Sleep spindles are seen in which stage

Sleep spindles are bursts of neural oscillatory activity that are generated by interplay of the thalamic reticular nucleus (TRN) and other thalamic nuclei during stage 2 NREM sleep in a frequency range of ~11 to 16 Hz (usually 12-14 Hz ) with a duration of 0.5 seconds or greater (usually 0.5-1.5 seconds) After generation in the TRN, spindles are sustained and relayed to the coex by a thalamo-thalamic and thalamo-coical feedback loops regulated by both GABAergic and NMDA-receptor mediated glutamatergic neurotransmission. Sleep spindles have been found in all tested mammalian species and in vitro cells. Ref: guyton and hall textbook of medical physiology 12 edition page number: 822,823,824