Biomedical subjects

Jennifer M Groh

Publications and source records attributed to Jennifer M Groh.

9 recordsLinked to original sources

PubMed2006

Effects of reward and behavioral context on neural activity in the primate inferior colliculus.

Neural activity in the inferior colliculus (IC) likely plays an integral role in the processing of various auditory parameters, such as sound location and frequency. However, little is known about the extent to which IC neural activity may be influenced by the context in which sounds are presented. In this study, we examined neural activity of IC neurons in the rhesus monkey during an auditory task in which a sound served as a localization target for a saccade. Correct performance was rewarded, and the magnitude of the reward was varied in some experiments. Neural activity was also assessed during a task in which the monkey maintained fixation of a light while ignoring the sound, as well as when sounds were presented in the absence of any task. We report that neural activity increased late in the trial in the saccade task in 58% of neurons and that the level of activity throughout the trials could be modulated by reward magnitude for many neurons. The late-trial neural activity similarly increased in the fixation task in 39% of the neurons tested for this task but was not observed when sounds were presented in the absence of a behavioral task and reward. Together, these results suggest that a reward-related signal influences neural activity in the IC.

Acoustic Stimulation↗

PubMed2006

Seeing sounds: visual and auditory interactions in the brain.

Objects and events can often be detected by more than one sensory system. Interactions between sensory systems can offer numerous benefits for the accuracy and completeness of the perception. Recent studies involving visual-auditory interactions have highlighted the perceptual advantages of combining information from these two modalities and have suggested that predominantly unimodal brain regions play a role in multisensory processing.

Animals↗

PubMed2006

The "other" transformation required for visual-auditory integration: representational format.

Multisensory integration of spatial signals requires not only that stimulus locations be encoded in the same spatial reference frame, but also that stimulus locations be encoded in the same representational format. Previous studies have addressed the issue of spatial reference frame, but representational format, particularly for sound location, has been relatively overlooked. We discuss here our recent findings that sound location in the primate inferior colliculus is encoded using a "rate" code, a format that differs from the place code used for representing visual stimulus locations. Possible mechanisms for transforming signals from rate-to-place or place-to-rate coding formats are considered.

Analysis of Variance↗

PubMed2005

Long lasting attenuation by prior sounds in auditory cortex of awake primates.

How the brain responds to sequences of sounds is a question of great relevance to a variety of auditory perceptual phenomena. We investigated how long the responses of neurons in the primary auditory cortex of awake monkeys are influenced by the previous sound. We found that responses to the second sound of a two-sound sequence were generally attenuated compared to the response that sound evoked when it was presented first. The attenuation remained evident at the population level even out to inter-stimulus intervals (ISIs) of 5 s, although it was of modest size for ISIs >2 s. Behavioral context (performance versus non-performance of a visual fixation task during sound presentation) did not influence the results. The long time course of the first sound's influence suggests that, under natural conditions, neural responses in auditory cortex are rarely governed solely by the current sound.

Acoustic Stimulation↗

PubMed2005

Representation of eye position in primate inferior colliculus.

We studied the representation of eye-position information in the primate inferior colliculus (IC). Monkeys fixated visual stimuli at one of eight or nine locations along the horizontal meridian between -24 and 24 degrees while sounds were presented from loudspeakers at locations within that same range. Approximately 40% of our sample of 153 neurons showed statistically significant sensitivity to eye position during either the presentation of an auditory stimulus or in the absence of sound (Bonferroni corrected P < 0.05). The representation for eye position was predominantly monotonic and favored contralateral eye positions. Eye-position sensitivity was more prevalent among neurons without sound-location sensitivity: about half of neurons that were insensitive to sound location were sensitive to eye position, whereas only about one-quarter of sound-location-sensitive neurons were also sensitive to eye position. Our findings suggest that sound location and eye position are encoded using independent but overlapping rate codes at the level of the IC. The use of a common format has computational advantages for integrating these two signals. The differential distribution of eye-position sensitivity and sound-location sensitivity suggests that this process has begun by the level of the IC but is not yet complete at this stage. We discuss how these signals might fit into Groh and Sparks' vector subtraction model for coordinate transformations.

Acoustic Stimulation↗

PubMed2005

Eye-centered, head-centered, and complex coding of visual and auditory targets in the intraparietal sulcus.

