Arnold Starr

An Integrated-Circuit Approach to Extracellular Microelectrodes

This paper describes a new multielectrode microprobe which utilizes integrated-circuit fabrication techniques to overcome many of the problems associated with conventional microelectrodes. The probe structure consists of an array of gold electrodes which are supported on a silicon carrier and which project beyond the carrier for a distance of about 50 ? to allow a close approach to active neurons. These electrodes are covered with a thin (0.4-?) layer of silicon dioxide which is selectively removed at the electrode tips using high-resolution photoengraving techniques to define the recording areas precisely. The processing sequence described permits any two-dimensional electrode array to be realized. Interelectrode spacings can be accurately controlled in the range from 10 to 20 ? or larger, and electrode-tip diameters can be as small as 2 ?.

Auditory averaged evoked potentials in man during selective binaural listening

Abstract Average evoked potentials (AEPs) to clicks were obtained while a subject performed a selective listening task: the stimuli consisted of a series of numbers, letters and clicks, with separate series presented to each ear. Subjects were instructed to attend to one or the other ear and at different times to report the letters or clicks. The results show enhancement of a late positive component of the click AEP when clicks, but not when letters were reported. No differences in the AEP were found for those clicks presented in the attended ear as compared to those in the rejected (non-attendant) ear.

Verbal and motor memory in the amnestic syndrome

Abstract the subject of this study was a 43-year old man who developed a disorder of memory following herpes simplex encephalitis six years earlier. Recent memory was severely affected in contrast to the preservation of both intellect and immediate and remote memory. The impairment of recent memory functions was evident on tasks using verbal material whereas memory for motor tasks such as maze learning and the rendering of new compositions for the piano was preserved. The deficit in remembering verbal items varied with (1) the type of retrieval (recall vs. recognition), (2) the modality of stimulus presentation (acoustic vs. visual), and (3) the way in which learning was attempted (serial presentation vs. self-ordering and classification). Evidence of proactive interference in memory formation was demonstrated by intrusion errors.

Auditory specificity in unit recordings from cat's visual cortex.

Abstract A substantial percentage of cells in the primary visual cortex of the cat can be activated by nonvisual stimuli. Twenty-five cells were studied in detail in five cats and their responses to visual and acoustic stimuli tested. While all units could be activated by visual stimuli, seven of these responded to visual and acoustic stimulation. Analysis with frequency-modulated tones showed that these seven units were responsive to specific parameters of the sound stimuli. Twodimensional maps done with a small disc on a contrasting background showed that these units have, in addition, visual receptive fields.

Absence of visually influenced cells in auditory cortex of normal and congenitally deaf cats

Abstract Single cells recorded from primary auditory cortex (AI and AII) of unanesthetized paralyzed cats were tested for responses to visual stimulation. Fortysix cells recorded from normal animals responded to acoustic stimuli but showed no discrete response to light flashes or small spots and bars. Twenty-two cells recorded from a congenitally deaf cat were spontaneously active but showed no discrete response to either auditory or visual stimulation.

The effect of body temperature on the “periodic complexes” of subacute sclerosing leucoencephalitis (SSLE)

Abstract The “periodic complex” associated with subacute sclerosing leucoencephalitis is highly responsive to alterations in body temperature. At an elevation in body temperature, the complexes progressively decrease in frequency and amplitude and are eventually abolished. A lowering of the body temperature has the opposite effect. Studies of the VER and H reflex at varying temperatures suggest that the changes in the periodic complexes are mediated by alterations in synaptic activity.

Distribution of frequency following responses in cat cochlear nucleus to sinusoidal acoustic signals.

Abstract We have investigated the frequency following response (FFR) to pure tones in the cochlear nucleus of anesthetized cats with regard to the spatial distribution of amplitude and phase. Amplitude distributions were variable from animal to animal and showed a range of responses including single and multiple peaks and nulls, broad plateaus, and gradually tapering slopes. In general, amplitudes were larger in the ventral cochlear nucleus and VIIIth nerve than in dorsal cochlear nucleus. Phase distributions displayed gradual phase shifts across the nucleus as well as abrupt phase changes in the order of 0.5 cycle. Stimulus frequency had a greater effect upon the dorso-ventral profile of both phase and amplitude of the FFR than did the horizontal position of the electrode track within the cochlear nucleus. Changing stimulus intensity altered the amplitude profile of the FFR at a given frequency but had relatively little effect upon the phase distribution. Our data are consistent with the following hypotheses: (1) the FFR is generated as an envelope of the VIIIth nerve action potentials as the nerve arborizes and terminates in the cochlear nucleus. Phase shifts may be caused by traveling action potentials along the nerve and/or by volume conduction from different fiber bundles to regions lying between these bundles; (2) the FFR is generated postsynaptically in cochlear nucleus cells innervated by the VIIIth nerve. Once again, phase shifts may reflect the sequential innervation of adjacent dendrites, a ‘traveling’ postsynaptic wave, or the response of a few generators at different loci driven at different phases, in which case spatial phase shifts are caused by the summing of responses as currents are volume conducted to the recording electrode.