Prospective hippocampus and putamen activations support conditional memory-guided behavior

Memory of past events, in addition to contextual cues, influence conditional behavior. The hippocampus (HPC), medial prefrontal cortex (mPFC), and striatum are important contributors to this process. The mechanisms by which these regions facilitate conditional memory-guided behavior remains unclear. We developed a conditional-associative task in which the correct conditional choice was dependent on the preceding stimulus. We examined activations related to successful conditional behavior and the timing of their contributions. Two distinct networks emerged: (1) a prospective system consisting of the HPC, putamen, mPFC, and other cortical regions, which exhibited increased activation preceding successful conditional decisions; and (2) a concurrent system supported by the caudate, dlPFC, and additional cortical structures that engaged during execution of correct conditional choices. Our findings demonstrate two distinct neurobiological circuits through which memory prospectively biases conditional memory-guided decisions, as well as influence the execution of current choices.

Intra- and crossmodal refractory effects in auditory and somatosensory ERPs

Refractory period effects are defined as a temporal decrement in neural response due to a previous activation of the same system. We varied the ISI and modality of a preceding stimulus to investigate overlapping and distinct neural systems processing auditory and tactile stimuli. Auditory stimuli and tactile stimuli were presented in a sequential, random manner with a duration of 50 ms and an ISI of 1000 or 2000 ms. The P1–N1–P2 complex of event-related potentials (ERP) was analyzed separately for auditory and tactile stimuli, as a function of preceding ISI and modality. Main effects of ISI and modality were found within the time-window of the P1 and P2 (auditory) and P1, N1 and P2 (tactile). These results suggest an overlap in underlying neural systems when stimuli from different modalities are being processed.

Inhibition of Return Arises from Inhibition of Response Processes: An Analysis of Oscillatory Beta Activity

In the orienting of attention paradigm, inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. No consensus has yet been reached regarding the stages of information processing underlying the inhibition. We report the results of an electro-encephalogram experiment designed to examine the involvement of response inhibition in IOR. Using a cue-target design and a target-target design, we addressed the role of response inhibition in a location discrimination task. Event-related changes in beta power were measured because oscillatory beta activity has been shown to be related to motor activity. Bilaterally located sources in the primary motor cortex showed event-related beta desynchronization (ERD) both at cue and target presentation and a rebound to event-related beta synchronization (ERS) after movement execution. In both designs, IOR arose from an enhancement of beta synchrony. IOR was related to an increase of beta ERS in the target-target design and to a decrease of beta ERD in the cue-target design. These results suggest an important role of response inhibition in IOR.

Temporal Nonlinearity During Recovery From Sequential Inhibition by Neurons in the Cat Primary Auditory Cortex

Auditory stimuli occur most often in sequences rather than in isolation. It is therefore necessary to understand how responses to sounds occurring in sequences differ from responses to isolated sounds. Cells in primary auditory cortex (AI) respond to a large set of binaural stimuli when presented in isolation. The set of responses to such stimuli presented at one frequency comprises a level response area. A preceding binaural stimulus can reduce the size and magnitude of level response areas of AI cells. The present study focuses on the effects of the time interval between a preceding stimulus and the stimuli of a level response area in pentobarbital-anesthetized cats. After the offset of a preceding stimulus, the ability of AI cells to respond to succeeding stimuli varies dynamically in time. At short interstimulus intervals (ISI), a preceding stimulus can completely inhibit responses to succeeding stimuli. With increasing ISIs, AI cells respond first to binaural stimuli that evoke the largest responses in the control condition, i.e., not preceded by a stimulus. Recovery rate is nonlinear across the level response area; responses to these most-effective stimuli recover to 70% of control on average 187 ms before responses to other stimuli recover to 70% of their control sizes. During the tens to hundreds of milliseconds that a level response area is reduced in size and magnitude, the selectivity of AI cells is increased for stimuli that evoke the largest responses. This increased selectivity results from a temporal nonlinearity in the recovery of the level response area which protects responses to the most effective binaural stimuli. Thus in a sequence of effective stimuli, a given cell will respond selectively to only those stimuli that evoke a strong response when presented alone.