A basal dendrite is a dendritic process that originates from the basal aspect of a neuron’s soma, in contrast to apical dendrites. This is most commonly associated with Pyramidal neurons, but has also been described in other cell types, such as dentate granule cells and mitral cells. The specific morphology and function of basal dendrites vary based on species, cell type, and position within the brain. However, basal dendrites generally participate in receiving and integrating synaptic input.

Basal dendrites are a feature of pyramidal neurons and emanate from the base of the soma. These neurons typically have many small basal dendrites along with one large apical dendrite. In mammals, the basal dendrites of pyramidal neurons are typically short tufts but can vary in size, shape, and spine density depending on location. In macaques, the basal dendrites of pyramidal neurons are especially large in the prefrontal cortex relative to other regions. It was found that the basal dendrites of layer II/III pyramidal neurons are simpler and have lower spine density in the primary visual cortex than in higher-order visual areas. This same study also found that, in macaques, the basal dendrites of the prefrontal cortex were especially large, complex, and spiny.

Dendrites of pyramidal neurons, both basal and apical, typically receive excitatory glutamatergic signals, whereas the soma receives inhibitory GABAergic signals. Basal dendrites often receive inputs from cell populations that are distinct from those connected to distal apical dendrites. In many pyramidal neurons, basal and proximal apical dendrites receive inputs from local neural circuits, whereas distal apical dendrites receive inputs from more distant cell populations. In many mammalian CA1 pyramidal neurons, basal and proximal apical dendrites will receive input primarily from CA3 pyramidal neurons, whereas the distal apical dendrites will receive input from neurons in the entorhinal cortex and thalamic nucleus reuniens.

Basal dendrites of neocortical pyramidal neurons primarily receive local signals from lower-order cortical areas in bottom-up, feed-forward circuits. In the layer II/III pyramidal cells of the cortex, basal dendrites receive signals from layer IV neurons and local-circuit excitation. NMDA spikes amplify the signals received simultaneously at a basal dendrite and increase the likelihood of an action potential.

The synapses on the proximal basal dendrites of neocortical pyramidal neurons can be potentiated by pairing EPSPs with back-propagating action potentials. Potentiation of synapses on distal basal dendrites can be initiated by a strong synaptic activation, sufficient to trigger an NMDA spike, and can be facilitated by the neuro-modulatory signal BDNF (Brain-derived Neurotrophic Factor).

It is theorized that the organization of inputs across basal, proximal, apical dendrites, and distal apical dendrites may be functionally significant. The arrangement of signals from distant sources on distal apical dendrites and local signals on basal and proximal apical dendrites may contribute to the pyramidal neuron’s coincidence detection. Alternatively, it is postulated that this arrangement is meant to modulate responsiveness to local signals.

Caffeine has been observed to increase the length, number and branching of spines on basal dendrites of CA1 hippocampal neurons. It is believed that these effects are mediated by long-term potentiation in hippocampal synapses.

A recent study posits that physical exercise contributes to the structural plasticity of the hippocampus by increasing spine density of CA1 basal dendrites. It is believed this effect is mediated by IGF-1 upregulation.