neurons within 0.3 mm of each other. Neurons recorded at these distances represented the full range of spatial locations, suggesting that the entire visual hemifield is represented in modules of corresponding dimensions. Nearby neurons could be activated in any epoch of the behavioral task (stimulus presentation, delay, response). The incidence and strength of cross-correlation, however, was highest among cells sharing similar spatial tuning and similar temporal profiles of activation across task epochs. The dependence of correlated discharge on the functional properties of neurons was observed both when we analyzed firing from the task period as well as from baseline fixation. Our results suggest that the coding specificity of individual neurons extends to the local circuits of which they are part.

Action Potentials↗

PubMed2001

The sensory nature of mnemonic representation in the primate prefrontal cortex.

A long-standing issue concerning the function of the primate dorsolateral prefrontal cortex is whether the activity of prefrontal neurons reflects the perceived sensory attributes of a remembered stimulus, or the decision to execute a motor response. To distinguish between these possibilities, we recorded neuronal activity from monkeys trained to make a saccade toward the brighter of two memoranda, under conditions of varied luminance. Our results indicated that during the delay period when sensory information was no longer available, neuronal discharge was modulated by the luminance of the stimulus appearing in the receptive field, and was directly correlated with psychophysical performance in the task. The findings suggest that although prefrontal cortex codes for a diversity of representations, including the decision for an impending response, a population of neurons maintains the dimensional attributes of remembered stimuli throughout the delay period, which allows for flexibility in the outcome of a mnemonic process.

Action Potentials↗

PubMed1995

Comparison of evoked potentials and high-frequency (gamma-band) oscillating potentials in rat auditory cortex.

1. Transient and steady-state (40 Hz) evoked potentials, as well as spontaneous and click-evoked gamma-band oscillations, were recorded from 15 lightly anesthetized rats using an 8 x 8 electrode epipial array covering auditory cortex and adjacent areas to determine and compare the spatiotemporal distributions of these four phenomena. 2. The transient evoked response replicated earlier findings in our laboratory, consisting of an initial biphasic sharp wave in area 41, a similar but delayed biphasic sharp wave in area 36, and more widely distributed slow-wave components. Spatiotemporal analysis supported a model of parallel and asynchronous activation of distinct groups of thalamocortical projections underlying the neurogenesis of these temporal components of the middle-latency auditory evoked potential (MAEP) complex. 3. The 40-Hz response to click trains was superimposed on a steady potential shift (SP), both of which were localized within primary auditory cortex. Epipial distributions of the SP were similar to those of the shortest-latency negative peak in area 41 recorded in the same animals, suggesting similar neural generators. The 40-Hz response was more focal and dissimilar from the SP and any other temporal components of the MAEP complex, suggesting that a unique subpopulation of cells underlies its neurogenesis. 4. Spontaneous gamma-band activity, as assessed by power spectrum analysis, was localized to primary and secondary auditory cortex but had a variable distribution between rats that did not conform to the cytoarchitectonic boundaries within subdivisions of this region. Digital movies computed for individual bursts of gamma-activity indicated a high degree of spatiotemporal variability within and between bursts. 5. Single-trial spectral analysis of click responses indicated an inhibition of gamma-band oscillations during most of the MAEP complex, with subsequent enhanced gamma-activity during the 300- to 350-ms slow-wave component that outlasted the MAEP by approximately 500 ms. The epipial distributions of prestimulus and enhanced poststimulus gamma-oscillations were the same. In contrast to the 40-Hz response to click trains, phase-locking of gamma-oscillations by the single click stimulus was not observed. 6. These results suggest that both the MAEP complex and the steady-state 40-Hz response with its associated SP are highly stereotyped in lightly anesthetized rodent cortex. Their spatiotemporal distributions are probably determined in large part by asynchronous activation of parallel thalamocortical projection systems. Our data suggest no direct link between either the MAEP or the steady-state 40-Hz response to spontaneous or evoked gamma-band oscillations in auditory cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