Single Neuron Representation of Memory in the Human Brain
Since the description of amnesia following resection of the temporal lobes in patient H.M. in 1953, it has been known that structures such as the hippocampus are intimately involved in human memory of facts and events. Despite decades of research, the exact role of the hippocampus in forming and retrieving memories is still debated. For example, it is unknown whether the hippocampus is integral to the sense of having seen an item before, even if one cannot recall details such as when or where the item was seen.
Here at Barrow, have an extraordinary opportunity to directly record single-unit neural responses from the medial temporal lobe of awake human patients who have electrodes implanted for clinical monitoring before surgery for otherwise intractable epilepsy). By recording single neuron responses during different types of memory creation and retrieval, we are determining how the fundamental computational units of the brain, single neurons, act to record and recall the memories that form part of our conscious experience.
Figure 1: Two neurons firing in the hippocampus of an epilepsy patient
Single Neuron Representation of Emotion in the Human Brain
Another structure within the medial temporal lobe, the amygdala, is critical to our emotional understanding of the world. For example, animals that have had their amygdalae removed lack a normal fear response to other animals and will often approach too closely. We are exploring how the emotional and social aspects of facial expressions are used by the network of neurons within the amygdala by recording the responses of single neurons in the human amygdala as patients view faces with various emotional expressions. For example, we have shown that single neurons in the human amygdala respond to the race of a face, thereby forming part of a network of brain areas used for social decision making.
Figure 2: Microwires and depth electrode used to record single neuron activity
Deep Brain Stimulation and Electrodes
In the late 1990s and early 2000s, high-frequency electrical stimulation of the thalamus and basal ganglia has been used to treat advanced Parkinson's disease. Its mechanism of action, however, remains uncertain. The choice of target location and stimulation parameters are presently determined by empirical algorithms. A better understanding of the biophysical mechanisms of this therapy could help improve existing therapies and speed deployment of this treatment for patients with other brain disorders such as dystonias and obsessive compulsive disorder (OCD). We are using large-scale finite-element models to compute stimulation-induced electric fields within deep brain structures.
By combining these models with clinical observations, we are determining which aspects of electrode placement and stimulation are most critical to obtain beneficial effects, such as tremor suppression, while minimizing unpleasant sensations. Preliminary results suggest that the angle between the stimulating electrode and nearby tracts of neuronal fibers may be an important determinant of these effects.
Other Research Areas
Biophysics of Neuronal Computation
Synchronous Neuronal Firing