The integration of visual and auditory events is thought to require a joint representation of visual and auditory space in a common reference frame. We investigated the coding of visual and auditory space in the lateral and medial intraparietal areas (LIP, MIP) as a candidate for such a representation. We recorded the activity of 275 neurons in LIP and MIP of two monkeys while they performed saccades to a row of visual and auditory targets from three different eye positions. We found 45% of these neurons to be modulated by the locations of visual targets, 19% by auditory targets, and 9% by both visual and auditory targets. The reference frame for both visual and auditory receptive fields ranged along a continuum between eye- and head-centered reference frames with approximately 10% of auditory and 33% of visual neurons having receptive fields that were more consistent with an eye- than a head-centered frame of reference and 23 and 18% having receptive fields that were more consistent with a head- than an eye-centered frame of reference, leaving a large fraction of both visual and auditory response patterns inconsistent with both head- and eye-centered reference frames. The results were similar to the reference frame we have previously found for auditory stimuli in the inferior colliculus and core auditory cortex. The correspondence between the visual and auditory receptive fields of individual neurons was weak. Nevertheless, the visual and auditory responses were sufficiently well correlated that a simple one-layer network constructed to calculate target location from the activity of the neurons in our sample performed successfully for auditory targets even though the weights were fit based only on the visual responses. We interpret these results as suggesting that although the representations of space in areas LIP and MIP are not easily described within the conventional conceptual framework of reference frames, they nevertheless process visual and auditory spatial information in a similar fashion.

Acoustic Stimulation↗

PubMed2004

Auditory saccades from different eye positions in the monkey: implications for coordinate transformations.

Auditory spatial information arises in a head-centered coordinate frame, whereas the saccade command signals generated by the superior colliculus (SC) are thought to specify target locations in an eye-centered frame. However, auditory activity in the SC appears to be neither head- nor eye-centered but in a reference frame that is intermediate between both of these reference frames. This neurophysiological finding suggests that auditory saccades might not fully compensate for changes in initial eye position. Here, we investigated whether the accuracy of saccades to sounds is affected by initial eye position in rhesus monkeys. We found that, on average, a 12 degrees horizontal shift in initial eye position produced only a 0.6 to 1.6 degrees horizontal shift in the endpoints of auditory saccades made to targets at a range of locations along the horizontal meridian. This shift was similar in size to the modest influence of eye position on visual saccades. This virtually complete compensation for initial eye position implies that auditory activity in the SC is read out in a manner that is appropriate for generating accurate saccades to sounds.

Acoustic Stimulation↗

PubMed2003

A monotonic code for sound azimuth in primate inferior colliculus.

We investigated the format of the code for sound location in the inferior colliculi of three awake monkeys (Macaca mulatta). We found that roughly half of our sample of 99 neurons was sensitive to the free-field locations of broadband noise presented in the frontal hemisphere. Such neurons nearly always responded monotonically as a function of sound azimuth, with stronger responses for more contralateral sound locations. Few, if any, neurons had circumscribed receptive fields. Spatial sensitivity was broad: the proportion of the total sample of neurons responding to a sound at a given location ranged from 30% for ipsilateral locations to 80% for contralateral locations. These findings suggest that sound azimuth is represented via a population rate code of very broadly responsive neurons in primate inferior colliculi. This representation differs in format from the place code used for encoding the locations of visual and tactile stimuli and poses problems for the eventual convergence of auditory and visual or somatosensory signals. Accordingly, models for converting this representation into a place code are discussed.

Acoustic Stimulation↗

PubMed2003

Eye position affects activity in primary auditory cortex of primates.

BACKGROUND: Neurons in primary auditory cortex are known to be sensitive to the locations of sounds in space, but the reference frame for this spatial sensitivity has not been investigated. Conventional wisdom holds that the auditory and visual pathways employ different reference frames, with the auditory pathway using a head-centered reference frame and the visual pathway using an eye-centered reference frame. Reconciling these discrepant reference frames is therefore a critical component of multisensory integration. RESULTS: We tested the reference frame of neurons in the auditory cortex of primates trained to fixate visual stimuli at different orbital positions. We found that eye position altered the activity of about one third of the neurons in this region (35 of 113, or 31%). Eye position affected not only the responses to sounds (26 of 113, or 23%), but also the spontaneous activity (14 of 113, or 12%). Such effects were also evident when monkeys moved their eyes freely in the dark. Eye position and sound location interacted to produce a representation for auditory space that was neither head- nor eye-centered in reference frame. CONCLUSIONS: Taken together with emerging results in both visual and other auditory areas, these findings suggest that neurons whose responses reflect complex interactions between stimulus position and eye position set the stage for the eventual convergence of auditory and visual information.

Acoustic Stimulation↗