LIP has been the area for studying motion direction discrimination as model of decision-making. In this paper, Katz et al show that deactivation of LIP has little effect on that model task. Deactivating an upstream area, MT, where decision signals are weaker, however, caused a big deficit.
Dissociated functional significance of decision-related activity in the primate dorsal stream. Leor N. Katz, Jacob L. Yates, Jonathan W. Pillow & Alexander C. Huk Nature.
Sure, this is a cautionary tale of correlates does not equal causation. But it is important not to over-interpret the results of lesions/deactivations. They identify *bottlenecks* in neural processing, not contributions. Just because there is no effect of deactivation doesn’t mean that a given area doesn’t contribute. MT could be providing the raw materials that a number of downstream areas, including LIP, use for decision-making. This doesn’t mean that LIP doesn’t contribute to decisions, it just means that it is not the only area that contributes.
This is in line with recent work showing that neural processing is more distributed than previously thought. For example, see:
Siegel, M., Buschman, T.J., and Miller, E.K. (2015) Cortical information flow during flexible sensorimotor decisions. Science. 19 June 2015: 1352-1355. View PDF »
An excellent, comprehensive review of the neurobiology of decision-making by David Freedman and John Asaad.
Neuronal Mechanisms of Visual Categorization: An Abstract View on Decision Making
David J. Freedman and John A. Assad, Annual Review of Neuroscience, 2016
Decision-making due to a gradual ramp of neural firing rates? Nope. There are discrete state changes that are more informative that spike counts.
Single-trial spike trains in parietal cortex reveal discrete steps during decision-making
Kenneth W. Latimer, Jacob L. Yates, Miriam L. R. Meister, Alexander C. Huk, and Jonathan W. Pillow
Science 10 July 2015: 349 (6244), 184–187. [DOI:10.1126/science.aaa4056]
Siegel, M., Buschman, T.J., and Miller, E.K. (2015) Cortical information flow during flexible sensorimotor decisions. Science. 19 June 2015: 1352-1355.
During flexible behavior, multiple brain regions encode sensory inputs, the current task, and choices. It remains unclear how these signals evolve. We simultaneously recorded neuronal activity from six cortical regions (MT, V4, IT, LIP, PFC and FEF) of monkeys reporting the color or motion of stimuli. Following a transient bottom-up sweep, there was a top-down flow of sustained task information from frontoparietal to visual cortex. Sensory information flowed from visual to parietal and prefrontal cortex. Choice signals developed simultaneously in frontoparietal regions and travelled to FEF and sensory cortex. This suggests that flexible sensorimotor choices emerge in a frontoparietal network from the integration of opposite flows of sensory and task information.
Ibos and Freedman show that area LIP is more than just space and spatial attention. They trained monkeys to make decisions based on conjunctions of motion and color. LIP neurons integrated color and motion when it was task-relevant.
Genovesio et al trained monkeys to judge whether red square or blue circle were farther from a reference point. Even though information about the previous trial was irrelevant to the current trial, prefrontal cortex neurons conveyed the outcome of the previous trial and other irrelevant information about it. Information about previous outcomes can often be helpful. This study shows that this is automatically tracked by the prefrontal cortex even when it is not helpful.
Eiselt and Nieder trained monkeys to make greater/less than judgments to line lengths and dot numerosities. They compared neural activity in the prefrontal cortex (PFC), anterior cingulate (AC), and premotor cortex (PMC). The greatest proportion of greater/less than rule neurons were found in the PFC. Further, only the PFC had neurons that were “generalists”; they signaled the greater/less than rules for both judgments. Neurons in other areas were specialized for one judgment or the other.
This is consistent with our work showing that a large proportion of PFC neurons are multifunction, mixed selectivity neurons. They may be key in providing the computational power for complex, flexible behavior. For further reading see:
Rigotti, M., Barak, O., Warden, M.R., Wang, X., Daw, N.D., Miller, E.K., & Fusi, S. (2013) “The importance of mixed selectivity in complex cognitive tasks”. Nature, 497, 585-590, doi:10.1038/nature12160. View PDF
Cromer, J.A., Roy, J.E., and Miller, E.K. (2010) Representation of multiple, independent categories in the primate prefrontal cortex. Neuron, 66: 796-807. View PDF »
Miller Lab alumnus Jon Wallis and crew studied two different types of cost-benefit decisions (delay vs effort). They found that different neurons in the dorsolateral prefrontal cortex, orbitofrontal, and anterior cingulate encoded the different types of decisions. Thus, rather than have neurons encode decisions on an abstract level, frontal cortex neurons encode stimuli based on their exact consequences.
Ranulfo Romo and crew show delta band (1-4 Hz) synchrony between frontal and parietal cortex that varies with decisions. When there were no decisions to be made, frontal-parietal delta was reduced.