What fraction of dopaminergic neurons in the mushroom body receive input from all sensory modalities? 

The integration of sensory modalities in the mushroom body (MB) of insects, particularly through dopaminergic neurons (DANs), is a complex process that involves various types of inputs and outputs, reflecting the intricate nature of learning and memory. The mushroom body is a critical brain structure for processing and integrating multimodal sensory information, and its dopaminergic neurons play a crucial role in memory formation and updating the value of sensory cues. Dopaminergic neurons in the Drosophila mushroom body are known to receive inputs from different sensory modalities, including olfactory, visual, and gustatory signals. These inputs are processed and integrated to drive associative learning and memory formation. However, the fraction of DANs that receive input from all sensory modalities is not explicitly detailed in the provided contexts. Instead, the research highlights the diversity and specificity of DAN inputs and their roles in sensory integration and memory processing. For instance, certain DANs are specifically involved in olfactory learning by forming reciprocal synapses with Kenyon cells, indicating a more specialized rather than universally multimodal input system. Similarly, visual and olfactory memories involve overlapping but distinct subsets of DANs and mushroom body intrinsic neurons, suggesting that while there is some level of integration, it is not uniform across all DANs. Moreover, the mushroom body's architecture, with its distinct compartments and the specific connectivity patterns of DANs, supports the functional relevance of DAN sub-classification, where different DAN subtypes are associated with different memory processes rather than a single group of DANs receiving all types of sensory inputs. This is further supported by the finding that DANs in the mushroom body encode the innate value of odors and update the current value by inducing plasticity during olfactory navigation, indicating a role in non-associative learning that is specific to olfactory cues. In summary, while the mushroom body's dopaminergic neurons are crucial for integrating sensory information to regulate learning and memory, the data does not specify a fraction of DANs that receive input from all sensory modalities. Instead, the evidence points towards a more nuanced view where different DANs may specialize in processing different types of sensory information, with some level of integration occurring within the mushroom body's complex circuitry.

The connectome of the adult Drosophila mushroom body provides insights into function

Dopaminergic neurons in the mushroom body receive input from all sensory modalities, showing unexpected structure in sensory inputs and modulation of information transfer.

Dopaminergic neurons dynamically update sensory values during navigation

Not addressed in the paper.

Tyrosine hydroxylase-immunoreactive neurons in the mushroom body of the field cricket, Gryllus bimaculatus

Four distinct classes of dopaminergic neurons in the mushroom body of the field cricket receive input from all sensory modalities, as revealed by tyrosine hydroxylase immunocytochemistry.

Dopamine signals integrate innate and learnt valences to regulate memory dynamics

Not addressed in the paper.