Encoding of Depth in Parietal Reach Region (PRR)
Rajan Bhattacharyya, Richard Andersen

Technological developments in the past decade have accelerated the pace of research in brain computer interfaces. Multiple research groups across the country are pursuing this area of research as a possible solution to spinal cord injury. The Andersen lab at Caltech specializes in studying brain areas in the parietal cortex, which is associated with vision and motor planning, and in particular the Parietal Reach Region (PRR) which encodes the plan for the next intended reach movement, which is markedly different than the approach taken by other research groups which are using the motor cortex as the source of control signal. The Cortical Prosthetic Project at the Andersen lab has multiple research areas, including the development of an implantable chip to read signals from the parietal cortex, development of computational models for the neural signals involved, development of an online decoding algorithm for the intended movements, and finally the implementation of the real time control of a robotic arm through a brain computer interface.

This project seeks to investigate the encoding of depth by PRR neurons by carrying out experiments that in essence characterize the system. The first experiment will involve training non-human primates to maintain fixed eye positions while reaching to targets at various locations in three dimensional space. The second experiment will have the primates vary eye positions, however maintain fixed reach locations. Subsequently, we will investigate the neural mechanism by which PRR neurons encode the intended three dimensional reach location and develop a computational model to simulate the process. Lastly, we will augment the online decoding algorithm that is under development to decode PRR signals from implanted arrays in non human primates to control a robotic arm in real time to make reaches to locations in three dimensional space. (full report)

Reward Expectancy in Dorsomedial Frontal Cortex
of the Macaque Monkey
M. Campos, B. Breznen, and R. A. Andersen

We recorded neural activity from the dorsomedial frontal cortex of two macaque monkeys during the performance of memory guided and object based saccade tasks. Target locations in both tasks were identical, and event defined intervals could be readily compared across tasks. In about 75% of the recorded neurons we observed a burst of activity during the interval following the instructed saccade in both tasks. The majority (65%) of these neurons also showed a shift in the onset time of this burst from one task to the other. The burst occurred immediately after the target-acquiring saccade in the object based task, but with a ~250ms delay in the memory guided task. The timing of the burst corresponded to the appearance of the visual feedback that indicated to the monkey that he successfully completed the task. Furthermore, in successful trials the burst terminated with the delivery of the reward, but in error trials, in which the monkey attempted the proper saccade but was not rewarded, the burst was sustained for up to 2 seconds. We interpret these results to mean that the burst activity in these cells reflects an expectation of a reward, and that it persists until the reward is obtained.

The Involvement of the Anterior Cingulate Cortex in Novelty
Han C.J., Anderson D.J., & Koch, C.

The activation of the anterior cingulate cortex was previously shown to correlate with novelty detection. However, whether the anterior cingulate cortex is necessary to novelty detection is unclear. We set up a novelty object paradigm in mice. Mice were brought to the testing room in their home cage. A group of mice received a novel object (a corning 15 ml tube), a group received the same procedure including lifting the cage lid but not the object, and a group received nothing. We showed that the novel object readily induces the exploratory behaviors of the mouse directed towards the novel object, and cage lid lifting induces general exploratory behaviors. The sum of time that the group receiving the novel object and the group receiving the lid lifting spend in exploratory behaviors are equal, but the exploratory behaviors in the group that received the novel object are mostly directly to the object. c-fos mRNA was used as a surrogate marker to detect neuronal activation by in situ hybridization on brains from each group. Animals from each of the three groups were sacrificed 30 minutes after the first exposure of the stimulus. We discovered that there are more c-fos positive cells in the anterior cingulate cortex of the brain that received the novel object, compared with the other two groups. To answer the question whether the anterior cingulate cortex is necessary for novelty detection, a group of mice received excitotoxic lesions of the anterior cingulate cortex and another group received sham surgery. Behavioral experiments and analyses are being conducted to determine whether the lesions to the anterior cingulate cortex cause any exploratory behavioral changes directed to the novel object.

Decoding Neuroprosthetic Control Signals from Human Parietal Cortex
Daniel Rizzuto, Richard Andersen

Recent work in macaques has shown that different areas of posterior parietal cortex are specialized for planning hand and eye movements (1; 2), and that it is possible to use recordings from these areas to predict the direction of the planned movement (3). Preliminary studies from our group have taken the first step toward identifying the human homologue of the macaque parietal reach region (PRR), which is responsible for planning hand movements (4). However, it is still unknown if neural activity in human PRR exhibits the same spectral characteristics as that in the macaque. To address this question we are working with human participants who have chronically implanted electrodes placed on the surface of cortex and within deep brain regions, often in partial cortex. Recording taken from these participants while they execute delayed reaches allow us to acquire high signal-to-noise intracranial EEG (iEEG) activity from cortical areas during motor planning. Analysis of this neural activity is aimed at determining which properties of the signal can be used to decode and predict planned movement.

Additionally, in order for human PRR to serve as a substrate for neuroprosthetic control signals it must be resistant to pathological reorganization after cortico-spinal tract (CST) injury, an issue which is still a matter of debate. To address this, we have begun using fMRI to examine differences in motor planning activity in quadriplegic patients compared to normal participants. This comparison will allow us to see to what degree the activity in these areas degenerates after CST injury. The results of these studies will provide an assessment of the feasibility of using PRR recordings in patients with CST injury to control a prosthetic device.(full report)